Would starship be impossible if earth gravity was 10% higher? @Eager_Space on Twitter Triabolical_ on Reddit / eagernetwork / eager-space-1038430522...
"A moving and something exploding target". It's this sort of highly informed precise verbage that has made this you tube channel a must watch for space fans everywhere.
"Verbiage" is generally considered to be a derogatory term ("excessively lengthy or technical speech or writing") but I get your point and agree! This info was useful with some humor. 👍
@@tonybrock5288 Merriam-Webster: “Verbiage has a second sense meaning, simply, "wording," with no suggestion of excess. This second definition has sometimes been treated as an error by people who insist that verbiage must always imply excessiveness, but that sense is well-established and can be considered standard.”
I feel like it's worth noting that increasing gravity would have other very substantial effects too. first, it'd pull the atmosphere down more making pressure higher. it'd have also probably attracted more gas when the planet was was born, so thicker too. additionally, it'd require more thrust to even get off the pad, let alone efficiently, making rockets bigger and more drag-y. But in addition to that, the first stage would need notably more propellant to land, and not only would this be true for repulsively landing stage 2, you'd also be coming in faster, and coming in faster into a likely thicker atmosphere, making the heat shield way more difficult. so honestly. it's likely the case for starship is even worse than you think in higher gravity.
Well, since the original comment talks about air density too I think it is fair to accept that the comment is 'for a given atmospheric density, 10% more gravity would be a problem'. So no - no one said that 'a planet that formed with 10% higher gravity......'
Huh... How about DeltaV? Wouldn't higher gravity planet with same diameter require higher velocities to stay in orbit? TWR, maxQ is one thing, but I think DeltaV would be really hard. Look at difference in DeltaV requirements between Leo, MEO and GEO. F9 can lift 20+ tones to Leo, but 8.5 tones to gto. So if you would need as much deltaV to heavier Leo as currently to gto, probably you wouldn't have any margin for recovery.
@@just_archan ultimately needing a higher twr at lift off means you get less fuel to build horizontal velocity. so yes, you need more delta v to start with, but twr further compounds that issue.
RUclips is not the place to learn rocket science this video is radically oversimplified but it’s correct starship is a serious payload problem. If you really wanna learn this and the complexities of what it really takes with different types of vehicles, get a copy of explain and some textbooks on aeronautical engineering, and Space exploration
Wouldn't higher gravity tend to disproportionately increase gravity losses? Saturn V, for example, only had 1.15 twr, which would drop to 1.05 with 10% more gravity. Which means off the pad 67% less work being done.
This is roughly speaking intentional, since engines are expensive and gravity losses aren't large enough that you should overprovision them, whereas fuel is comparatively cheap despite diminishing returns. A Saturn V densely packed with Raptors could have an incredible T/W.
Yes. But the factor I used applies across across the full cost of getting to orbit, which includes drag and gravity losses. So it's not really true that I'm ignoring them, I'm just assuming they scale at the same rate as the velocity energy does. Which is, as I noted, obviously the wrong thing to do.
More than fair. My instinct is that the "real" answer is probably even more exaggerated than this good approximation suggests, rather than less exaggerated. I think gravity losses would not scale linearly could contribute, but I haven't done that math either.😅
@@darylbardo Gravity losses aren't too large with Starship. It has a T/W of around 1.5 at liftoff, so even with 1.1 times the gravity, the T/W would still be pretty good at something like 1.35. You could also expect that a Starship designed for higher gravity would have had more engines and higher thrust. A Saturn 5 designed for 1.1 times the gravity might have had six F-1 engines. The penalty would primarily have come in the form of added dry mass, cost and complexity, while the reduction in payload would have been modest. The gravity losses may even have been reduced overall, by adding the sixth engine.
Astronauts have a maximum acceleration, gravity is part of that accelertion, so T/W ratio couldn't be increased to compensate for increased gravity. There is also a matter of max Q which limits the early T/W ratio even of unmanned launches. With increased gravity you would also get a denser atmosphere further effecting max Q.
I think you can figure out that I mess up the lines sometimes, that I sometimes rewrite lines on the fly, and that I have a dog who sometimes walks into and out of the room. I don't think I swore in this one, but sometimes that happens when I mess up a line for the fourth time in a row.
@@EagerSpace when you first posted the video I was writing out a comment but couldn't post it because you took the video down. Jokingly I suggested an alternate title; "How the Sausage is Made - Is Elon Right?"
The other possibility is that he's also talking about economically impossible. Robert Foward proposed all sorts of ways for an intelligent inhabitant of a neutron star to get into orbit, which is obviously much more extreme. So there's ways of doing reusability, even from a much more than 10% higher gravity, but they're impossible if it were to require the entire industrial output of the planet to achieve them.
@@saumyacow4435 I'm sure it is. We've had spaceflight for nearly 70 years. The first commercial passenger flight was only 7 years after the first powered flight. It's obviously very hard to do this economically.
no, Elon quite literally meant impossible, the assumptions in this video are wrong, you can't assume a linear increase in parameters when your distance is squared.... delta V behaves like an exponential curve, same with gravity drag, with that alone you get a required fuel mass to get payload to orbit of over 99% of the weight of the whole rocket system getting anything to orbit with rockets becomes impossible
1:30 Misconception here. When you add up E_a and E_v, your resulting energy is going to be the same, whether you burn up before burning sideways, or do an optimized gravity turn. What changes is the gravity losses, which a gravity turn minimizes. Your equations don't "assume" that you go up and then sideways. It works for both scenarios. That detail is hidden in the γ in gravity loss. γ (pitch) varies over time and depends on the specific trajectory that you take. A gravity turn minimizes sin(γ) as early as possible, which happens when the craft turns sideways. So more energy will be put directly into E_v initially, but gravity will exchange that for an equivalent amount of E_a as the altitude increases. In the end, for the same destination orbit, you will get the same values for those two energies no matter what ascent trajectory you use. So it's entirely correct to add up those two values; there is no assumption about the trajectory baked into them.
Yes, I made a *hell* of a simplifying assumption, but I think the answer is at least directionally correct. Building the right simulation for a specific rocket without knowing the real numbers nor knowing the actual flight path they plan to follow doesn't seem very tractable.
Wouldn't more gravity also constitute a thicker atmosphere thus changing how they would have to deal with Max Q throttling or the early stages of flight in general? Also, with that in mind would the overall air frame of the vehicle have to be more robust, leading to a heavier rocket?
Definitely. It would have a much higher altitude to its "edge". it would be more dense where it matters most, plus our entire current atmosphere after that. there may be some aspect of lift from the extra density that would compensate in some way. I'm also not quite sure what percentage it would add to atmospheric density relative to 10% more gravity.
The difference in more gravity & how different the physical characteristics of the vehicle would have to be, is kind of a mute point, because it likely would mean that we would either be somewhat different developmentally/evolutionarily or life might not of even emerged.
@@matthewkantar5583 Those all have vastly different circumstances. A better comparison would be: Titan: M = 135 Et, P = 147 kPa Triton: M = 21 Et, P = 1.5 Pa Pluto: M = 13 Et, P = 1 Pa Similar densities, internal structures, temperatures, and atmospheric compositions.
Yeah I would imagine an increase in gravity as massive as 10% would have second order effects on the circumference of the planet, the rotational speed, the volume and density of the atmosphere, etc... If I had to guess, in that case 400km would literally be impossible for LEO in a planet like that and could be more like anywhere between 450-500km on the low end. Then you would have third order effects on the heat shield on the way back that would need to be much heavier because of the increased LEO speeds and the greater gravity increasing acceleration, which itself makes the ship heavier and necessitate more hardware to cope with it, making it have an exponentially greater cost on the design. You keep stacking design, gravity, drag, reentry, recovery, etc on top of each other and you can see how bad it can get. At the same time if you imagine something like 80% gravity, instead of starship we would probably already have a 1 kiloton to LEO fully reusable rocket that is flown every couple of minutes out of pada around the world like a plane does today.
With higher gravity the atmosphere would probably be thicker and I would guess the extent would be different too… that could matter for reentry… maybe?
@@EagerSpacewell maybe not for launch but reentry i see two key differences Im guessing smaller flaps would be needed But you would need more robust tjermal protection im thinkin tps would cost more in terms of weight then the flaps would save but have no way of checking how big of a penalty that would be
@@yakirfrankoveig8094You could just reenter at a higher altitude with the same air density. The 10% faster orbital velocity would be an issue since it would increase temperature by ~21%.
@@kolbyking2315 yeah i considered reentering higher when i wrote that comment because you enter at the same air density but at a faster speed so you would experience more heat from the begining as you said and it would also persist throught the whole regime since you will also be slowing down quicker and therfore dropping faster into thicker atmosphere than you would on earth
I told my son. "Avoid youtube. " so he found your Chanel and I have to concede. It's very informative and well thought out. But you don't need me to say that. Great content.
It would be interesting to see other rockets' Payload Effect of Different Gravity charts. This also makes me curious about the comparative difficulties of Lunar vs Martian launch vehicles.
My guess is that the expendables are going to have roughly the same shape as Falcon 9 does; definitely true for Vulcan. I think a "payload versus delta v" chart is a bit more interesting and relatable. Lunar and martian both require a lot of delta v and it's not that far apart, so you need the same sort of vehicle for both.
@@EagerSpace So is the moon. Apparently you could manufacture Aluminium structures like girders and plates and throw them into LMO from surface, to build space stations and large spacecraft. No need for on board propellant. The moon could be quite a good ship building yard! What do you think?
Ignoring drag ratios for simplicity was necessary, but it's likely most of where the rest of the "10% is impossible" idea comes from. Of course, Elon is very much one for hyperbole, but still fun to think about. If the earth's gravity were 10% higher, it would stand to reason that the atmosphere would be shorter, and thicker at the bottom. that means that not only is the thrust to weight ratio going to go down from, for example, 1.5 to about 1.35, there would also be greater drag losses in that early stage of flight. wasting 2/3 of your fuel fighting gravity vs wasting 3/4 sort of thing. the booster's delta V would be impacted quite a bit, and if it were aiming for a boostback it'd need to keep more propellant for it's landing and hover. that could take the payload down another 2% easily, and like you said, starship's only hauling 4% as it was and lost the first 2% to the increased orbital velocity. Nice video, hopefully it makes it easier for people to see that elon isn't just waffling lol
That was about average for my raw takes; it was a retake this morning when I finally figured out that the last one had a disk error in the middle and was unusable.
Ignoring drag is where you are going wrong because the acceleration can't be linear due to forces on the rocket at lower altitudes, remember they need to throttle down to go through max Q to make sure the forces at max Q aren't too high, that is how significant the drag forces are. This is most significant at the worst part of the trajectory when the rocket is still really heavy with fuel. Also as gravity increases so does atmospheric density so at higher gravity the effect is even worse. Also higher gravity means you need to go higher to get above the atmosphere in order to achieve a stable orbit that doesn't decay too fast. There are many factors you ignore which validates Musks comment to a far greater extent, though even your univariate analysis shows it right on the edge of feasibility.
A higher gravity doesn't increase the amount of atmosphere. It just increases the density at sea level, while the density drops off faster for higher altitude. The rocket still has to get through the same amount of atmosphere, it just gets through more of it at the start, while it is is moving slow. I think the situation with drag would be improved, overall, if the vehicle is designed for the same TWR. You would clear the densest part of the atmosphere quicker, and you could perform a more aggressive gravity turn.
Also we dont take into account other factors that come from that like sea level thrust in a higher density atmosphere or higher drag to to the hypersonic speeds(speed of sound is lower). So everything points to how much harder this would be.
Drag loss is low, typical around 100 meters per second, or only about 1% of the total energy cost to get to orbit. Rockets just aren't moving very fast down low and they get above the atmosphere fairly quickly. See web.stanford.edu/~cantwell/AA284A_Course_Material/Karabeyoglu%20AA%20284A%20Lectures/AA284a_Lecture7.pdf
@@EagerSpace But what I am saying is that forces due to drag mean that the rocket has to be throttled back in the lower atmosphere operating at below peak efficiency. As with all these things, one small effect impacts many others which in total equal a much larger total impact.
I'd add/nitpick only 2 things: 1: as the rocket equation gives out m/s as a unit and specific energy is m²/s², you'd have to take the square root of your energy multiplier (assuming the value is accurate); and 2: It'd probably be more accurate to say "a x% reduction of the stage's mass at the end of the burn" instead of total mass. So, because falcon's payload represent more of the stage's final mass, you could cut a third of it off and still have half of the payload mass, while starship would lose all of it. Overall, the effect would be very similar, but I think the intensity would be significantly reduced.
It's not just the mass of the thermal protection that directly subtracts from payload mass. Its also the mass you have to add to the second stage such that it will survive the structural loading of re-entry and landing. Rocket Labs did their sums and concluded that a non reusable second stage for Neutron makes economic sense because all they are throwing away is one very light tank (about the mass of a large motorcycle) and one engine. Starship is struggling because it keeps having mass added. Now Elon is talking about more robust (heavier) tiles and an underlayer of ablative material. This was a vehicle originally touted as having a payload to LEO of 150 tonnes.
There's another video in the works that will dig into this a bit more. I haven't done any numbers but I suspect the loading on ascent when it's full of fuel is much higher than re-entry when it's empty. It is in another direction. I am interested in how neutron turns out because it's the optimized partially reusable rocket they SpaceX didn't try to build, and I expect the economics to be good. Starship is ridiculously hard to develop, but Elon's goal isn't lift to Leo, it's Mars.
