Will Starship Get Bigger ? Propellant tank sizes and rocket diameters
HTML-код
- Опубликовано: 8 июл 2024
- There has been talk of bigger starships in the longer term. Why would SpaceX want to do that, and how would the choose a size for their bigger rocket?
00:00 Intro
00:35 What makes an efficient propellant tank?
02:07 Figuring out the propellant tank volume for a rocket
04:59 How big does a Falcon 9 first stage want to be?
06:04 The Falcon 9 second stage the perfect size...
07:41 Tanks sizes for the ULA Vulcan...
08:30 Why is the Saturn V first stage so small?
09:47 Finally some content on Starship
10:42 Does physics prefer larger rockets?
12:03 The graph that answers our main question.
13:37 Is tank pressure an issue?
15:16 Why bigger rockets would be a major pain
16:09 What kind of plane is starship?
16:45 Final thoughts
@Eager_Space on Twitter
Triabolical_ on Reddit
/ eagernetwork
/ eager-space-1038430522... 
Наука
Eager Space been cooking this week
Cooking with liquid gas!
@@PetesGuideuhhh
Maybe meth...
@@rexmann1984 ...ane
Yessir
I don't think we'll see bigger diameter Starships until at the earliest 2030. There's still a ton of work for the 9m starship to do, and it's already comedically oversized for the vast majority of payloads.
Great analysis as always!
That's what I don't really understand why Blue Origin or ULA are going for bigger fairings. The largest satellite ever sent into orbit was with a regular Falcon 9 fairing. The issue isn't size, it's cost. And they're going backwards from there.
Starship I completely understand the fairing size. They're their own customer. Starlink V2 (and possibly V3 satellites. Something Musk briefly mentioned during the Everyday Astronaut tour) are massive and heavy. So they need the extra size for them. But for the rest, I don't really think a bigger fairing is all that important tbh
@snakevenom4954 makes engineering a payload a lot simpler, and often cheaper, when you reduce the mass/volume constraints.
@@snakevenom4954 I will re-review the video again, but I thought the discourse there indicated that Vulcan Centaur had a decent diameter, given the fuels and materials used, at 5.4 meters?
@@michaeldunne338 Hydrogen preferred a smaller diameter but they kept the same diameter for a little less performance
@@citizenblue I agree. But if the largest satellite fit into a Falcon 9 fairing, how many satellites will need a larger fairing? I'm sure some will. But enough to be a market? Not likely
This plan is very similar to how they developed Falcon 9, it took them several years and iterations before they got to the Block V booster.
Dunno, the increase in diameter and height dictates a completely new structure rather than just putting a plug in an existing structure to make it longer, metal structures being a bit less limited to the moulding needed to make a composite structure like falcon.
Falcon 9 just grew in length.
Growing in diameter is a completely different matter. And Starship / Super Heavy won't change the diameter either, as far too many very expensive things have to change.
Entering my 3rd year as an Aerospace Engineering student and I’ve got to say, I love your videos. These videos are incredibly informative and well thought out. They cleared up some confusions I’ve had and gave me a new perspective of spacecraft elements. Thanks ES
Something else to consider with Starship is the reentry cross section. A shorter but wider Starship will have a different belly cross section than a tall and thin Starship. Although a larger cross section means means more surface area that needs tiles, it also means a gentler reentry. That too has some optimization equation, but it's probably more complicated due to heating limits and such.
*No need for tiles at all. just drill lots of micro holes. then pump out dry ice out of those holes to form a cold co2 insulating boundary layer. you dont even really need a pump. the heat of re-entry will cause melting of the dry ice and high pressure dry ice co2 to come out of the micro holes to form the insulating boundary layer.*
@@esecallumwhat lmao
@@furriesinouterspaceUnited learn to read and listen
@@esecallum Uh you spatted some absolute nonsense, none of that will work.
@@furriesinouterspaceUnited i proved it it lab with bunsen burner-e and an air compressor. you are regurgitaing it cant be done
Nice video! Quick addition: the mean height of a rocket is also limited by its thrust density. One of the reasons to taper a rocket like the Saturn V is to fit more engines underneath while still getting sensible aspect ratios in the tanks above it. Starship gets to have as high an aspect ratio as it does in significant part because of how unusually powerful its engines are and how packed its flamey end is with them.
Yes, this is an often overlooked factor.