@@EagerSpace Fuel and tank pressure on ascent will load the walls of the vehicle uniformly and in tension. In descent you've got several things happening that aren't in your favour. Firstly, the dynamic pressure is high - it's equivalent to hurricane force winds. So you end up with higher g forces overall. Secondly, the flaps act on their hinges and the forces from the flaps are then transmitted into the whole structure which is now being torqued - basically it's like pipe bending. You get a bunch of internal elements that want to buckle as a result. Thirdly, on launch you get internal pressure that actually stiffens the structure, but on descent you've got empty tanks and lower pressure. And fourth, you saw the flapping of the steel sheets on the upper sides of the flaps? That's aerodynamics kicking in. It's basically a cylinder doing a belly flop. there's going to be places where the stream separates and turbulence kicks in. So the steel walls will react by flexing or going into vibrational modes. That in turn will react with the dynamics of the gas stream, possibly creating feedbacks. Bottom line here is that there's a lot of movement going on that is trying to shear and separate the tiles. Tiles can work if you've got an absolutely foolproof way of ensuring they don't crack and don't tear out of their mounting points. I think what Elon is now doing is going for denser (thus stronger) tiles, but there's an obvious price to pay for that. I also have doubts about the ablative underlayer, if its silicon based. It's not that that stuff can't survive high temperatures. Rather its the combination of temperature, charring and then high dynamic pressures and turbulence. See Orion's heat shield. One of the nasty things about plasma is that if its focused by geometry and then comes back to touch something, it's very destructive - a cutting torch. To be honest I was feeling better about this when SpaceX announced it's original intention to have transpirational cooling. Yes, it would be experimental but they could have advanced the state of the art quickly. Maybe arrived at some kind of hybrid with a slowly ablative (reusable 10x) material in certain places. And if you want to know what I'm thinking. I'm thinking what happens when we get a stretched version of Neutron and Rocket Labs starts thinking seriously about a reusable second stage, Stuff like a combination of methane cooling for the engine and ballutes for drag, maybe?
That would be funny. It would be a pain to gather the data, however. The interesting thing on Elon Time is that if it's less than 2 months, it's pretty much 1:1. At least in some cases.
"we add these up and we get a very precise answer that's wrong..." 😂 Great videos. I love your calculation based approach and the types of questions you dig into. Thanks a lot! I hope that your channel gets the amount of viewers it deserves.
Also 10% higher gravity well probably requires more structural strength, so the empty mass goes up a little more for both super-heavy and starship. Cuts into both payloads even more.
MECO at 5600 km/h on Starship vs 8000 km/h on Falcon 9 means Starship have 1/2 kinetic energy thus more fuel is needed to reach orbital velocity. Starship should try to land on the Drone ship too.
Yes, but staging earlier reduces the cost of the boostback burn and means that super heavy can give more Delta v to starship. The tradeoff is complex. And yes, a drone ship would make this a lot easier, but it gets in the way of the operational goals.
For some reason I kept this video open in a tab with the intention to write that you and Suchomimus are closely competing for the "best jokes casually being dropped in videos" award in my mind
Remember when the US had a (almost) fully reusable and pretty reliable rocket (and yes, I‘m talking about the Space Shuttle). Didn’t make going to space much cheaper back then.
Intuitively speaking, the sight of the falcon 9 graphs appearing to asymptote to 0 payload capacity makes me think there's some very important factor that's being completely missed, as the extension of the logic of the graph is that Falcon 9 could deliver some marginal payload to orbit... from the event horizon of a black hole.
Saying it's "impossible" may be a bit hyperbolic, but practically speaking, 25t to orbit for a rocket larger and more powerful than Saturn V is... pretty horrible. Barely more than an expendable Falcon 9, so while you could do it, how reasonable would it be to pursue? I could see how full reuse anyway might still be desired to lower costs and increase cadence, but it would be difficult up front, and take longer, to send heavier spacecraft in orbit that way.
yes. But even a big ass scale of production of saturn v's would be more expensive than getting full reusability. Because reusability will give you a monopoly that outweighs every throwaway system. The upfornt cost for digital computers and data handling was absolutely astronomical, until it replaced it by orders of magnitude. I am not an Elon fan either, but this nut needs to be cracked someday. And I don't even think it's going to be Starship, cause the larger you go, the actual better reuse performance you get out of your rocket. The refueling situation will likely be Starships actual killer. Even if Startship is working perfectly, needing a shit ton of refueling missions to perform the actual mission isn't really practical and economical.
And 25t is with my model, which ignores a lot of factors that probably make it lower. There's a biggest discussion to be had, but that will have to wait for the next video...
@Skukkix23 Oh, definitely. Reusability would still be better in the long run, but how would pursuing it be different if it was already difficult to send large payloads to orbit by expending the vehicle? Requiring megarockets to put comparatively meager payloads to orbit may make reusability seem not worth it for a longer time. Astra's idea of 'mass producing' expendable rockets might be pursued instead for a while, attempting to lower costs and increase cadence that way until they hit a ceiling.
@@davidk1308 Yes, I am very much of the opinion of "right tool for the task". And really a lot of stuff would not even require a falcon 9. Just a really cheap rocket would do the trick also. But I am not even remotely qualified to talk about numbers or economics here, also I wouldn't want to come across this. As @EagerSpace mentioned, even 25t is probably generous. I just think full reusability will be a bigger step than actually like discovering a new continent. When you suddenly knew, that there was a new continnent, basically everybody already had ships and the means to travel there. The nation or corporation to get the leap on reusability, will have an exclusive wormhole to multiple new continents. This is highly underrated everywhere you look. Because that continent is maybe not even a different landmass, it's actual economical maneuverability in space. The only reason why we're not more in space is now just a scalable function of cost, not a function of engineering.
@@Skukkix23 Having reusable second stage doesn't make sense ( as you said ) unless it's absurdly big to make use of economy of scale ( which Starship might qualify as ) and only haul stuff to LEO and then come back. When trying to go beyond LEO as is the case with Artemis it's incredibly inefficient which was also the case with Space Shuttle.
This analysis is completely wrong and missed multiple extremely important factors. Besides the increased energy to get into orbit, the rocket itself weights 1.1 times as much. A fully loaded Falcon 9 would weigh 1.1x its current weight, which is about as much of its current payload capacity. The thrust to weight ratio would also be far worse as the engines would get no more powerful, meaning that it spends more time fighting gravity rather than converting its propellant into orbital motion, further decreasing efficiency. Combine that with the increased velocity necessary for orbit, and the payload to orbit of a Falcon 9 on a world with 1.1G would be negative (even just considering the increased wet mass). It couldn’t get anything to orbit, let alone a slight decrease in its current capacity like this video claims. It would essentially be like strapping a 15 ton block of lead to the top of the Falcon 9, while also expecting it to have increased final velocity. (The Falcon 9’s dry mass is way more than 4t btw.)
This. With those calculations F9 could make it to LEO with 2x gravity lol. People don't appreciate how on the edge everything is for a rocket, for that to be even a comparison you need 10% more thrust, 15-20% stronger airframe, and proboly 30-50% extra full (as a guess its probly even worse). So F9 couldn't make it to orbit with no payload.
@@R0nBurgundy It’s a good reminder that just because a video has a lot of views, and a lot of people agreeing with it, it doesn’t mean it’s remotely right.
I get the feeling from these numbers that we're forgetting that orbital velocities, atmospheric depth and density, and actual effective low planetary orbital altitude all will differ with changing gravity. I'm pretty sure that is the context in which Elon is making his assertion.
TWR with 10% more gravity is: Nominal F9 - Launch- 1.28TWR, 10% more gravity 1.15TWR, this results in more time ascending, more time in atmosphere, more drag, overall slower acceleration = failure to reach orbit. Tried this in KSP-RSS with F9 and it's borderline impossible. Your data needs to be revised. Purely on DV is possible, but the time thrusting is too long. Subscribed!
If gravity was 10% higher, the Falcon 9 might have been a Falcon 10. Or more likely, it wouldn't have been stretched as much. Keeping TWR at an acceptable level but also reducing the payload capacity.
@@SpaceAdvocate Yeah, true, but you'll have put additional fuel if you need to burn for the same duration. Rocket equation is a b***h. Guess it's good think that our gravity is 9,8 not 10.78 m/s/s. Off to try Falcon 10 :)
It might have been interesting to put in the space shuttle for comparison too. I would imagine it fares similarly poorly to Starship. There is one extra consideration as well that you omitted: On an Earth+10% gravity planet, even the reduced payload rockets couldn't fly. They have the deltaV potential. But they don't have the thrust to accelerate as fast against the increased gravity, so gravity losses would increase a lot. To resolve it, you would need to increase engine thrust by 10% too. For example adding an 10th engine to the Falcon 9 (and renaming it to Falcon 10), which comes with the empty weight penalty of 1 more engine, further reducing your payload. So in reality it's probably worse than your numbers might suggest.
It really depends on what you mean by "10% higher gravity" and what factors you include in that. If we reduce Earth's radius to 6074 km, that should do the trick, but adds less than 200 m/s dv to orbital velocity while compressing the height of the atmosphere, allowing you to perform more aggressive gravity turns and reach the top of the atmosphere equally easily to on Earth. On the flip side, if you add 26% to Earth's mass while composition is held constant, you end up with ~675 extra DV required. If you inflate the Earth while holding density constant (reducing compositional density by 3.2% in the process), you get a nasty 790 m/s increase. However, it should be mentioned that habitable planets, super Earth's, not mini-neptunes with thick helium envelopes, can definitely go beyond 10% higher gravity. A 2 Earth mass planet with a composition 20% denser uncompressed than Earth would have slightly over 1.5 G and an orbital velocity of 10 km/s. Worse still, just because it doesn't have 1000 bar of helium or something doesn't mean it has none, and even a bit of helium is gonna be enough to make that atmosphere very, very tall, forcing rockets to climb way way way up to get out of it.
I am ironically of the opinion that a higher gravity environment might be beneficial for space travel, even if it spells hell for reusable chemical rockets. The reason is Project Orion. If you live on a planet where chemical rockets are literally infeasible, then there is a greater impetus given the same level of drive for space exploration to consider the literal nuclear option. Add in the fact that Orion sneezes at 1 km/s increments in delta-v anyway, and that once you do make it to orbit you now have ion-drive level efficiencies combined with chemical-level thrusts, I honestly think the net result this would have an on a super-Earth's space program would be largely beneficial.
I'd be skeptical that any entity would be willing to cough up the funding for such a project without the proven history of small launch vehicles. Maybe there is a balance point in there somewhere though.
If you look at the energy requirements from first principles, i would have structured the terms as: 1) Energy that goes into the (dry mass) of the rocket (kinetic energy and gravitational potential of payload and all spent stages) 2) Energy that goes into the atmosphere through friction And 3) energy that goes into the rocket exhaust. Functionally, gravity losses are part of 3), you are heating up and accelerating propellant without really adding velocity to your spacecraft. But even in a perfectly empty universe with no gravity, part of the energy used would be in the exhaust cloud, so 3) is more than just gravity losses.
@EagerSpace Maybe, but this sort of analysis would (in my opinion) probably be way to much work to expect from a RUclips video. And, ultimately, the total energy requirements, and where that energy ends up, aren't even THAT interesting. What we really care about is the payload capacity. I think your approach where you look at effective Δv requirements, and assume they scale linearly with the orbit velocity of LEO (sqrt of g) is a very natural first estimate, especially for relatively small pertubations of g+-10%.
Great video, and yes attaining orbital velocity is the biggest fuel requirement, but gravity drag or losses are partly a a factor of time to orbit, the greater the time the greater the drag, hence as weight is greater, hence the acceleration is lower as the thrust to weight ratio is lower over much of the flight which leads to a significant increase in time as lower acceleration figures means longer to get to orbital velocity, added to this the orbital velocity required is higher than earth due to greater gravitational field strength, hence a multiplying of 2 factors. And as you so clearly pointed out any increase the needed fuel mass equates to a reduction in payload, hence according to some models the mass to orbit is even worse. But once again, thanks for all the excellent videos and in depth research and presentations.
Thanks. I've talked about gravity losses before - there's a video on them - but it's not very easy to explain or understand, because - as you note - it depends on time to orbit and it also depends on flight path.
The 1st thing is that with a single pad, a fully reusable rocket can only have (1 or) 2 stages, the 1st one returns to launch pad, and the second one has to do a full orbit. This video observes the effect to a 2-stage rocket. If you had a ring of pads aligned around the Earth, then you could have any number of stages technically,. The interesting case is 3 stages, but then when you land the 2nd (out of 3) stage at the next pad, you can't launch again if you don't have a next-next pad (due to earth rotation you only want to launch East-ward). So you want a full ring around in the only inclination that you want to service. Supporting 1 inclination may make sense for Starlink only but even then, you don't have the flexibility to change you mind, this would be hugely impractical if not politically impossible. Okay, Elon quote confirmed xD
This will be in my upcoming answers video because lots of people have asked. The two big issues with more stages are: 1) Inclination. You want to launch everything from due east to different polar orbit (though polar might be a different launch site), and so you need a target that you can get to with your middle stage. It will also have different trajectories depending on what kind of launch you are doing (heavy into LEO, light and hot into something higher (assuming you can do that)). You can't get places that work for everything, which means you likely need crossrange capability, which you really don't want to pay for. 2) Super heavy gets by without a reentry burn by being low and slow. Now you have a stage that's coming back faster, so you have a more fuel intensive reentry path. 3) How do you get the second stage back home?