Short rockets don't need to pack the engines in very tightly. Electron has lots of space between engine bells, and the bells only take up a small percentage of the area. F9 is quite closely packed, and Super heavy is just insane with engines jammed in so tightly that most can't gimbal.
So an 18m Starship full stack isn't going to ever be twice as tall as the 9m. It just physically can't be.
Another reason for the steps in the Saturn V was the design process. The Third stage was a reused Saturn 1 / 1B Second stage & thus was designed first. The First stage was designed second; because without it the Saturn V (originally C4) was not going anywhere. This left the Second stage to be designed last. This gave them all sorts of problems, not only did they have to fit between the other two; but weight overruns were left to them to sort out. The Second stage thus had the most advanced engineering solutions of all stages. Such as the common bulkhead between the hydrogen Lox tanks.
9:34 Please get carried away like this more often.
You forgot to talk about the heat shield! The heat shield area increases in a linear fashion to an increase in diameter. Also, a starship of greater diameter may actually slow down more quickly in the atmosphere because there’s a greater area for the atmosphere to work on. so, increasing the diameter of the starship may not only increase the amount of propellant that can be carried, but also have some real increases in the effectiveness and efficiency of the heat shield. Since the heat is getting heavier at this point because of the addition of the ablative layer, Looking for ways that the heat shield will become a smaller fraction of a total weight of the upper stage could be a real advantage.
Definitely true.
I was going to do that originally but I thought there was already too many graphs and too much mass.
@@EagerSpace
Nonetheless, a nice video. I wonder what you think of the booster catch attempt for flight five? My question is what does the last second abort look like? If SpaceX loses control of the booster (which is never landed completely successfully, even on flight four) Where will the booster crash if it’s already close to the tower? I’m puzzled why they’re rushing this because I don’t see her upside for it, but I do see a lot of downsides.
If you add that question to my "ask me a question" video, I'll probably be able to answer it there in detail.
I personally don't see much downside as long as they think they can avoid dropping it on the propellant tanks. For abort they could probably drop it off in another direction, but we've seen very few issues with running raptors.
@@EagerSpace That, and the fact SpaceX in general has their software in tiptop condition. To date I don't know of any software error ever causing major problems. In sharp contrast to that other aerospace company who's name starts with a B and charges 5 times more.
@@wbwarren57Also the heatshield has to work less because a bigger vehicle create a shockwave that is further away from the vehicle itself, it's the reason why capsules are shaped the way they are on the bottom.
you never miss
Wait for my next video, I think you might change your mind.
I imagine a century from now, starship will be remembered as the Ford Modle T of early space flight.
More like the first deep water sailing ships, like the caravel or the galleon.
Rockets of Unusual Size? I don't think they exist.
Great video!
Thank you for making the airliner class analogy.
I do wonder what challenges SpaceX would face if they had to retool factories for a wider starship
The factory would be easy enough I think, most of the stuff in there i suspect is just jigs and such which would be easy to retool. But the bays would be a pain since they are designed for the current diameter.
Bays? 🤔
Dude this was seriously awesome
I LOVE this channel!
Hell yeah! Can't wait to watch this
your recent videos have blown up in views and you deserve it. Keep up the amazing videos!
Thanks. I have made some changes but I think it started once I got to 5000 subs.
Why not both? 9 meters for payload is absolutely huge relative to anything we’d want to put up in the near future (say… 20 years out?). I could see a scenario in which the 9m starships handle the actual payloads, while the absolutely gigantic 12m starships are just used for refueling. Eventually, the 12m rockets could be phased in for payloads after that.
There is an advantage a bigger rocket gains on reentry too: A bigger radius object pushes the boundary layer further away from itself on reentry, therefore the heating is reduced. So you can get away with a thinner, weaker, and thus lighter heatshield than a smaller diameter vehicle.
Interesting. Do you know if any references I can read?
@@EagerSpace Scott Manley has a great video on it: ruclips.net/video/hLHo9ZM3Bis/видео.html
NASA also published this presentation on reentry thermodynamics, that talks a little about the stagnation point, and how the radius is important, but it discusses a bunch of other stuff too: tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf
Thanks for the paper. Scott does great videos but I don't watch them if its a topic I might want to cover - which is most of his videos - because I don't want to be derivative.