Why is dV just multiplied by energy ratio as if it was a linear function of energy ratio to get to orbit. It seems counter-intuitive to me because the velocity in the energy expression is second-degree
One can try designing a 3-stage system for higher gravity, while keeping the materials the same. Second staging around 3-4km/s should be good enough and you can still land on the droneship. This reduces fuel and thrust requirements for starship by about 40%.
How do you get the second stage back? It doesn't have enough velocity to go into orbit so you can't control when it reenters and it may need a heart shield or at least a re-entry burn.
@@EagerSpace similar to falcon heavy center stage - drone ship landing. In this case the second stage will be somewhat heavier than first stage of falcon 9, but starship itself will be somewhat smaller, with, say 4 vacuum raptors.
It would be way farther downrange than the Falcon 9 boosters. A couple thousand kilometers minimum, and maybe far enough that you run into europe or africa.
Another great video. Could you do one about the real performance of Starship? Supposedly current version can launch up to 50 t to orbit, while the next one can do more than 100 t. Two question arise here. How can the first value be so low and what can they do to increase it more than two fold?
The current prototypes seem to be capable of carrying around 40-50 tons to LEO. That's pretty good for a fully reuseable vehicle. The previous record was zero. Of course, it's less than what SpaceX is aiming for. But they'll keep working on it.
It'd be very interesting if you could do a breakdown of the kind of rocket/engines required to build a self-sustaining city on Mars (loosely defined as having 1 million people on Mars). If I remember correctly Elon has said that they won't use Raptor for Mars missions, which makes me wonder if they will look into alternate propulsion methods
They will use Raptor and Starship for Mars. Musk has said that long term there will probably be a different engine, but it could just as easily be "Raptor 6.0 Ludicrous Max" or whatever. The current Raptor engines seem to be good enough to colonize Mars, assuming reliability/reuse is improved over the next few years/decades, and get to an extremely high level. They are already very good engines in terms of thrust-to-weight, efficiency, etc.
I don't think there are any practical alternate propulsion methods. There are a lot of nuclear thermal propulsion advocates but they've been saying the same thing for the last 50 years and we have yet to see a real stage. Maybe the current DARPA program will yield one, but I'm not holding my breath on performance. You might get somewhere with a cycler architecture, at least for carrying lots of stuff, but you still need to get it down to the surface at the other end.
Great deductions, but I didn't see taking into account the atmosphere density with gravity difference. Even now Starship barely survives re-entry. Increasing gravity by 10% should definitely have an impact on atmosphere density too. Reusability might be a b1tch if that is taken into account too.
Terrific video! Nice of you to say that Starship can deliver 50 tons to orbit when, in truth, it doesn't seem to be able to get to orbit (yet) with zero payload.
Both the third and fourth flight got to slightly below orbit with several tens of tons of propellant left over. You'd need to burn around 5 tons of propellant to enter orbit, and the remainder of the propellant could basically be replaced with payload. The 40-50 tons figure from Musk seems reasonable going by what we can see on telemetry.
The current set of flights were reportedly only partially fueled so that they got the trajectory they wanted. But yes, they clearly aren't where they want to be yet.
i think this is fine as long as the TWR is still bigger than 1 of the pad, which i think Elon was referring to when he said impossible with 10% more gravity. Really good video nevertheless.
Hi, I don't know if You still answer comment questions in your videos, but there are two that are bugging me for some time now (because I can't definitely answer them). When it comes to cost reductions, is a second stage reuse way less useful than space cadets think? And why isn't Fairing-reuse more often considered (for new rockets and as an upgrade for existing rockets)? Here is my very simplified reasoning. When reuse for the F9 was available for the first time, the F9 costs were 62.7 Mill. $. For a reusable F9 SpaceX talked about 50 Mill., while they kept around half of the savings for themselves. So, around 25 Mill. in savings, and a theoretical price of ~37.5 Mil. Now the upper stage without the fairing. That way it is a smaller version of the first stage. Instead of 9 times cheaper, let's say it is 7 times cheaper than the first stage (more expensive nozzle...). Let's also be absurdly generous and say, that an upper stage without a fairing could be refurbished and reused as easily as the first stage. Even with that, it would only bring an unsatisfying cost reduction of ~3.6 Mill. And in reality, it would come at a huge payload penalty, so the cost per kg would go up, not down. Now the fairing reuse. First the R&D should be orders of magnitude cheaper than developing a reusable first or second stage. SpaceX has already reused one single fairing 20 times, and the limit hasn't been reached. But in fairness, a few fairings were lost. Still, it is a good number. They were able to catch several fairings, but than decided that, they can let them fall into the water. Together with over 400 reused fairing halves, it gives a clear indication that refurbishment isn't a big hurdle. With 6 Mill. for a full fairing, a good number of reflights, low cost for refurbishment, it comes down to the fixed cost vs cadence of the rocket. I have a hard time believing that the fixed cost are beyond 12 Mill. per year, but I really don't know. And with than I don't get it why Ariane 6, Vulcan, New Glenn and Relativity Space aren't jumping on it. They all want to fly quite often. With 5 flights per year they should look into it, or not? My guess is also that smaller fairings get more damaged during reentry than larger fairings, so everything below 4? meters in diameter is too small? So yeah, I'm beyond what I can really answer when it comes to those things.
Love the question. I'm going to be dropping a video in the next few days asking for questions from people, and if you copy your question to a comment on that video, I'll consider it. WRT second stage reuse, look at the video I just just dropped. Full reuse the way starship is doing is is ridiculously hard to do.
When you throw out a bunch of factors, and do the math only on the one you consider important, you can easily arrive to incorrect results. With increased gravity you will also have thicker and deeper atmosphere, for instance.
I did assume that the other factors change at the same rate, so they aren't ignored, but as I said, my answer is wrong, but it's still useful. Drag losses just aren't that big, and scaling them is probably fine. If you want to do some numbers, I'd be happy to find out how wrong I am.
I would interpret the data a bit different and change the conclusion to "Starship type full reuse is imposable." Switching to 3 stages akin to Von Braun's Ferry Rocket, using carbon composites, and using drone ship landings all would reduce the payload hit that the increase gravity causes as the falcon 9 data shows.
One thing you're ignoring is the fact that orbital velocity also depends on gravity, so you'll also need more dV for higher gravity or less for lower gravity.
was about to comment the same thing. it's way more complicated than just pretending the rocket is 10% heavier chatgpt says 400km LEO speed is ~7650m/s and 400km LEO speed with 10% gravity increase (same size planet) is ~8050m/s. so roughly a 5% increase. still, neglecting this extra dV, neglecting extra gravity loss and extra time to fight that increased gravity loss, neglecting thicker atmosphere seems like too much of an oversimplification..
@@jrherita you're right, I missed that somehow or maybe I thought that's the equivalent dV to reach normal LEO speed with a 10% heavier rocket. at least 5% seems to be correct. intuitively though, seems like 10% in gravity increase should mean way more of a penalty than what's calculated in the video...
The point was to come up with a gravity factor and use that as a multiplier for the entire cost of getting into orbit, so it's basically assuming that all the factors that control the overall delta v scale at the same factor. That is obviously wrong - the factor will be different in for different costs - but it's directionally correct and simple enough to be explainable. Producing a more robust calculation is left as an exercise to the viewer...
Seems like a good augment for a set of semi reusable solid rocket boosters; ULA style.. But for StarShip, that would require a whole different pad design. Also consider that StarShip units in the future will not be returning and that maybe the tanker design yet to come (, maybe they can cut a hole in them and fill them up with heavy asteroid chunks in the future after rigging a 'space sail' onto them).. Hey, did I get a laugh?
These calculations were for 400 km LEO. Did you account for the thicker, denser atmosphere that might be expected to go with higher gravity? 400 km might still experience too much drag to be stable. Also what would be the situation at Venus with its earth gravity but 90 atmosphere surface pressure?
Fascinating, so, the 'impossible' bit would probably come from the increased orbital velocity necessitating an ever heavier heat shield. Another example of how god got earth 'just right', or was it the mice? I cant remember.
I liked your recap. 2 questions. did it take into account 1) Falcon's second stage is not reusable where Starship is. 2) fuel to land with - meaning I saw the getting into orbit, but also landing fuel? - I could have missed it. I also like your style and use of graphs. good work :)
Yes, I estimated how much delta v I thought a fully reusable starship would require. It's more than Falcon 9 but starship requires minimal fuel to reenter - just enough for the landing burn which is pretty minimal. It's dwarfed by the extra weight required.
I subscribed to this channel for interesting calculations, and I think other people did too, so if you do a more detailed analysis with more factors it would be very interesting
I did a similar evaluation from different principles. I started with the assumptions of same planetary density (which is reasonable as Mercury and Venus have similar densities, and yet still is a very good case as Earth has the highest density of any planet in the Solar system), and similar atmospheres (ie I could ignore drag losses). From that I got changes in orbital velocities at 400km altitude that nearly exactly align with the change in gravity. 0.9g was just under 90% velocity, 1.1g was just over 110%, and even 2g was just over 200% velocity. I also assumed small changes in gravity losses making the change in required dV closer to 89%, 111%, etcetera. With a similar Falcon 9 model, that translates to ~13,000kg to 400km on a 1.1g world, and ~30,000kg on a 0.9g world. I also got an SSTO payload for Starship of nearly 20,000kg on a 0.9g world, though that doesn't allow for a propulsive landing, full reuse would still require 2 stages at 0.9g. It was also interesting that, assuming a commensurate increase in thrust (to avoid horrible gravity losses), expendable Falcon 9 could probably reach orbit on a 1.5g Earth (with ~1.5 the diameter as well). A 2g world is extremely unfavourable for chemical rocketry, requiring somewhere around 19,000 m/s of dV to reach low orbit, and I may have significantly underestimated gravity losses. I think it is possible, but only with very efficient structures and lots of stages.
Typo: At 0:32 you write "how would increased gravity effect rockets?" "effect" should be "affect". "Affect" (to influence) is a verb, and "effect" is both a noun (the result of the influence of something else) and a verb (to manifest with intention). Its verb meaning is only rarely used, and it's clearly not what you meant here.
Isn’t the starship( with booster) mass fraction to orbit something like 2 percent. It doesn’t sound like it would take much more gravity to make that zero ?
Op knows the difference, but contrary to popular opinion, op is not a robot and therefore sometimes make makes mistakes. A book editor I was writing for once told me "don't let 'perfect' be the enemy of 'good enough'" and I've found that to be sage advice.
Yep, but you all missed the real point: higher gravity, requires the rockets to be more robust, so they weigh more. And to carry more propellant, which makes the rocket even bigger and heavier... Yep, in higher gravity your Earth rockets are collapsing under their own weight and on dynamic forces... because you forget what inertia is... Scaling linear the weight means you forget that the force is a power of acceleration... Not to say you never calculate the escape velocity, how much energy will require that escape velocity, and the rotation speed influence, to see how fast you need to fly just for equilibrium... So your calculation did not convince me. I am sure you missed a lot...
Completely missing the point. He was talking about full reusability, i.e. Starship/Super Heavy. The factor most sensitive to orbital velocity is reentry heating. 5% more velocity means about 20% more heat, which likely means 20% more heat shield mass. It would also mean 30% more heat shield weight. Now structural integrity is also completely ignored. If your ship is heavier, it needs thicker walls, increasing mass and weight even further. This has a similar runaway effect as the rocket equation has on dV. Finally, I think he was actually talking about planet mass, not surface gravity strength (this is an actual error of course), more massive planets are denser and have a disproportionally higher surface gravity.
I might be missing something but it seems your energy calculation only accounts for the increased orbit velocity but where do you take in account of the fact payload, fuel and all structures weigh 10% more.
I'm gonna make an assumption before watching the video. Elon is exaggerating "impossible", but reference to the Falcon 9 specifically it would be impossible. With larger rockets it wouldn't. My guess is orbital speeds would be the biggest factor.
Neat to see how super wrong I was. I did see that you missed something, Starship coming in hotter and needing to land with more mass and not just talking about the landing burn, but the actually weight of reinforced joints and landing gear (flaps and thermal insulation) That would more than chip away at that 4% payload.
The factor applies to the whole vehicle and that would include reentry structural requirements since those influence the earth gravity Delta v. I have no idea how the higher gravity actually influences reentry. The factor could be higher or it could be lower.
The earth's rotation at the equator is about 465 meters per second, and the rotation at 28 degrees (cape canaveral) is about 400 meters per second, so it's a small difference - less than 1%. That's assuming you are willing to launch to an orbit at the natural inclination of the site or higher. If the ultimate orbit you are targeting is geostationary, then launching from 28 degrees costs about 400 meters per second over launching from 0 degrees as you need to do an inclination change to get to 0 degrees.
Thanks for thinking that out. However you proofed Elon wrong here and pointed out the problem with Starship. The problem with Starship (just in my opinion) is that the are effected by the reentry heat is too large which adds "kind of" unnecessary mass to it. So I'd suggest that a design with less area exposed to reentry heat would be easier. In other words I favor a landing capsule design --- maybe like Stoke space etc. The heast shield for the next test fligiht is going to be heavier I'd say SpaceX official defined the heat shield as purely experimental.
Less area for a given mass may mean higher re-entry heating. I have a video where I talk about stoke. It's not clear if their design works at all, and starship is ultimately designed for Mars.
@@EagerSpace I think the basic idea behind the landing capsule design was less area exposed and the hot air escaping in a way the upper part doesn't get hit by the hot gas. I suppose it is a kind of simple concept because it is used so much for reentry. Probably some kind of automatic flight stabilization too. Reminds me on some kind of roly-poly or wobble doll.