Thanks for this video
MOAR Eager Space! Yesss!! 😊
Glad to see those chapters in the description + increased video posting cadance + Hot sauce Topics 😉
Fantastic video. I was thinking you would not talk about pressure, but you did. The math is simple and enough for people to start thinking instead of just talking.
Ok, you concluded the most important factor is choosing rocket diameter based the amount of propellant you want. There is a strong reason to go bigger NOW not in 10-20 years. They want to bring as much propellants as possible in the tanker ships, to reduce the amount of tanker flights they need to refill for Mars and Moon trajectories. I think they should build 12m tankers, to refill 9m cargo and crew Starships. Some are claiming the imagined 9m version of a tanker would take 12-17 flights. If is that bad, they might want to go to 12m tankers asap. (for efficiency rather than to shut up the skeptics).
I don't think number of tanker flights is something they care about directly.
They do care about how much refueling will cost and they care about the hassle of supporting tanker flights if the numbers per refueling get big enough to be operationally problematic, but you are saying that they should throw - let's pick a number - a few billion dollars towards a 12 meter variant just to reduce the number of tanker flights.
It's not clear that at 12 meter new version is a win from a cost perspective.
Another banger video, sir
Banger video
The assumption that the tank is the same thickness is simply wrong. If the tank is twice the diameter, and designed to hold to the same pressure, then the walls need to be twice as thick. Also, rockets have height limits if all the engines ar on the bottom. There's a limit to how many engines you can bit under each stage. So it's impractical to build cylindrical rockets much bigger than starship. This is why the N1 was conical despite being even smaller than starship.
He talks about this at 13:50
The N1 was conical mostly because they were using spherical propellant tanks. That's the ratio between Lox & Kerosene.
Is the pressure driving the thickness or is it the structural load?
@chrissouthgate4554 Fair point. A better example would be the flared bottom of the Saturn V, to account for the massive F1 engines. No matter how you slice it, you will reach a point where there isn't enough space on the bottom of the rocket to leverage enough thrust to get the rocket off the ground.
A single raptor engine can only lift the weight of a column of water with its own footprint 200m tall. Since you can't fill 100% of the area under the rocket with engines and you need a thrust to weight ratio of at least 1.5:1 to efficiently reach orbit, the 150m tall starship V3 will be pushing the limits of how tall a vehicle can be and still fly.
@EagerSpace The rocket derives its rigidity from the internal pressure. The taller the rocket, the higher the necessary pressure to maintain rigidity. Basically, you want the walls to always be under tensile load and never have a significant compressive load.
Glad i found this channel
It's great. No fluff. Just dives right in to the good stuff.
Terran Space Academy is also great for the same reasons.
@@citizenblue love channels that do that
I would have mentioned the issue with thrust density with regard to height. Unless SpaceX comes up with continually better engines, Starship can get wider, but it can’t get taller. You no longer have room for enough engines at the bottom.
150 meters is pretty much the max you can get to with current engine technology (Raptor V3). (Assuming same diameter for the whole rocket.)
BTW, this means that if you don’t have really good engines, you are limited to a lower height. It is an important design constraint. As long as New Glenn uses the ORSC BE-4 engine, you’re probably not going to see a version reach much beyond 100 meters, as an example. This could push designers to increase from a 7 meter diameter to 9 or 12 meters, or beyond. If the need arises for a larger more capable rocket.
Agreed. I think a larger diameter will come as soon as they start generating revenue from operations (Starlink, etc...?). Starship is mostly a fuel tanker and the demand for payload is limitless. It's a KC135 refueling an A380.
Eager Space is the Excel version of Perun with powerpoint.
Absolutely outstanding stuff
Great
I wonder if the ship necessarily needs to be the same size as the booster since they use hot staging now.
10:43 nice Princess Bride reference!
It originally said something like "large rockets", and I am so pleased I came up with "rockets of unusual size"
@@EagerSpace You even managed to keep the same acronym! R.O.U.S.
Imagine there will be alotta variations for different purposes.
Would personnel love my own mini version for personal trips to distant moons.
There are some difficulties with rockets over 10 meters in diameter, having to do with airflow over the frontal surface area. Lengthening the rocket is much more efficient than increasing the diameter.
I never heard of your RUclips channel but it popped up in my suggestions.
I must say, you do an excellent job. Thank you.