The "Qoute" from Elon could have been from me ;-) Of corse I sayconfirmed! I always said: "Rockets have so little payload and need so much propellant, that it would be impossible to make rockets that have any payload to orbitals, if the Earth would have some significant higher acceleration of gravity. It is not very importand where the threshold is, at 5% 10% or 15% but its obvious for me that this around 10% by simple reasoning. If you need around 90% of the weightt of the rocket for propellant, then it is a good first guess, that you need around 100% propellant at 10% higher gravity force. So this a simple and not correct calculation, but good enough for a estimation. With diffferent technology like maglev-ramp it might be possible at double earth gravity, but not with chemical based rockets as used nowadays.
When Elon says impossible at 110% gravity he means full reusability at scale (starship) is impossible for MARS. At that gravity, it would take 100s of tanker flights to refill one starship for MARS. Now answer is it super easy at 90%.
Probably not impossible but not economically feasible. Starship was after all optimized for earth gravity and a compromize between cost and performance. With enough money it could be made out of carbon fibre and use hydrogen to reduce weight and increase isp - but stainless steel and methane are able to get the job done cheaper and the performance is "good enough"
I'm very interested in seeing what Neutron will be like because Rocket Lab is the master of carbon fiber. I think the performance is going to surprise a lot of people. I think carbon would have been a disaster for starship. Starship is really easy to change because you can quickly modify a stainless steel design, but carbon fiber requires new molds and that's a ton of work. There's also the transportation aspect - Starship is hard enough with the factory just down the road from the launch site, and their original plan was to build starships in LA and then ship them to Boca Chica. No way would that work. I'm not excited about hydrogen for reusable rockets; the second-stage tanks are so much bigger so you are adding a lot of dry weight to the system.
The advantages of hydrogen quickly disappear when the entire ship needs to be returned, huge tanks would increase the diameter of an already thick ship, along with its mass, which cannot be discarded, carbon fibre not good for cryogenic fuel and not good for re-entry and reuse
I could've sworn when watching Musk's gaming stream that he said it was 20% higher Earth gravity that he said was impossible. But maybe I misremembered while watching him play DIablo IV with a bunch of teenagers.
There is no way this calculation is correct. If you add 10% more gravity, then that is comparable to adding 10% of the fully fueled rocket as payload when on the launch pad. Not just 10% more payload.
No, that's not how the rocket equation works. Your mass at stage shutdown is unchanged. In terms of the required liftoff thrust, you are correct that it would be equivalent to adding 10% extra mass, but what happens after liftoff follows the rocket equation.
Yes i was thinking this too. You would need extra rocket engines to lift off adding way more mass along with a stronger frame to deal with the extra thrust. F9 produces 7.6MN of thrust and at lauch gravity pulles with 5.7MN giving a positive thrust of 1.9MN with one G. If everything now weights 10% more gravity will pull with 6.3MN leaving only 1.3MN of thrust a 32% loss. This effect componds gravity losses as you are accelerating a lot slower now.
Is claim about version 2 , starship I think is wrong, it is only slightly bigger, but to carry 100 tonne of to orbit, starship needs to be twice it's current size . How much exactly ? So currently fully stacked starship weight 5000t , and most likely can carry 50 t to orbit . 50×100/5000 = 1% , only 1% of it's mass is carried to space . So to have 100t , there need to be 10000×1%/100 = 100t . This starship needs to be 10000 tonne heavier to actually achieve those numbers. Version 3 of starship I'm not sure how large it needs to be since the trust has increased.
This is completely wrong. The percentage will change with the size of the vehicle. Bigger vehicles are generally more mass efficient. Twice the size might give four times the payload, or more, or less. It depends on the specifics. Regarding Starship, the changes between versions are not just to make the vehicle larger. There are also changes like integrating the hotstage ring, removing heat shielding on the engines (as the engines will be more robust), increasing thrust-to-weight on the engines, shaving off excess weight all over the place, etc. The current version of Starship is very unoptimized. SpaceX will focus on optimization for the next few versions, once they have a minimum viable product.
@@SpaceAdvocate they did say the trust would increase, so I guess there would be some improvement although I don't know how much . How does increasing size increase efficiency?
@@m.c.4674 One basic thing that increases mass efficiency is that most of the mass is in the surface of the vehicle. This means that the mass of the vehicle is strongly correlated to the surface area of the vehicle, rather than the volume. As an example, the formula for the circumference of a circle is 2 * pi * r, while the formula for the area is pi * r ^2. As you increase the radius of the circle, the area increases much faster than the circumference. This is the same for the volume of a cylinder, as well as many other shapes. The volume increases faster than the surface area, as you increase the size. As an example, if you have a 9 meter diameter, 20 meter tall cylinder, and double it to 40 meters, the volume goes from 1272 cubic meters to 2544 cubic meters, or an increase of 100%. While the surface area goes from 692 square meters to 1257 square meters, or an increase of 82%. Other things that increase efficiency for larger vehicles is that some components don't need to be any bigger for a larger vehicle. Like the avionics. You can often use the exact same avionics for a larger vehicle than for a smaller vehicle. There are many components like this, which do not need to be any bigger for a larger vehicle. One big example for Starship specifically is that it's unlikely that the future version will have a bigger payload fairing. The current payload fairing is plenty big, and can accommodate a 100-200 ton payload. This is like 40% of the length of the Starship upper stage which doesn't have to change at all.
@@SpaceAdvocate but it is increasing in length , even if it wasn't drag also increases with diameter , about the same as volume. Computer , sensor in a ship this big is already microscopic compared to the ship . And structural support will need to increase as the mass increases. I'm a space x fan , I just want actual proven numbers on the payload that starship new raptor engine can lift to space . 10% more thrust , could be 10% faster fuel intake, or preferably a 10% increase in the speed the gas is being released (I think they call it bar pressure, something like that). Let's say it is 10% more bar pressure, okay so per tonne of fuel 10% isn't used , the rocket is pretty much entirely fuel , so 4500 tonne of fuel , so then the ship will have a remaining 450 tonne of fuel. If 4500 tonne of fuel can only life 1% of payload to space and 450 tonne of fuel is 10 times less , then that 10% increase in bar pressure would total to 1.1 % of mass being payload. So a payload increase of 5 tonne totaling 55 tonne , version 2 I think is about 10 percent longer so that another 5 tonne, so total tonnage of version 2 would be by my approximate 60 tonne. Version 3 is still completely hypothetical, they may never achieve this , or even want to do this , 33 engines and not one ever blowing up, yeah see you in 100 years .those engine shields will remain. I'm am biased in that I don't think starship should do any mission outside low earth orbit. I don't think any of the current rocket engine cryogenic fuel or not is efficient enough to sustainably go to Mars , moon etc.. Ion thrusters are simply better , rockets release gas molecules in slow motion in comparison to ion thrusters. Starship has the payload capacity to low earth orbit to build a true starship, one power by ion thrusters.
@@SpaceAdvocate when it is low gravity or space , using rockets is kinda not good at all . Ion thrusters typically have specific impulses in the range of 2,000 to 5,000 seconds. This is much higher than the specific impulse of chemical rockets, which are typically in the range of 200 to 400 seconds
Also, what do you think about the Elon's mention of our having a thick atmosphere as a contributing factor to full reusability being very difficult on Earth? It's interesting in light of you considering drag during ascent to be so negligible that you didn't include it in your model in this video. In your estimation, would full reusability be easier if we had a thinner atmosphere?
Atmosphere is interesting (and I think very complicated) because, for a reusable vehicle, it doesn't just impact drag on ascent, it also affects various aspects of reentry: how much energy can you bleed off via drag/friction heat, how fast will this happen, how hot will things get, what trajectory do you need to use, what terminal velocity will you arrive at, and so on. And so, depending on what sorts of changes you made to the atmosphere, it seems it could potentially have quite a substantial impact on the TPS design and its mass (or even the extent to which a TPS, mostly-alone, is actually capable of bleeding off the vast majority of your energy during return; and, therefore, whether perhaps you'd need to lean more on rocket retropropulsion etc), which could have big implications for the launch vehicle dry mass and the overall vehicle design (which comes back and affects ascent too). At least for cases with a *substantially* thinner atmosphere, my impression is that ascent would be a little bit easier, but then those gains would be small in comparison to the problem on return of "how the hell am I going to get rid of all of this energy?!" Mars landings are very difficult due to its thin atmosphere: just to land a 1-ton rover, you end up needing very elaborate multi-step techniques involving e.g. an ablative heat shield, followed by a GIGANTIC supersonic parachute, ultimately followed by quite a bit of expensive powered descent. (And granted, the Mars examples we have all involve coming in at interplanetary-rather than merely orbital-velocity; and they're also pretty mass-limited overall for what measures they can reasonably employ for entry, due to not being a giant, orbitally-refueled vehicle; but still, the thin atmosphere makes EDL a substantial pain, I believe mainly because it simply limits how much energy you can get rid of passively via drag techniques.)
@@TimJSwan Cheap propellant is cheap. If they can fly Starship for even $10MM of props and get Booster and Ship back, that likely costs less than expending a F9 upper stage. It should cost much less, to orbit 8x the payload.
@@TimJSwan No - it uses way more fuel. It's based on the fact that fuel is cheaper than rockets, and that by throwing more of the former at the problem, you can brute force the rocket equation.
What was the point of this video? Full reusablity is about cost and has almost nothing to do with the efficiency of lifting a load from a gravity well. If there is a model where chucking out the first and/or 2nd stage were financially profitable I am sure it would have been considered by NASA a long time ago. There is also the question of return trip and ferrying loads to and from destination orbits even if you set aside landing and relaunching of a space vehicle.
Uh... If Earth's gravity is +10%, then orbital velocity at 400km will be faster. More delta-v will be needed. I do not see that variable in your calculation. My gut feel is that Elon is right.
@@EagerSpacegravity is in your equation as a force to be resisted. I didn't see where orbital velocity at 400 km altitude changes with gravity changing. Perhaps I am misunderstanding?
The orbital velocity is sqrt((gravitation constant * mass of the earth ) / orbital distance from the center of the earth). You would get higher gravity because the mass of the earth was greater - either you have a bigger earth or the earth is more dense. I chose the "more dense" option as it was simpler.
"A moving and something exploding target". It's this sort of highly informed precise verbage that has made this you tube channel a must watch for space fans everywhere.
I'm glad that somebody like that comment.
@@EagerSpaceyour calm dilevery added a lot too
Deadpan snark heeds no generational barriers
"Verbiage" is generally considered to be a derogatory term ("excessively lengthy or technical speech or writing") but I get your point and agree! This info was useful with some humor. 👍
@@tonybrock5288 Merriam-Webster: “Verbiage has a second sense meaning, simply, "wording," with no suggestion of excess. This second definition has sometimes been treated as an error by people who insist that verbiage must always imply excessiveness, but that sense is well-established and can be considered standard.”
I feel like it's worth noting that increasing gravity would have other very substantial effects too. first, it'd pull the atmosphere down more making pressure higher. it'd have also probably attracted more gas when the planet was was born, so thicker too. additionally, it'd require more thrust to even get off the pad, let alone efficiently, making rockets bigger and more drag-y. But in addition to that, the first stage would need notably more propellant to land, and not only would this be true for repulsively landing stage 2, you'd also be coming in faster, and coming in faster into a likely thicker atmosphere, making the heat shield way more difficult. so honestly. it's likely the case for starship is even worse than you think in higher gravity.
Well, since the original comment talks about air density too I think it is fair to accept that the comment is 'for a given atmospheric density, 10% more gravity would be a problem'. So no - no one said that 'a planet that formed with 10% higher gravity......'
I wouldn't be surprised if 10% extra gravity would equal multiple times the atmosphere. I can't imagine that result would be linear
Huh... How about DeltaV? Wouldn't higher gravity planet with same diameter require higher velocities to stay in orbit? TWR, maxQ is one thing, but I think DeltaV would be really hard. Look at difference in DeltaV requirements between Leo, MEO and GEO. F9 can lift 20+ tones to Leo, but 8.5 tones to gto. So if you would need as much deltaV to heavier Leo as currently to gto, probably you wouldn't have any margin for recovery.
@@just_archan ultimately needing a higher twr at lift off means you get less fuel to build horizontal velocity. so yes, you need more delta v to start with, but twr further compounds that issue.
@@etherealswordsman3214 I don't deny TWR issues, but more important imho is amount of propellant that rocket have to carry
This channel is by far the best rocket/space youtube channel.
0 artificial drama, high level technical content, just how I like it.
Thanks.
RUclips is not the place to learn rocket science this video is radically oversimplified but it’s correct starship is a serious payload problem. If you really wanna learn this and the complexities of what it really takes with different types of vehicles, get a copy of explain and some textbooks on aeronautical engineering, and Space exploration
Wouldn't higher gravity tend to disproportionately increase gravity losses? Saturn V, for example, only had 1.15 twr, which would drop to 1.05 with 10% more gravity. Which means off the pad 67% less work being done.
This is roughly speaking intentional, since engines are expensive and gravity losses aren't large enough that you should overprovision them, whereas fuel is comparatively cheap despite diminishing returns. A Saturn V densely packed with Raptors could have an incredible T/W.
Yes. But the factor I used applies across across the full cost of getting to orbit, which includes drag and gravity losses.
So it's not really true that I'm ignoring them, I'm just assuming they scale at the same rate as the velocity energy does. Which is, as I noted, obviously the wrong thing to do.
More than fair. My instinct is that the "real" answer is probably even more exaggerated than this good approximation suggests, rather than less exaggerated. I think gravity losses would not scale linearly could contribute, but I haven't done that math either.😅
@@darylbardo Gravity losses aren't too large with Starship. It has a T/W of around 1.5 at liftoff, so even with 1.1 times the gravity, the T/W would still be pretty good at something like 1.35. You could also expect that a Starship designed for higher gravity would have had more engines and higher thrust.