One tthing you didn't mention was he increase in the number of rocket engines goes up as diameter increases. Maybe the mass and thrust balances out, but it would be nice to hear you say so.
Thanks.
You do get more engines because the area for engines increases with the square of the radius.
As you increase the diameter, the area and mass both (approximately) increase with the square of the radius, so it balances out.
You can’t increase the height, though. That increases mass to the area for engines.
There is not that much advantage from increasing the width as height of the rocket is limited by the thrust by surface of the engines. Next rocket is more likely to be 27 meter wide or something, unless some breakthrough with rocket engines appears or we get some super materials like carbon nanotubes, metallic glass or hot temperature superconductors. Also, the 27 meter wide rocket is likely to be the biggest conventional rocket, as by that time we should have large moon and asteroid resource mining and manufacturing, so biggest Earth exports are likely to be complex things like computer chips and humans.
Asteroid mining would be better done from a base on Mars, lower gravity and much closer to the asteroid belt. Then refine the raw materials on mars and only transport highly refined materials back to earth.
@@schrodingerscat1863 I know it's hard to believe, but asteroid mining is not a thing economically. You can't mine resources from moon, mars or asteroid belt and make it cheaper than what you get on Earth, the math just does not check out. Asteroid mining will basically be exclusive to only space related activities, like making space habitats, spaceships and other space related stuff. Unless price of earth materials drastically raises, like by orders of magnitude, and we figure out good mass drivers, it's not going to happen. This is why I specifically said that Earth made rockets will have to compete with Space made rockets, as for the same reason why it's expensive to send stuff back to earth, it's expensive to send stuff out of earth, so we probably will not be delivering THAT much cargo to orbit with gigantic rockets, we are more likely to just deliver humans and chips, and then spaceships and fuel for spaceships will be made in space.
@@Ormusn2o May not currently be a thing but that will change as technology makes such a venture economically viable. May be 100 years away but it will happen, the resources available in the asteroid belt are vast.
Excellent work. It should be noted that the maximum height of a rocket is set by the thrust per unit area of the base of the rocket. And thrust per unit area of the base will be constant with a given engine type and engine packing density.
How does that determine height? Mass I can see...
@TheEvilmooseofdoom Yeah I wasn't very clear. How about this...
Making a cylindrical rocket wider wont give it any advantage in being able to stack propellant higher.
@@TheEvilmooseofdoom You can’t add height without adding mass. If you’re only increasing the height, you can’t add more engines, and the thrust to weight will drop.
Unless they begin constructing interplanetary ships in space There is a limit to the weight that existing rocket engines can lift into orbit without constantly destroying the launch pad!
Could we get there using the Brisbane tank designs?
This IS a very interesting topic. Another topic I've been curious about is the issue of how many engines is most beneficial. For example, Superheavy can loose an engine or two and still boost Starship enough for it to make orbit. There is a new design with 35 raptors. What is the benefit of more engines? Obviously more thrust, at the cost a little more weight per engine, but that gets the rocket up higher faster, so I assume that cuts into gravity losses? And Starship has an upcoming design revision where it will have nine engines rather than six. And it will hold more fuel. What is the cost of the additional engines and what is the benefit? I imagine there are some interesting graphs to be drawn re. those figures.
You are correct - the faster you burn the fuel, the quicker you can stage. That not only reduces gravity losses but for the first stage, means you are closer to the launch site so it takes a little bit less fuel to get back.
I think for Starship, as a fully reusable rocket, bigger is better.
A bigger Starship can send more stuff with less flights, and since the major increase in the cost of the launch is the propellant (the operations cost I think is more or less independent from the size), you can get a lower $/kg.
Also, you don't need a lot of launches to send a good amount of cargo to LEO, so a super fast turnaround time isn't too obligatory.
Obviously the gains in cargo volume are also there. "Who wants to send a 15 m wide payload into space?" may you ask, the same people that started making 8 m wide modules after Starship became a reality is my answer.
imo a smaller version for cislunar and interplanetary travels combined with a bigger version for tankers and LEO payloads is the best combo. Is not unrealistic to think of an scenario where a 9 meter Starship can be refilled in orbit with just 3 or 4 tankers, instead of ~10.
what also surprises me is that SpaceX never investigated floating starship upright in the ocean and launching that way, much like sea dragon was designed to do.
@@paulmichaelfreedman8334seawater is a bitch on the engines,especially complex ones like the raptors. Zea dragon had super dumb engines that wouldn't get too damaged by the water.
> bigger is better.
Of course this can't be just generally true. 9m width is quite large as-is, and 250 ton payload to LEO (if expendable upper stage) covers all current and near-future needs with lots of room to spare. Why would SpaceX spend large amounts of $$$ and work to redo everything for wider rocket if current one works? It's not like they have nothing to do, it'll take them at least a few years just to get it working reliably a-la F9.
> "Who wants to send a 15 m wide payload into space?" may you ask
For example, what that can be? We currently can't even manufacture 15m diameter monolithic telescope mirrors that large, maxed out at ~8m.
But if necessary, "hammerhead" fairings can accommodate something like that on a narrower rocket.
Anyone aware that there is more than one orbit around the earth? That's the same problem as with large planes, you will have hard time to find enough passengers that want to go to the same place at the same time.
I think there is no need for larger Starship at this moment. It is huge achievement as it is, just get it right at this dimensions, bring errors to minimum and this is the rocket for 21st century.
Is there ever a time when payload width overpowers the need for the most efficient rocket?
SpaceX will take whatever gains they can get at this point. It's not like they can keep leave efficiency on the floor. This entire endeavor rides on the edges of what is physically possible.
Before Musk started talking about orbital fuel depots I had always believed SpaceX would ultimately build a number of Booster/Starships that were twice as wide and twice as tall to facilitate refueling Moon and Mars bound Starships with one launch. Doubling both diameter and height would allow roughly 8 times the payload delivery to LEO compared to the normal size.
Say existing booster has 3400 mT prop and ss has 1200 mT prop, that's 86 m of combined tank wall. Doubling tank diameter and height will require thicker steel, approx additional 27 mT in beefier bulkheads and 255.5 mT in bigger & thicker tank walls (and I'm not adjusting the non-tank masses.) Your dry mass is now at least 115% heavier than before. The net dV requirements aren't changing, but drag losses will be much higher, so prop fraction will be worse. At best you're getting a 3.75x increase in delivered payload for 8x increase in prop. The rocket equation is a stinker. Loading more raptors on the bigger cross-section won't improve the prop fraction and will greatly increase the dry mass.
Regarding raptor mass, 18m diameter shell can fit 3-6 sea level raptors x 1.5mT and ~36 vac raptors x 1.75mT, so the additional 33 vac raptors will add ~58mT to dry mass. I think I jumped from considering the whole system to just booster mass when I said 115% additional. If dry booster = 250 and dry ship = 150, the old dry mass is 400. Add 27 from bulkheads, 255.5 from tank walls, 58 from extra vac raptors gives 85% extra dry mass., which should give 4.3x payload for 8x prop.
As of a day or two ago, the vertical tank farm has been completely cut down and harvested. Do you have access to newer photos? RGV might be willing to share.
Eager Space you any reference material for this topic ?
I can’t believe you didn’t look at neutron as an example, 7 meter diameter first stage and then a 5 meter diameter second stage. Would have been very interesting to see
I don't think there are any published propellant figures for neutron. I could guess based on the sizes they've talked about but they aren't limited to traditional tank sizes.
Make it big enough to fit 2-4 f-22's in it. The rapid strike capabilities of that would be profound.
Another complicating factor is reentry heat load. Smaller vehicles are better suited for reentry because they exhibit faster deceleration and can slow down more at higher altitude.
That’s inaccurate. You want a low mass relative to the aerodynamic cross section. That’s possible to achieve on both smaller and larger vehicles. For crewed vehicles, I would think it’s easier to accomplish on larger vehicles, as the volume needed for the crew is easier to work around.
@SpaceAdvocate Incorrect. The larger the vehicle, the thicker the walls need to be, the greater the mass to cross-sectional area.
Starship is presently a one size fits all design, but Starship has a number of different roles which have different design requirements. Firstly, as a tanker and an orbital refuelling station, the bigger the better resulting in fewer launches and lower boil off of propellant while waiting. As a lunar transfer vehicle, it is much bigger than the Orion capsule so flexibility in terms of cargo and crew number. If it were just to move crew to lunar orbit then bring them back to Earth orbit, then the present starship with further development of the heat shield would probably the way to go. Cargo to the lunar surface initially would be one way with maximum mass to fuel ratio - just enough to land. The vehicle could be reused as habitation and/or construction material. A lunar lander needs to carry less cargo and more fuel to return to orbit. It could be a stripped down standard Starship. A lot depends on in situ fuel production.