A Saturn 5 designed for 1.1 times the gravity might have had six F-1 engines. The penalty would primarily have come in the form of added dry mass, cost and complexity, while the reduction in payload would have been modest. The gravity losses may even have been reduced overall, by adding the sixth engine.
Astronauts have a maximum acceleration, gravity is part of that accelertion, so T/W ratio couldn't be increased to compensate for increased gravity. There is also a matter of max Q which limits the early T/W ratio even of unmanned launches. With increased gravity you would also get a denser atmosphere further effecting max Q.
Who else were here when (unedited) 😂
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any cool behind the scenes stuff? He was quick the the reupload
I think you can figure out that I mess up the lines sometimes, that I sometimes rewrite lines on the fly, and that I have a dog who sometimes walks into and out of the room.
I don't think I swore in this one, but sometimes that happens when I mess up a line for the fourth time in a row.
@@EagerSpace when you first posted the video I was writing out a comment but couldn't post it because you took the video down. Jokingly I suggested an alternate title; "How the Sausage is Made - Is Elon Right?"
The other possibility is that he's also talking about economically impossible.
Robert Foward proposed all sorts of ways for an intelligent inhabitant of a neutron star to get into orbit, which is obviously much more extreme.
So there's ways of doing reusability, even from a much more than 10% higher gravity, but they're impossible if it were to require the entire industrial output of the planet to achieve them.
It also hints at Starship having marginal economics.
@@saumyacow4435 I'm sure it is. We've had spaceflight for nearly 70 years. The first commercial passenger flight was only 7 years after the first powered flight.
It's obviously very hard to do this economically.
no, Elon quite literally meant impossible, the assumptions in this video are wrong, you can't assume a linear increase in parameters when your distance is squared.... delta V behaves like an exponential curve, same with gravity drag, with that alone you get a required fuel mass to get payload to orbit of over 99% of the weight of the whole rocket system
getting anything to orbit with rockets becomes impossible
@@ivant5054 well you could use a ring fountain for instance. That would work, but it's not economically feasible.
@@ivant5054impossible (or at least impractical) with chemical rockets, yes.
So close to forcing Project Orion into existence. Damn.
I saw him say that quote (Ellie in Space, I think) and wondered if anyone would make a video on it. So glad you did!
1:30 Misconception here. When you add up E_a and E_v, your resulting energy is going to be the same, whether you burn up before burning sideways, or do an optimized gravity turn. What changes is the gravity losses, which a gravity turn minimizes.
Your equations don't "assume" that you go up and then sideways. It works for both scenarios. That detail is hidden in the γ in gravity loss. γ (pitch) varies over time and depends on the specific trajectory that you take.
A gravity turn minimizes sin(γ) as early as possible, which happens when the craft turns sideways. So more energy will be put directly into E_v initially, but gravity will exchange that for an equivalent amount of E_a as the altitude increases.
In the end, for the same destination orbit, you will get the same values for those two energies no matter what ascent trajectory you use. So it's entirely correct to add up those two values; there is no assumption about the trajectory baked into them.
Your ultimate point is still right though, we need simulations to optimize the losses
Yes, I made a *hell* of a simplifying assumption, but I think the answer is at least directionally correct. Building the right simulation for a specific rocket without knowing the real numbers nor knowing the actual flight path they plan to follow doesn't seem very tractable.
Tried to explain why it was a terrible idea to visit a super earth to someone. We would be jelly spots.
:0) Jelly Spots, a kinder humanity!
And even worse, leaving the planet would be impossible
@@mostafamohammedahmed3404not with nuclear rockets.
Wouldn't more gravity also constitute a thicker atmosphere thus changing how they would have to deal with Max Q throttling or the early stages of flight in general? Also, with that in mind would the overall air frame of the vehicle have to be more robust, leading to a heavier rocket?
I think the answer to both of those is probably "yes".
Definitely. It would have a much higher altitude to its "edge". it would be more dense where it matters most, plus our entire current atmosphere after that. there may be some aspect of lift from the extra density that would compensate in some way. I'm also not quite sure what percentage it would add to atmospheric density relative to 10% more gravity.
The difference in more gravity & how different the physical characteristics of the vehicle would have to be, is kind of a mute point, because it likely would mean that we would either be somewhat different developmentally/evolutionarily or life might not of even emerged.
Heavier planet ≠ thicker atmosphere. See Titan Vs Earth, or Venus Vs Earth.
@@matthewkantar5583 Those all have vastly different circumstances. A better comparison would be:
Titan: M = 135 Et, P = 147 kPa
Triton: M = 21 Et, P = 1.5 Pa
Pluto: M = 13 Et, P = 1 Pa
Similar densities, internal structures, temperatures, and atmospheric compositions.
Yeah I would imagine an increase in gravity as massive as 10% would have second order effects on the circumference of the planet, the rotational speed, the volume and density of the atmosphere, etc...
If I had to guess, in that case 400km would literally be impossible for LEO in a planet like that and could be more like anywhere between 450-500km on the low end.
Then you would have third order effects on the heat shield on the way back that would need to be much heavier because of the increased LEO speeds and the greater gravity increasing acceleration, which itself makes the ship heavier and necessitate more hardware to cope with it, making it have an exponentially greater cost on the design.
You keep stacking design, gravity, drag, reentry, recovery, etc on top of each other and you can see how bad it can get.
At the same time if you imagine something like 80% gravity, instead of starship we would probably already have a 1 kiloton to LEO fully reusable rocket that is flown every couple of minutes out of pada around the world like a plane does today.
I did a little research there and then I was happy that Elon only spoke of gravity so I got to assume the same size earth with higher density.
With higher gravity the atmosphere would probably be thicker and I would guess the extent would be different too… that could matter for reentry… maybe?
I was just getting ready to comment this same question.
Go back and watch the part where I talk about "simplifying assumptions"...
I think the answer is that atmospheric differences matter but not a lot.
@@EagerSpacewell maybe not for launch but reentry i see two key differences
Im guessing smaller flaps would be needed
But you would need more robust tjermal protection im thinkin tps would cost more in terms of weight then the flaps would save but have no way of checking how big of a penalty that would be
@@yakirfrankoveig8094You could just reenter at a higher altitude with the same air density. The 10% faster orbital velocity would be an issue since it would increase temperature by ~21%.
@@kolbyking2315 yeah i considered reentering higher when i wrote that comment because you enter at the same air density but at a faster speed so you would experience more heat from the begining as you said and it would also persist throught the whole regime since you will also be slowing down quicker and therfore dropping faster into thicker atmosphere than you would on earth
I told my son. "Avoid youtube. " so he found your Chanel and I have to concede. It's very informative and well thought out. But you don't need me to say that. Great content.
It would be interesting to see other rockets' Payload Effect of Different Gravity charts. This also makes me curious about the comparative difficulties of Lunar vs Martian launch vehicles.
My guess is that the expendables are going to have roughly the same shape as Falcon 9 does; definitely true for Vulcan.
I think a "payload versus delta v" chart is a bit more interesting and relatable.
Lunar and martian both require a lot of delta v and it's not that far apart, so you need the same sort of vehicle for both.
Starship is planned to be single-stage to Earth with no refilling, so that .38 gravity multiplier is doing some work.
Mars is ridiculously easy to get off of.
@@EagerSpace So is the moon. Apparently you could manufacture Aluminium structures like girders and plates and throw them into LMO from surface, to build space stations and large spacecraft. No need for on board propellant. The moon could be quite a good ship building yard! What do you think?
@@EagerSpaceOh, I forgot to say how much I enjoyed your video. Keep up the good work!😊
Ignoring drag ratios for simplicity was necessary, but it's likely most of where the rest of the "10% is impossible" idea comes from. Of course, Elon is very much one for hyperbole, but still fun to think about.
If the earth's gravity were 10% higher, it would stand to reason that the atmosphere would be shorter, and thicker at the bottom. that means that not only is the thrust to weight ratio going to go down from, for example, 1.5 to about 1.35, there would also be greater drag losses in that early stage of flight. wasting 2/3 of your fuel fighting gravity vs wasting 3/4 sort of thing.
the booster's delta V would be impacted quite a bit, and if it were aiming for a boostback it'd need to keep more propellant for it's landing and hover. that could take the payload down another 2% easily, and like you said, starship's only hauling 4% as it was and lost the first 2% to the increased orbital velocity.
Nice video, hopefully it makes it easier for people to see that elon isn't just waffling lol
It was interesting to see the raw take.
That was about average for my raw takes; it was a retake this morning when I finally figured out that the last one had a disk error in the middle and was unusable.
@@EagerSpace You should put raw takes as patreon exclusive (jk)
That would seem to be a disincentive to joining...
Ignoring drag is where you are going wrong because the acceleration can't be linear due to forces on the rocket at lower altitudes, remember they need to throttle down to go through max Q to make sure the forces at max Q aren't too high, that is how significant the drag forces are. This is most significant at the worst part of the trajectory when the rocket is still really heavy with fuel. Also as gravity increases so does atmospheric density so at higher gravity the effect is even worse. Also higher gravity means you need to go higher to get above the atmosphere in order to achieve a stable orbit that doesn't decay too fast. There are many factors you ignore which validates Musks comment to a far greater extent, though even your univariate analysis shows it right on the edge of feasibility.
A higher gravity doesn't increase the amount of atmosphere. It just increases the density at sea level, while the density drops off faster for higher altitude. The rocket still has to get through the same amount of atmosphere, it just gets through more of it at the start, while it is is moving slow.
I think the situation with drag would be improved, overall, if the vehicle is designed for the same TWR. You would clear the densest part of the atmosphere quicker, and you could perform a more aggressive gravity turn.
Also we dont take into account other factors that come from that like sea level thrust in a higher density atmosphere or higher drag to to the hypersonic speeds(speed of sound is lower). So everything points to how much harder this would be.
Drag loss is low, typical around 100 meters per second, or only about 1% of the total energy cost to get to orbit. Rockets just aren't moving very fast down low and they get above the atmosphere fairly quickly.
See web.stanford.edu/~cantwell/AA284A_Course_Material/Karabeyoglu%20AA%20284A%20Lectures/AA284a_Lecture7.pdf
@@EagerSpace But what I am saying is that forces due to drag mean that the rocket has to be throttled back in the lower atmosphere operating at below peak efficiency. As with all these things, one small effect impacts many others which in total equal a much larger total impact.
I'd add/nitpick only 2 things:
1: as the rocket equation gives out m/s as a unit and specific energy is m²/s², you'd have to take the square root of your energy multiplier (assuming the value is accurate); and
2: It'd probably be more accurate to say "a x% reduction of the stage's mass at the end of the burn" instead of total mass. So, because falcon's payload represent more of the stage's final mass, you could cut a third of it off and still have half of the payload mass, while starship would lose all of it.
Overall, the effect would be very similar, but I think the intensity would be significantly reduced.
1) Perhaps. See "simplifying assumption"
2) Yes.
It's not just the mass of the thermal protection that directly subtracts from payload mass. Its also the mass you have to add to the second stage such that it will survive the structural loading of re-entry and landing. Rocket Labs did their sums and concluded that a non reusable second stage for Neutron makes economic sense because all they are throwing away is one very light tank (about the mass of a large motorcycle) and one engine. Starship is struggling because it keeps having mass added. Now Elon is talking about more robust (heavier) tiles and an underlayer of ablative material. This was a vehicle originally touted as having a payload to LEO of 150 tonnes.
There's another video in the works that will dig into this a bit more.
I haven't done any numbers but I suspect the loading on ascent when it's full of fuel is much higher than re-entry when it's empty. It is in another direction.
I am interested in how neutron turns out because it's the optimized partially reusable rocket they SpaceX didn't try to build, and I expect the economics to be good.
Starship is ridiculously hard to develop, but Elon's goal isn't lift to Leo, it's Mars.
@@EagerSpace Fuel and tank pressure on ascent will load the walls of the vehicle uniformly and in tension. In descent you've got several things happening that aren't in your favour. Firstly, the dynamic pressure is high - it's equivalent to hurricane force winds. So you end up with higher g forces overall. Secondly, the flaps act on their hinges and the forces from the flaps are then transmitted into the whole structure which is now being torqued - basically it's like pipe bending. You get a bunch of internal elements that want to buckle as a result. Thirdly, on launch you get internal pressure that actually stiffens the structure, but on descent you've got empty tanks and lower pressure. And fourth, you saw the flapping of the steel sheets on the upper sides of the flaps? That's aerodynamics kicking in. It's basically a cylinder doing a belly flop. there's going to be places where the stream separates and turbulence kicks in. So the steel walls will react by flexing or going into vibrational modes. That in turn will react with the dynamics of the gas stream, possibly creating feedbacks. Bottom line here is that there's a lot of movement going on that is trying to shear and separate the tiles.
Tiles can work if you've got an absolutely foolproof way of ensuring they don't crack and don't tear out of their mounting points. I think what Elon is now doing is going for denser (thus stronger) tiles, but there's an obvious price to pay for that. I also have doubts about the ablative underlayer, if its silicon based. It's not that that stuff can't survive high temperatures. Rather its the combination of temperature, charring and then high dynamic pressures and turbulence. See Orion's heat shield. One of the nasty things about plasma is that if its focused by geometry and then comes back to touch something, it's very destructive - a cutting torch.