For Mars again bigger tankers in orbit, but landers should be more specialise to utilise the thinner atmosphere- perhaps a more elliptical cross section to maximise aerobraking. An interesting decade is guaranteed.
The starship can technically carry enough fuel to not need fuel production on the moon. It can get there from low Earth orbit and back on a full tank.
Without in-situ fuel production on the moon, you will just be more limited in how much material you can bring back.
Why did SpaceX goof so badly with the lack of water suppression for Starship IFT-1? What about their engineering process and the available analysis tools wasn’t up to the significant challenge?
Based on the Data they gathered through all those static fires they believed the concrete would withstand one launch. What probably happended is that the ground underneath the concrete caved in, creating a void beneath the pad and the concrete just gave up. (i believe Musk said that but i couldn't find where and when he said it)
They didn't. They knew an upgrade was required and had the equipment on site ready to be put in but decided based on the tests done to date to risk one flight rather than delay.
Yes, just not width wise for a LONG ass time, it will go in length over time, just as F9 did, reason being is that all the launch infrastructure would need changing to accommodate a wider starship a longer starship is fine though, and we already know a longer startship is coming, but that's V2 I will assuming there will be a V3 and maybe even or 4 and 5 as the engines improve their thrust.
Starship factory is at the launch site. This is an advantage when growing diameter. There is too much advantage to growing diameter. It will eventually happen. There could be a reducer for using prior generation 2nd stage Starships on a booster. I look forward to changes.
It might but at the huge expense of scrapping much of what they just built.
Radius=1/2 x Diameter.
Volume= (PI x Radius x Radius) x Height
Height = 100 meters
Diameter=9 meters. Radius = 4.5 meters
Volume = (3.14*4.5*4.5)*100 = 6,361 cu meters
Height = 150 meters
Volume = (3.14*4.5*4.5)x150 = 9,542 cu meters
Height = 100 meters
Diameter=18 meters. Radius = 9 meters
Volume = (3.14*9*9)*100 = 25,442 cu meters
Height = 150 meters
Volume = (3.14*9*9)x150 = 38,170 cu meters
2x the diameter yields 4x the volume.
The optimum height of a rocket is 10-20x the diameter.
NISTIR 6646 records viscosities for RP-1 down to -30°C, where it could reach a density of 836 kg/m^3
Back when I looked at RP-1 I tried to pick a decent spot for viscosity. You can get it a little colder but you get close to gel, and since RP-1 is a standard rather than a specific mix my guess is that you would want a little margin.
There are also aerodynamic considerations
So, out of curiosity, how would an estimate on internal volume of a 12 meter crewed starship compare to the ISS?
That aside, while I don't disagree that the 9m version is likely to be the standard for some time, I would at the same time be not overly surprised if a 12 meter were to come along down the line as the next step, as it were. It likely would have to wait until after establishment of market demands driven by 9m Starship, but still, it's within the industrial capacity to implement, unlike for gains for 15m+ rockets of sufficient length to be necessary.
As a different aside, how practical / feasible / likely do you think it would be for us to see in the future a space station that is just 4 modified crew starships docked to a single central hub module? And how would it compare to current / historical / likely other private space station programs going on right now?
Can you add those questions to the "ask me a question" video I dropped recently?
since the raptor engines are not operating at full thrust and they don't need to re-light all the engines for landing either stage, it makes sense that you'd use up more of that untapped energy margin
There's a couple of other factors to consider. Firstly fuel boil off during longer duration flights. Intuition says that a larger volume of fuel vs surface area would experience less fuel boil off than splitting the payload into two rockets, thus proportionately less payload would have to be dedicated to managing the temperature of the fuel, with proportionally smaller radiators, etc. The thicker sidewalls of a larger rocket also help shield against the radiation of deep space, at least a little.
And I'm sure the size of the rocket plays a part in reentry flight profiles and heating, although I'm nowhere near smart enough to work out whether a larger vehicle is beneficial or a bigger challenge. Perhaps here the tables are turned and the larger volume to surface area increases the heating as there's more energy to dissipate per unit area...