To be honest I was feeling better about this when SpaceX announced it's original intention to have transpirational cooling. Yes, it would be experimental but they could have advanced the state of the art quickly. Maybe arrived at some kind of hybrid with a slowly ablative (reusable 10x) material in certain places.
And if you want to know what I'm thinking. I'm thinking what happens when we get a stretched version of Neutron and Rocket Labs starts thinking seriously about a reusable second stage, Stuff like a combination of methane cooling for the engine and ballutes for drag, maybe?
For your next video, could you calculate the calibration factor for correcting "Elon Time"?
That would be funny. It would be a pain to gather the data, however.
The interesting thing on Elon Time is that if it's less than 2 months, it's pretty much 1:1. At least in some cases.
"we add these up and we get a very precise answer that's wrong..." 😂
Great videos. I love your calculation based approach and the types of questions you dig into. Thanks a lot! I hope that your channel gets the amount of viewers it deserves.
Thanks.
Also 10% higher gravity well probably requires more structural strength, so the empty mass goes up a little more for both super-heavy and starship. Cuts into both payloads even more.
Higher gravity would also cause denser atmospere what means more drag and less efficient engines,
so even less payload!
MECO at 5600 km/h on Starship vs 8000 km/h on Falcon 9 means Starship have 1/2 kinetic energy thus more fuel is needed to reach orbital velocity.
Starship should try to land on the Drone ship too.
Yes, but staging earlier reduces the cost of the boostback burn and means that super heavy can give more Delta v to starship. The tradeoff is complex.
And yes, a drone ship would make this a lot easier, but it gets in the way of the operational goals.
For some reason I kept this video open in a tab with the intention to write that you and Suchomimus are closely competing for the "best jokes casually being dropped in videos" award in my mind
Thanks. I need to spend more time looking for the jokes.
Remember when the US had a (almost) fully reusable and pretty reliable rocket (and yes, I‘m talking about the Space Shuttle). Didn’t make going to space much cheaper back then.
Intuitively speaking, the sight of the falcon 9 graphs appearing to asymptote to 0 payload capacity makes me think there's some very important factor that's being completely missed, as the extension of the logic of the graph is that Falcon 9 could deliver some marginal payload to orbit... from the event horizon of a black hole.
It's not quite asymptotic...
I think it gets to about 13,000 m/s of Delta v at zero payload.
Saying it's "impossible" may be a bit hyperbolic, but practically speaking, 25t to orbit for a rocket larger and more powerful than Saturn V is... pretty horrible. Barely more than an expendable Falcon 9, so while you could do it, how reasonable would it be to pursue?
I could see how full reuse anyway might still be desired to lower costs and increase cadence, but it would be difficult up front, and take longer, to send heavier spacecraft in orbit that way.
yes. But even a big ass scale of production of saturn v's would be more expensive than getting full reusability. Because reusability will give you a monopoly that outweighs every throwaway system. The upfornt cost for digital computers and data handling was absolutely astronomical, until it replaced it by orders of magnitude.
I am not an Elon fan either, but this nut needs to be cracked someday. And I don't even think it's going to be Starship, cause the larger you go, the actual better reuse performance you get out of your rocket. The refueling situation will likely be Starships actual killer. Even if Startship is working perfectly, needing a shit ton of refueling missions to perform the actual mission isn't really practical and economical.
And 25t is with my model, which ignores a lot of factors that probably make it lower. There's a biggest discussion to be had, but that will have to wait for the next video...
@Skukkix23 Oh, definitely. Reusability would still be better in the long run, but how would pursuing it be different if it was already difficult to send large payloads to orbit by expending the vehicle?
Requiring megarockets to put comparatively meager payloads to orbit may make reusability seem not worth it for a longer time. Astra's idea of 'mass producing' expendable rockets might be pursued instead for a while, attempting to lower costs and increase cadence that way until they hit a ceiling.
@@davidk1308 Yes, I am very much of the opinion of "right tool for the task". And really a lot of stuff would not even require a falcon 9. Just a really cheap rocket would do the trick also. But I am not even remotely qualified to talk about numbers or economics here, also I wouldn't want to come across this. As @EagerSpace mentioned, even 25t is probably generous.
I just think full reusability will be a bigger step than actually like discovering a new continent. When you suddenly knew, that there was a new continnent, basically everybody already had ships and the means to travel there. The nation or corporation to get the leap on reusability, will have an exclusive wormhole to multiple new continents. This is highly underrated everywhere you look. Because that continent is maybe not even a different landmass, it's actual economical maneuverability in space. The only reason why we're not more in space is now just a scalable function of cost, not a function of engineering.
@@Skukkix23 Having reusable second stage doesn't make sense ( as you said ) unless it's absurdly big to make use of economy of scale ( which Starship might qualify as ) and only haul stuff to LEO and then come back. When trying to go beyond LEO as is the case with Artemis it's incredibly inefficient which was also the case with Space Shuttle.
This analysis is completely wrong and missed multiple extremely important factors.
Besides the increased energy to get into orbit, the rocket itself weights 1.1 times as much. A fully loaded Falcon 9 would weigh 1.1x its current weight, which is about as much of its current payload capacity. The thrust to weight ratio would also be far worse as the engines would get no more powerful, meaning that it spends more time fighting gravity rather than converting its propellant into orbital motion, further decreasing efficiency. Combine that with the increased velocity necessary for orbit, and the payload to orbit of a Falcon 9 on a world with 1.1G would be negative (even just considering the increased wet mass). It couldn’t get anything to orbit, let alone a slight decrease in its current capacity like this video claims.
It would essentially be like strapping a 15 ton block of lead to the top of the Falcon 9, while also expecting it to have increased final velocity. (The Falcon 9’s dry mass is way more than 4t btw.)
This. With those calculations F9 could make it to LEO with 2x gravity lol. People don't appreciate how on the edge everything is for a rocket, for that to be even a comparison you need 10% more thrust, 15-20% stronger airframe, and proboly 30-50% extra full (as a guess its probly even worse). So F9 couldn't make it to orbit with no payload.
@@R0nBurgundy It’s a good reminder that just because a video has a lot of views, and a lot of people agreeing with it, it doesn’t mean it’s remotely right.
I get the feeling from these numbers that we're forgetting that orbital velocities, atmospheric depth and density, and actual effective low planetary orbital altitude all will differ with changing gravity. I'm pretty sure that is the context in which Elon is making his assertion.
The orbital energy term is the measure of orbital velocity.
There are certainly other things that were ignored
TWR with 10% more gravity is: Nominal F9 - Launch- 1.28TWR, 10% more gravity 1.15TWR, this results in more time ascending, more time in atmosphere, more drag, overall slower acceleration = failure to reach orbit. Tried this in KSP-RSS with F9 and it's borderline impossible. Your data needs to be revised.
Purely on DV is possible, but the time thrusting is too long.
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If gravity was 10% higher, the Falcon 9 might have been a Falcon 10.
Or more likely, it wouldn't have been stretched as much. Keeping TWR at an acceptable level but also reducing the payload capacity.
@@SpaceAdvocate Yeah, true, but you'll have put additional fuel if you need to burn for the same duration. Rocket equation is a b***h. Guess it's good think that our gravity is 9,8 not 10.78 m/s/s. Off to try Falcon 10 :)
It might have been interesting to put in the space shuttle for comparison too. I would imagine it fares similarly poorly to Starship.
There is one extra consideration as well that you omitted: On an Earth+10% gravity planet, even the reduced payload rockets couldn't fly. They have the deltaV potential. But they don't have the thrust to accelerate as fast against the increased gravity, so gravity losses would increase a lot. To resolve it, you would need to increase engine thrust by 10% too. For example adding an 10th engine to the Falcon 9 (and renaming it to Falcon 10), which comes with the empty weight penalty of 1 more engine, further reducing your payload.
So in reality it's probably worse than your numbers might suggest.
It really depends on what you mean by "10% higher gravity" and what factors you include in that.
If we reduce Earth's radius to 6074 km, that should do the trick, but adds less than 200 m/s dv to orbital velocity while compressing the height of the atmosphere, allowing you to perform more aggressive gravity turns and reach the top of the atmosphere equally easily to on Earth.
On the flip side, if you add 26% to Earth's mass while composition is held constant, you end up with ~675 extra DV required.
If you inflate the Earth while holding density constant (reducing compositional density by 3.2% in the process), you get a nasty 790 m/s increase.
However, it should be mentioned that habitable planets, super Earth's, not mini-neptunes with thick helium envelopes, can definitely go beyond 10% higher gravity. A 2 Earth mass planet with a composition 20% denser uncompressed than Earth would have slightly over 1.5 G and an orbital velocity of 10 km/s. Worse still, just because it doesn't have 1000 bar of helium or something doesn't mean it has none, and even a bit of helium is gonna be enough to make that atmosphere very, very tall, forcing rockets to climb way way way up to get out of it.
Very intresting
I am ironically of the opinion that a higher gravity environment might be beneficial for space travel, even if it spells hell for reusable chemical rockets.
The reason is Project Orion. If you live on a planet where chemical rockets are literally infeasible, then there is a greater impetus given the same level of drive for space exploration to consider the literal nuclear option. Add in the fact that Orion sneezes at 1 km/s increments in delta-v anyway, and that once you do make it to orbit you now have ion-drive level efficiencies combined with chemical-level thrusts, I honestly think the net result this would have an on a super-Earth's space program would be largely beneficial.
I'd be skeptical that any entity would be willing to cough up the funding for such a project without the proven history of small launch vehicles. Maybe there is a balance point in there somewhere though.
Great explanation! Elon is optimistic on timelines 🧐but rarely wrong on the science...
Probably add the extra bit of heat shields for reentry at +10% gravity, and there goes your 2%.
If you look at the energy requirements from first principles, i would have structured the terms as:
1) Energy that goes into the (dry mass) of the rocket (kinetic energy and gravitational potential of payload and all spent stages)
2) Energy that goes into the atmosphere through friction
And 3) energy that goes into the rocket exhaust.
Functionally, gravity losses are part of 3), you are heating up and accelerating propellant without really adding velocity to your spacecraft. But even in a perfectly empty universe with no gravity, part of the energy used would be in the exhaust cloud, so 3) is more than just gravity losses.
Yes, and you would get a better answer than mine, but I think it would be much harder to explain. #3 in particular seems to break people's brains.
@EagerSpace Maybe, but this sort of analysis would (in my opinion) probably be way to much work to expect from a RUclips video. And, ultimately, the total energy requirements, and where that energy ends up, aren't even THAT interesting. What we really care about is the payload capacity. I think your approach where you look at effective Δv requirements, and assume they scale linearly with the orbit velocity of LEO (sqrt of g) is a very natural first estimate, especially for relatively small pertubations of g+-10%.
I like your rational explanation of my laziness...
Higher gravity means you also need a higher inert mass of structure to support the rocket
Great video, and yes attaining orbital velocity is the biggest fuel requirement, but gravity drag or losses are partly a a factor of time to orbit, the greater the time the greater the drag, hence as weight is greater, hence the acceleration is lower as the thrust to weight ratio is lower over much of the flight which leads to a significant increase in time as lower acceleration figures means longer to get to orbital velocity, added to this the orbital velocity required is higher than earth due to greater gravitational field strength, hence a multiplying of 2 factors. And as you so clearly pointed out any increase the needed fuel mass equates to a reduction in payload, hence according to some models the mass to orbit is even worse.
But once again, thanks for all the excellent videos and in depth research and presentations.
Thanks.
I've talked about gravity losses before - there's a video on them - but it's not very easy to explain or understand, because - as you note - it depends on time to orbit and it also depends on flight path.
The 1st thing is that with a single pad, a fully reusable rocket can only have (1 or) 2 stages, the 1st one returns to launch pad, and the second one has to do a full orbit. This video observes the effect to a 2-stage rocket. If you had a ring of pads aligned around the Earth, then you could have any number of stages technically,. The interesting case is 3 stages, but then when you land the 2nd (out of 3) stage at the next pad, you can't launch again if you don't have a next-next pad (due to earth rotation you only want to launch East-ward). So you want a full ring around in the only inclination that you want to service. Supporting 1 inclination may make sense for Starlink only but even then, you don't have the flexibility to change you mind, this would be hugely impractical if not politically impossible.
Okay, Elon quote confirmed xD
This will be in my upcoming answers video because lots of people have asked.
The two big issues with more stages are:
1) Inclination. You want to launch everything from due east to different polar orbit (though polar might be a different launch site), and so you need a target that you can get to with your middle stage. It will also have different trajectories depending on what kind of launch you are doing (heavy into LEO, light and hot into something higher (assuming you can do that)). You can't get places that work for everything, which means you likely need crossrange capability, which you really don't want to pay for.
2) Super heavy gets by without a reentry burn by being low and slow. Now you have a stage that's coming back faster, so you have a more fuel intensive reentry path.
3) How do you get the second stage back home?
Why is dV just multiplied by energy ratio as if it was a linear function of energy ratio to get to orbit. It seems counter-intuitive to me because the velocity in the energy expression is second-degree
See "simplifying assumption"...
How much do I have to pay you to calculate what a 5 mph, 20 mph and 100 mph starting velocity has as an effect on payload capacity?
95 tons of fuel to get 5 tons into orbit.
That’s 5%
10% increase in gravity means -5 tons to orbit. In other words, it would not work.
One can try designing a 3-stage system for higher gravity, while keeping the materials the same. Second staging around 3-4km/s should be good enough and you can still land on the droneship. This reduces fuel and thrust requirements for starship by about 40%.
How do you get the second stage back? It doesn't have enough velocity to go into orbit so you can't control when it reenters and it may need a heart shield or at least a re-entry burn.