If Musk is still eyeing a bigger rocket I presume the tradeoffs work out positively.
Is there a possibility that before they go with a larger diameter rocket that SpaceX will go for a Starship Heavy as an interim stage and then flare up the upper stage to 12 meters?
Seeing a rocket with 105 engines take off will be spectacular.
Also going to 18 meters will Raptor be enough or do they need something the size of Rocketdyne F-1?
More raptors seems more likely than bigger ones. Scaling up rarely works linearly. Bigger engines add length too.
Clustering engines has already proven itself and has many advantages. There is no need for larger engines no matter how you scale the rocket.
Just go Mega-Soyuz with four carrot boosters and a potato masher core stage
@@mostevil1082 They haven't yet proven that they can eliminate the 10t+ engine shielding which stops one Raptor RUD cascading into, well, more. Raptor 3 is supposed to solve this problem, I guess by being more reliable and robust? Anyway, if they don't solve the problem, then providing shielding for 33 or 35 engines will continue to be a substantial payload penalty. At some point 5 big engines look easier to shield than 35 small ones. When it comes to human payloads eliminating the shielding gets even harder, NASA is a bit of a stickler that way....
IMHO there's little point going bigger.. what matters is $/kg to LEO.. that requires not only reusability, but also high volume production of the ships, boosters and engines. Make the ships too big and you don't need so many and that eats into the benefit of high volume production. One thing they could do is place a 12 or 15meter diameter payload bay on top of the 9m vehicle for taking occasional bulky payloads but clearly not heavier. (my background is electronics.. cost of which is extremely volume dependant)
How does aerodynamic drag play into tank diameters? Wouldn't you always want to stay a little on the skinny side to keep aero drag lower? Or is it a small component of the overall performance?
Drag is a small part of the energy to get to orbit. Only about 1% iirc
@@EagerSpace Yeah thats very low! Gravity is a cruel mistress.
Something you neglected to mention that might be a significant consideration: wouldn't air resistance increase very significantly with gains in width?
Air resistance is not a big energy loss when launching to orbit. Rockets are slow in the lower atmosphere and do most of their work in vacuum.
If we think only in term of payload actually a falcon 9 is like an 737, falcon heavy like an 777x starship is bigger than A380 x)
BUT starship will be the first fully reusable rocket so it is incomparable right now we can't really compare to the industry we will wait and see in the future when the starship will no longer the only one fully reusable.
SpaceX will not care if a company pay for a starship launch with an almost empty bay unless we have more competitive price in the industry.
I'm not sure what falcon 9 is. Probably the 707 since it's over of the first of it's kind
What about drag?
Drag is generally not a big factor because rockets don't move very quickly in the lower atmosphere.
*No need for tiles at all. just drill lots of micro holes. then pump out dry ice out of those holes to form a cold co2 insulating boundary layer. you dont even really need a pump. the heat of re-entry will cause melting of the dry ice and high pressure dry ice co2 to come out of the micro holes to form the insulating boundary layer.*
The big flaw in that is the mass of all that dry ice and a place to store it.
I personally would like to see 32 meter diameter, or about the side of the Seattle space needle. This size would be most comparable to a submarines
Honestlly there must be a practical limit when the advantages of reusability face the lack of misions and the problems of catching a even bigger starship and booster. So i wouldn't expect starship to get much bigger than maybe 14m. Maybe at some poin a fully disposable bigger vesion might be made for things like sending up a gravity drum of a bigger weeb.
Thickness of a steel tank will double if diameter doubles. That’s because the tension on each ring doubles. Tension per vertical inch = propellent pressure times diameter divided by 2. Propellent pressure depends on acceleration and how far below the top of the propellant
Is propellant pressure driving the thickness or is the structural load driving it?
@@EagerSpace good question. SpaceX standardized on a certain thickness. Ideally I would think the lower rings would be thicker being so many feet below the top of the propellent and having all that propellent accelerated at 3? G makes the tension 3 times greater. Vertical compression on the steel shell may dictate the max height and starship weight on top. That would be another calculation and I believe they must have made both the calculations when figuring out the steel thickness.
There is an error in the reasoning.
The thickness can't be assumed to be the same. It has to become thicker for the larger diameter tank (all other things being equal, such as the maximum pressure difference it can withstand).