@@EagerSpace similar to falcon heavy center stage - drone ship landing. In this case the second stage will be somewhat heavier than first stage of falcon 9, but starship itself will be somewhat smaller, with, say 4 vacuum raptors.
It would be way farther downrange than the Falcon 9 boosters. A couple thousand kilometers minimum, and maybe far enough that you run into europe or africa.
@@EagerSpace yes, it will be further downrange, similar to the center stage of falcon heavy (staging velocity is about the same).
Another great video. Could you do one about the real performance of Starship? Supposedly current version can launch up to 50 t to orbit, while the next one can do more than 100 t. Two question arise here. How can the first value be so low and what can they do to increase it more than two fold?
There's a video in the works that will deal with that question, among others.
On FT4 starship 2nd stage burned almost all fuel without any payload and did not reach orbit. What is it good for?
The current prototypes seem to be capable of carrying around 40-50 tons to LEO. That's pretty good for a fully reuseable vehicle. The previous record was zero.
Of course, it's less than what SpaceX is aiming for. But they'll keep working on it.
Reportedly both SH and starship were only partially fueled on the last flight.
What an awesome video! thanks for the insight
It'd be very interesting if you could do a breakdown of the kind of rocket/engines required to build a self-sustaining city on Mars (loosely defined as having 1 million people on Mars). If I remember correctly Elon has said that they won't use Raptor for Mars missions, which makes me wonder if they will look into alternate propulsion methods
They will use Raptor and Starship for Mars. Musk has said that long term there will probably be a different engine, but it could just as easily be "Raptor 6.0 Ludicrous Max" or whatever.
The current Raptor engines seem to be good enough to colonize Mars, assuming reliability/reuse is improved over the next few years/decades, and get to an extremely high level. They are already very good engines in terms of thrust-to-weight, efficiency, etc.
@@SpaceAdvocate thanks for the comment!
I don't think there are any practical alternate propulsion methods. There are a lot of nuclear thermal propulsion advocates but they've been saying the same thing for the last 50 years and we have yet to see a real stage. Maybe the current DARPA program will yield one, but I'm not holding my breath on performance.
You might get somewhere with a cycler architecture, at least for carrying lots of stuff, but you still need to get it down to the surface at the other end.
Great deductions, but I didn't see taking into account the atmosphere density with gravity difference. Even now Starship barely survives re-entry. Increasing gravity by 10% should definitely have an impact on atmosphere density too. Reusability might be a b1tch if that is taken into account too.
Terrific video! Nice of you to say that Starship can deliver 50 tons to orbit when, in truth, it doesn't seem to be able to get to orbit (yet) with zero payload.
Both the third and fourth flight got to slightly below orbit with several tens of tons of propellant left over. You'd need to burn around 5 tons of propellant to enter orbit, and the remainder of the propellant could basically be replaced with payload.
The 40-50 tons figure from Musk seems reasonable going by what we can see on telemetry.
The current set of flights were reportedly only partially fueled so that they got the trajectory they wanted.
But yes, they clearly aren't where they want to be yet.
i think this is fine as long as the TWR is still bigger than 1 of the pad, which i think Elon was referring to when he said impossible with 10% more gravity. Really good video nevertheless.
You control twr by how much propellant you put in the vehicle. Higher gravity means less propellant to keep twr the same, so less Delta v.
Our Alien visitors seem to control gravity. Even under water. Couldn't do what they do without it.
Hi, I don't know if You still answer comment questions in your videos, but there are two that are bugging me for some time now (because I can't definitely answer them).
When it comes to cost reductions, is a second stage reuse way less useful than space cadets think?
And why isn't Fairing-reuse more often considered (for new rockets and as an upgrade for existing rockets)?
Here is my very simplified reasoning.
When reuse for the F9 was available for the first time, the F9 costs were 62.7 Mill. $. For a reusable F9 SpaceX talked about 50 Mill., while they kept around half of the savings for themselves. So, around 25 Mill. in savings, and a theoretical price of ~37.5 Mil.
Now the upper stage without the fairing. That way it is a smaller version of the first stage. Instead of 9 times cheaper, let's say it is 7 times cheaper than the first stage (more expensive nozzle...). Let's also be absurdly generous and say, that an upper stage without a fairing could be refurbished and reused as easily as the first stage. Even with that, it would only bring an unsatisfying cost reduction of ~3.6 Mill. And in reality, it would come at a huge payload penalty, so the cost per kg would go up, not down.
Now the fairing reuse. First the R&D should be orders of magnitude cheaper than developing a reusable first or second stage. SpaceX has already reused one single fairing 20 times, and the limit hasn't been reached. But in fairness, a few fairings were lost. Still, it is a good number. They were able to catch several fairings, but than decided that, they can let them fall into the water. Together with over 400 reused fairing halves, it gives a clear indication that refurbishment isn't a big hurdle. With 6 Mill. for a full fairing, a good number of reflights, low cost for refurbishment, it comes down to the fixed cost vs cadence of the rocket.
I have a hard time believing that the fixed cost are beyond 12 Mill. per year, but I really don't know. And with than I don't get it why Ariane 6, Vulcan, New Glenn and Relativity Space aren't jumping on it. They all want to fly quite often. With 5 flights per year they should look into it, or not?
My guess is also that smaller fairings get more damaged during reentry than larger fairings, so everything below 4? meters in diameter is too small?
So yeah, I'm beyond what I can really answer when it comes to those things.
Love the question.
I'm going to be dropping a video in the next few days asking for questions from people, and if you copy your question to a comment on that video, I'll consider it.
WRT second stage reuse, look at the video I just just dropped. Full reuse the way starship is doing is is ridiculously hard to do.
@@EagerSpace Thanks, I will do that
When you throw out a bunch of factors, and do the math only on the one you consider important, you can easily arrive to incorrect results.
With increased gravity you will also have thicker and deeper atmosphere, for instance.
I did assume that the other factors change at the same rate, so they aren't ignored, but as I said, my answer is wrong, but it's still useful.
Drag losses just aren't that big, and scaling them is probably fine. If you want to do some numbers, I'd be happy to find out how wrong I am.
was expecting to click away in 30 seconds... here I'm at the end of the video...
I would interpret the data a bit different and change the conclusion to "Starship type full reuse is imposable." Switching to 3 stages akin to Von Braun's Ferry Rocket, using carbon composites, and using drone ship landings all would reduce the payload hit that the increase gravity causes as the falcon 9 data shows.
One thing you're ignoring is the fact that orbital velocity also depends on gravity, so you'll also need more dV for higher gravity or less for lower gravity.
was about to comment the same thing. it's way more complicated than just pretending the rocket is 10% heavier
chatgpt says 400km LEO speed is ~7650m/s and 400km LEO speed with 10% gravity increase (same size planet) is ~8050m/s. so roughly a 5% increase. still, neglecting this extra dV, neglecting extra gravity loss and extra time to fight that increased gravity loss, neglecting thicker atmosphere seems like too much of an oversimplification..
@@sebastianstan20395:00 he shows delta V increasing due to higher gravity. I think there are other factors though - thicker atmosphere, etc.
@@jrherita you're right, I missed that somehow or maybe I thought that's the equivalent dV to reach normal LEO speed with a 10% heavier rocket. at least 5% seems to be correct. intuitively though, seems like 10% in gravity increase should mean way more of a penalty than what's calculated in the video...
@@sebastianstan2039 I agree - I am also surprised the increase in gravity has less effective than 1.0x
The point was to come up with a gravity factor and use that as a multiplier for the entire cost of getting into orbit, so it's basically assuming that all the factors that control the overall delta v scale at the same factor.
That is obviously wrong - the factor will be different in for different costs - but it's directionally correct and simple enough to be explainable.
Producing a more robust calculation is left as an exercise to the viewer...
Seems like a good augment for a set of semi reusable solid rocket boosters; ULA style.. But for StarShip, that would require a whole different pad design. Also consider that StarShip units in the future will not be returning and that maybe the tanker design yet to come (, maybe they can cut a hole in them and fill them up with heavy asteroid chunks in the future after rigging a 'space sail' onto them).. Hey, did I get a laugh?
These calculations were for 400 km LEO. Did you account for the thicker, denser atmosphere that might be expected to go with higher gravity? 400 km might still experience too much drag to be stable. Also what would be the situation at Venus with its earth gravity but 90 atmosphere surface pressure?
No, I didn't try to account for that.
Fascinating, so, the 'impossible' bit would probably come from the increased orbital velocity necessitating an ever heavier heat shield. Another example of how god got earth 'just right', or was it the mice? I cant remember.
I just worked on the Fjords.
I liked your recap. 2 questions. did it take into account 1) Falcon's second stage is not reusable where Starship is. 2) fuel to land with - meaning I saw the getting into orbit, but also landing fuel? - I could have missed it. I also like your style and use of graphs. good work :)
Yes, I estimated how much delta v I thought a fully reusable starship would require. It's more than Falcon 9 but starship requires minimal fuel to reenter - just enough for the landing burn which is pretty minimal. It's dwarfed by the extra weight required.
8:46 Sadly I don’t own that dvd but I would send it if I did 😂
I subscribed to this channel for interesting calculations, and I think other people did too, so if you do a more detailed analysis with more factors it would be very interesting
On this video I was trying to address a very specific question, but there's going to be something more general coming up.
I did a similar evaluation from different principles. I started with the assumptions of same planetary density (which is reasonable as Mercury and Venus have similar densities, and yet still is a very good case as Earth has the highest density of any planet in the Solar system), and similar atmospheres (ie I could ignore drag losses). From that I got changes in orbital velocities at 400km altitude that nearly exactly align with the change in gravity. 0.9g was just under 90% velocity, 1.1g was just over 110%, and even 2g was just over 200% velocity. I also assumed small changes in gravity losses making the change in required dV closer to 89%, 111%, etcetera.
With a similar Falcon 9 model, that translates to ~13,000kg to 400km on a 1.1g world, and ~30,000kg on a 0.9g world. I also got an SSTO payload for Starship of nearly 20,000kg on a 0.9g world, though that doesn't allow for a propulsive landing, full reuse would still require 2 stages at 0.9g.
It was also interesting that, assuming a commensurate increase in thrust (to avoid horrible gravity losses), expendable Falcon 9 could probably reach orbit on a 1.5g Earth (with ~1.5 the diameter as well). A 2g world is extremely unfavourable for chemical rocketry, requiring somewhere around 19,000 m/s of dV to reach low orbit, and I may have significantly underestimated gravity losses. I think it is possible, but only with very efficient structures and lots of stages.
Thanks. It's always interesting to compare numbers.
Alright, got it. Use three stage rockets for ascents from super earths.
Nice picture. I never thought the Starliner would be so big compared with the earth pizza...
It's a really, really, really big rocket.
Typo: At 0:32 you write "how would increased gravity effect rockets?" "effect" should be "affect".
"Affect" (to influence) is a verb, and "effect" is both a noun (the result of the influence of something else) and a verb (to manifest with intention). Its verb meaning is only rarely used, and it's clearly not what you meant here.
Affect: fool around
Effect: find out
Not with a nuclear thermal rocket.
So more like methalox rocket would be less practical, not reusable rockets in general.
Isn’t the starship( with booster) mass fraction to orbit something like 2 percent. It doesn’t sound like it would take much more gravity to make that zero ?
My estimate is 4 percent.
OP doesn’t know the different between “effect” and “affect”. 😂
Op knows the difference, but contrary to popular opinion, op is not a robot and therefore sometimes make makes mistakes.
A book editor I was writing for once told me "don't let 'perfect' be the enemy of 'good enough'" and I've found that to be sage advice.
Yep, but you all missed the real point: higher gravity, requires the rockets to be more robust, so they weigh more. And to carry more propellant, which makes the rocket even bigger and heavier... Yep, in higher gravity your Earth rockets are collapsing under their own weight and on dynamic forces... because you forget what inertia is...
Scaling linear the weight means you forget that the force is a power of acceleration... Not to say you never calculate the escape velocity, how much energy will require that escape velocity, and the rotation speed influence, to see how fast you need to fly just for equilibrium... So your calculation did not convince me. I am sure you missed a lot...
Completely missing the point. He was talking about full reusability, i.e. Starship/Super Heavy. The factor most sensitive to orbital velocity is reentry heating. 5% more velocity means about 20% more heat, which likely means 20% more heat shield mass. It would also mean 30% more heat shield weight. Now structural integrity is also completely ignored. If your ship is heavier, it needs thicker walls, increasing mass and weight even further. This has a similar runaway effect as the rocket equation has on dV. Finally, I think he was actually talking about planet mass, not surface gravity strength (this is an actual error of course), more massive planets are denser and have a disproportionally higher surface gravity.
I might be missing something but it seems your energy calculation only accounts for the increased orbit velocity but where do you take in account of the fact payload, fuel and all structures weigh 10% more.
I'm basically claiming that all the other costs increase at the same rate as orbital velocity because it's simpler.
I'm gonna make an assumption before watching the video. Elon is exaggerating "impossible", but reference to the Falcon 9 specifically it would be impossible. With larger rockets it wouldn't.
My guess is orbital speeds would be the biggest factor.
Neat to see how super wrong I was. I did see that you missed something, Starship coming in hotter and needing to land with more mass and not just talking about the landing burn, but the actually weight of reinforced joints and landing gear (flaps and thermal insulation) That would more than chip away at that 4% payload.
The factor applies to the whole vehicle and that would include reentry structural requirements since those influence the earth gravity Delta v.
I have no idea how the higher gravity actually influences reentry. The factor could be higher or it could be lower.
Nice work.
Elon did rigorous simulations in Kerbal Space Program.
What about the 10 to 20% gains you coukd acheive from an equatorial launch?
The earth's rotation at the equator is about 465 meters per second, and the rotation at 28 degrees (cape canaveral) is about 400 meters per second, so it's a small difference - less than 1%.
That's assuming you are willing to launch to an orbit at the natural inclination of the site or higher.
If the ultimate orbit you are targeting is geostationary, then launching from 28 degrees costs about 400 meters per second over launching from 0 degrees as you need to do an inclination change to get to 0 degrees.
Thanks for thinking that out. However you proofed Elon wrong here and pointed out the problem with Starship. The problem with Starship (just in my opinion) is that the are effected by the reentry heat is too large which adds "kind of" unnecessary mass to it. So I'd suggest that a design with less area exposed to reentry heat would be easier. In other words I favor a landing capsule design --- maybe like Stoke space etc. The heast shield for the next test fligiht is going to be heavier I'd say SpaceX official defined the heat shield as purely experimental.
Less area for a given mass may mean higher re-entry heating.
I have a video where I talk about stoke. It's not clear if their design works at all, and starship is ultimately designed for Mars.
@@EagerSpace I think the basic idea behind the landing capsule design was less area exposed and the hot air escaping in a way the upper part doesn't get hit by the hot gas. I suppose it is a kind of simple concept because it is used so much for reentry. Probably some kind of automatic flight stabilization too. Reminds me on some kind of roly-poly or wobble doll.
Basically because with 10% higher gravity two stage rockets become useless
Falcon 9 works fine. It's not great, but it works fine.
@@EagerSpace yeah, with only orbital velocity at not orbital hight. 400km orbit would be inside the earth with 10% more gravity
It could be a denser earth rather than a bigger one.
"drag loss is small"
Well, there goes realism
The "Qoute" from Elon could have been from me ;-)
Of corse I sayconfirmed!
I always said: "Rockets have so little payload and need so much propellant, that it would be
impossible to make rockets that have any payload to orbitals, if the Earth would have some significant higher acceleration of gravity.
It is not very importand where the threshold is, at 5% 10% or 15% but its obvious for me that this around 10% by simple reasoning. If you need around 90% of the weightt of the rocket for propellant, then it is a good first guess, that you need around 100% propellant at 10% higher gravity force. So this a simple and not correct calculation, but good enough for a estimation.
With diffferent technology like maglev-ramp it might be possible at double earth gravity,
but not with chemical based rockets as used nowadays.
When Elon says impossible at 110% gravity he means full reusability at scale (starship) is impossible for MARS. At that gravity, it would take 100s of tanker flights to refill one starship for MARS. Now answer is it super easy at 90%.
Probably not impossible but not economically feasible. Starship was after all optimized for earth gravity and a compromize between cost and performance. With enough money it could be made out of carbon fibre and use hydrogen to reduce weight and increase isp - but stainless steel and methane are able to get the job done cheaper and the performance is "good enough"
I'm very interested in seeing what Neutron will be like because Rocket Lab is the master of carbon fiber. I think the performance is going to surprise a lot of people.
I think carbon would have been a disaster for starship. Starship is really easy to change because you can quickly modify a stainless steel design, but carbon fiber requires new molds and that's a ton of work. There's also the transportation aspect - Starship is hard enough with the factory just down the road from the launch site, and their original plan was to build starships in LA and then ship them to Boca Chica. No way would that work.
I'm not excited about hydrogen for reusable rockets; the second-stage tanks are so much bigger so you are adding a lot of dry weight to the system.
The advantages of hydrogen quickly disappear when the entire ship needs to be returned, huge tanks would increase the diameter of an already thick ship, along with its mass, which cannot be discarded, carbon fibre not good for cryogenic fuel and not good for re-entry and reuse
Yes. It's also *really* hard to build high thrust hydrogen engines.
are you considering that a planet with higher gravity tends to also have bigger radius so you would need even more delta-v?
applying straight multipliers to a composite delta-v is really lazy and likely faulty.
Yes and yes. But the answer is directionally correct she is good enough to understand why full reuse is such a pain.
I could've sworn when watching Musk's gaming stream that he said it was 20% higher Earth gravity that he said was impossible. But maybe I misremembered while watching him play DIablo IV with a bunch of teenagers.
If he did, then my numbers align more closely with his.
Maybe once they get most everything working they can build some parts out of lighter materials.
The rocket itself is only 6% of the total weight. 90% is fuel, 4% is payload.
There is no way this calculation is correct.
If you add 10% more gravity, then that is comparable to adding 10% of the fully fueled rocket as payload when on the launch pad.
Not just 10% more payload.
No, that's not how the rocket equation works. Your mass at stage shutdown is unchanged.
In terms of the required liftoff thrust, you are correct that it would be equivalent to adding 10% extra mass, but what happens after liftoff follows the rocket equation.
Yes i was thinking this too. You would need extra rocket engines to lift off adding way more mass along with a stronger frame to deal with the extra thrust. F9 produces 7.6MN of thrust and at lauch gravity pulles with 5.7MN giving a positive thrust of 1.9MN with one G. If everything now weights 10% more gravity will pull with 6.3MN leaving only 1.3MN of thrust a 32% loss. This effect componds gravity losses as you are accelerating a lot slower now.
From 3% to 9% of the total mass, three times, that's a lot.
Why so few viewers on this site. Better than most of the bot voiced, repetitive daily churn
Considering how much Elon knows and how smart he is, he may get some things wrong.
The sarcasm is strong with this one! (Yoda)
Is claim about version 2 , starship I think is wrong, it is only slightly bigger, but to carry 100 tonne of to orbit, starship needs to be twice it's current size . How much exactly ? So currently fully stacked starship weight 5000t , and most likely can carry 50 t to orbit . 50×100/5000 = 1% , only 1% of it's mass is carried to space . So to have 100t , there need to be 10000×1%/100 = 100t . This starship needs to be 10000 tonne heavier to actually achieve those numbers. Version 3 of starship I'm not sure how large it needs to be since the trust has increased.
This is completely wrong. The percentage will change with the size of the vehicle. Bigger vehicles are generally more mass efficient. Twice the size might give four times the payload, or more, or less. It depends on the specifics.
Regarding Starship, the changes between versions are not just to make the vehicle larger. There are also changes like integrating the hotstage ring, removing heat shielding on the engines (as the engines will be more robust), increasing thrust-to-weight on the engines, shaving off excess weight all over the place, etc.
The current version of Starship is very unoptimized. SpaceX will focus on optimization for the next few versions, once they have a minimum viable product.
@@SpaceAdvocate they did say the trust would increase, so I guess there would be some improvement although I don't know how much . How does increasing size increase efficiency?
@@m.c.4674 One basic thing that increases mass efficiency is that most of the mass is in the surface of the vehicle. This means that the mass of the vehicle is strongly correlated to the surface area of the vehicle, rather than the volume.
As an example, the formula for the circumference of a circle is 2 * pi * r, while the formula for the area is pi * r ^2. As you increase the radius of the circle, the area increases much faster than the circumference. This is the same for the volume of a cylinder, as well as many other shapes. The volume increases faster than the surface area, as you increase the size.
As an example, if you have a 9 meter diameter, 20 meter tall cylinder, and double it to 40 meters, the volume goes from 1272 cubic meters to 2544 cubic meters, or an increase of 100%. While the surface area goes from 692 square meters to 1257 square meters, or an increase of 82%.
Other things that increase efficiency for larger vehicles is that some components don't need to be any bigger for a larger vehicle. Like the avionics. You can often use the exact same avionics for a larger vehicle than for a smaller vehicle. There are many components like this, which do not need to be any bigger for a larger vehicle.
One big example for Starship specifically is that it's unlikely that the future version will have a bigger payload fairing. The current payload fairing is plenty big, and can accommodate a 100-200 ton payload. This is like 40% of the length of the Starship upper stage which doesn't have to change at all.
@@SpaceAdvocate but it is increasing in length , even if it wasn't drag also increases with diameter , about the same as volume.
Computer , sensor in a ship this big is already microscopic compared to the ship . And structural support will need to increase as the mass increases.
I'm a space x fan , I just want actual proven numbers on the payload that starship new raptor engine can lift to space . 10% more thrust , could be 10% faster fuel intake, or preferably a 10% increase in the speed the gas is being released (I think they call it bar pressure, something like that). Let's say it is 10% more bar pressure, okay so per tonne of fuel 10% isn't used , the rocket is pretty much entirely fuel , so 4500 tonne of fuel , so then the ship will have a remaining 450 tonne of fuel. If 4500 tonne of fuel can only life 1% of payload to space and 450 tonne of fuel is 10 times less , then that 10% increase in bar pressure would total to 1.1 % of mass being payload. So a payload increase of 5 tonne totaling 55 tonne , version 2 I think is about 10 percent longer so that another 5 tonne, so total tonnage of version 2 would be by my approximate 60 tonne.
Version 3 is still completely hypothetical, they may never achieve this , or even want to do this , 33 engines and not one ever blowing up, yeah see you in 100 years .those engine shields will remain.
I'm am biased in that I don't think starship should do any mission outside low earth orbit. I don't think any of the current rocket engine cryogenic fuel or not is efficient enough to sustainably go to Mars , moon etc..
Ion thrusters are simply better , rockets release gas molecules in slow motion in comparison to ion thrusters. Starship has the payload capacity to low earth orbit to build a true starship, one power by ion thrusters.
@@SpaceAdvocate when it is low gravity or space , using rockets is kinda not good at all .
Ion thrusters typically have specific impulses in the range of 2,000 to 5,000 seconds. This is much higher than the specific impulse of chemical rockets, which are typically in the range of 200 to 400 seconds
Also, what do you think about the Elon's mention of our having a thick atmosphere as a contributing factor to full reusability being very difficult on Earth? It's interesting in light of you considering drag during ascent to be so negligible that you didn't include it in your model in this video. In your estimation, would full reusability be easier if we had a thinner atmosphere?
Atmosphere is interesting (and I think very complicated) because, for a reusable vehicle, it doesn't just impact drag on ascent, it also affects various aspects of reentry: how much energy can you bleed off via drag/friction heat, how fast will this happen, how hot will things get, what trajectory do you need to use, what terminal velocity will you arrive at, and so on.
And so, depending on what sorts of changes you made to the atmosphere, it seems it could potentially have quite a substantial impact on the TPS design and its mass (or even the extent to which a TPS, mostly-alone, is actually capable of bleeding off the vast majority of your energy during return; and, therefore, whether perhaps you'd need to lean more on rocket retropropulsion etc), which could have big implications for the launch vehicle dry mass and the overall vehicle design (which comes back and affects ascent too).
At least for cases with a *substantially* thinner atmosphere, my impression is that ascent would be a little bit easier, but then those gains would be small in comparison to the problem on return of "how the hell am I going to get rid of all of this energy?!"
Mars landings are very difficult due to its thin atmosphere: just to land a 1-ton rover, you end up needing very elaborate multi-step techniques involving e.g. an ablative heat shield, followed by a GIGANTIC supersonic parachute, ultimately followed by quite a bit of expensive powered descent. (And granted, the Mars examples we have all involve coming in at interplanetary-rather than merely orbital-velocity; and they're also pretty mass-limited overall for what measures they can reasonably employ for entry, due to not being a giant, orbitally-refueled vehicle; but still, the thin atmosphere makes EDL a substantial pain, I believe mainly because it simply limits how much energy you can get rid of passively via drag techniques.)
Interesting question. Thinner atmosphere changes the reentry heating profile and I'm not sure how.
Elon might have been exaggerating, but wow.
Love this channel!!
Thank you!
Interesting results, I found them counterintuitive.
I'm confused. I thought the Starship was more efficient for fuel to payload. What's the point, then?
@@TimJSwan The point of Starship is that it's fully reusable, and also a capable Mars transport vehicle? I don't know that I understand the question.
@@TimJSwan Cheap propellant is cheap. If they can fly Starship for even $10MM of props and get Booster and Ship back, that likely costs less than expending a F9 upper stage. It should cost much less, to orbit 8x the payload.
@@TimJSwan No - it uses way more fuel. It's based on the fact that fuel is cheaper than rockets, and that by throwing more of the former at the problem, you can brute force the rocket equation.
What was the point of this video?
Full reusablity is about cost and has almost nothing to do with the efficiency of lifting a load from a gravity well.
If there is a model where chucking out the first and/or 2nd stage were financially profitable I am sure it would have been considered by NASA a long time ago.
There is also the question of return trip and ferrying loads to and from destination orbits even if you set aside landing and relaunching of a space vehicle.
I don't know what test you're referring to. I'm just here for entertainment purposes. 😊
Pop quiz today. Put your books under your desk and I'll hand them out. You have 15 minutes.
Gravity doesn't exist we live under a system called density where things get pushed down from the top not pulled down from the bottom sry
Uh...
If Earth's gravity is +10%, then orbital velocity at 400km will be faster. More delta-v will be needed.
I do not see that variable in your calculation.
My gut feel is that Elon is right.
The velocity equation is the orbital velocity.
@@EagerSpacegravity is in your equation as a force to be resisted.
I didn't see where orbital velocity at 400 km altitude changes with gravity changing.
Perhaps I am misunderstanding?
The orbital velocity is sqrt((gravitation constant * mass of the earth ) / orbital distance from the center of the earth).
You would get higher gravity because the mass of the earth was greater - either you have a bigger earth or the earth is more dense. I chose the "more dense" option as it was simpler.
@@EagerSpace got it. Thanks!
No worries. What that term meant wasn't as clear as I hoped.