I talk about that in the video. The question is whether the skin size is driven by the needs of it as a pressure vessel or the loads that it carries as the main structural member of the rocket holding either the you're stage or the payload.
Oh, that picture of the fast food chicken fried burger was totally unfair at just barely 2 minutes into your video
14:52 "The acceleration due to gravity goes up during the flight of the stage." Surely the acceleration due to gravity remains fairly constant at low altitudes and can only decrease as you get farther from the Earth? Would the correct wording be, "The acceleration of the rocket goes up during flight because the rocket constantly loses mass. (F = ma ⇒ a = F/m) This will increase the pressure on the tank."
Edit: Looking at the equation right now, and I'm not sure how my explanation would work...
Yes, your explanation is correct; it's about the effective gravity not the actual gravity.
@@EagerSpace Ahh, "effective acceleration", there we go
You also didn't mention that a tall skinny rocket experiences less aerodynamic drag than a short fat rocket would. The optimal shape for a tank is spherical but that's a dreadfully inefficient use of space in a rocket.
Space-X will most likely stick with the 9m diameter for quite a while, but to set up a colony on Mars would take 'too many' small 9m rockets at that point they'll jump to a larger diameter. To make the chance worth while they'll need to make it a big chance, 12m isn't worth the infrastructure change so it'll be at least 15m, probably 18m.
Because rockets are slow at launch and spend most of their launch outside that atmosphere, drag losses are a small component of the energy to get into orbit.
We need a big cyber truck!
If the starship lets SpaceX temporarily occupy the position of first shovel factory at the gold rush, you can bet they'll pour R&D money on both the 9 meter and the 12 meter diameters in an effort to stay ahead of a lot of hard working competition. For spaceX, I think that means we'll see at least prototypes.
That's why I brought up the A380.
@@EagerSpace I think a few competitors may try to overtake SpaceX by directly developing a 12 meter starship, especially national agencies like China, Russia, India, Japan, or the EU. All of the major launch providers are seeing a dramatic loss of launch service sales from non-partners to the rising falcon 9 launch cadence, so we may yet see a proper space race once the initial colonization efforts begin.
Nobody outside has even developed a competitor to the Falcon 9 yet.
China is a wildcard; they would like to sell more rockets to the west but there are reasons why they don't see a ton of business. Would be helpful for their lunar aspirations.
Russia barely has a space program left, despite their big plans. Pretty much zero chance of anything new there. They have no sales to take away.
Japan and the EU are firmly on their own paths. I could maybe see Japan doing that but their current plans are pretty fixed and they look to collaborate. Not a lot of commercial sales there. The EU has seriously messed things up with their handling of Ariane 6, but right now they are trying to recover from that and get back to flying their own payloads. They may have ceded most of the GTO market to spacex but with starlink it's not clear what the GTO market is longer term. The EU has falcon 9-ish reusable plans but I'd be surprised to see anything in this decade.
India is also a wildcard; they have been going gangbusters on their program and I think there's a lot of national pride there. My guess is they will end up with an astronaut program first.
Yo
Take 2 boosters 9 meter diameter each side by side and one starship on top with 9*1.41 meter diameter or 12.6 meters. Then eliminate the need for the displacement ring by firing 2 starship raptors that are not covered by the boosters during separation. Or take 3 boosters bundled together with one super sized starship on top. If the boosters are already available, then why not bundle them for bigger payloads?
A sphere has the minimum surface area per volume and it gets better with bigger size. So if you really want to build a huge rocket you gotta ask yourself if air resistance will be much of a concern as you will beat it with sheer volume, mass inertia etc. The Sea Dragon introduced launch emerged in water but I guess it was still too small with around 20 000 t for being practical with a more spherical form. Not done the math but if you go for let's suppose 100 000 t --- you can go for single stage to orbit and water launch and landing. I even thought of hot water/steam as a cheap launch assist as hot water would make a damn cheap fuel/ monopropellant ((poor specific impulse but that doesn't matter for a launch assist)). 500 m/s or maybe 600 m/s exhaust velocity for the steam and shutting down at around 30 or maybe 35km ((dark sky)).
Unfortunately you need to carry the structural loads through the size of the tanks and my guess is that a cylinder is way better at that.
@@EagerSpace .... a cylinder with the minimal surface area --- I suppose the basic idea was just surface to volume ratio gets better with larger volumes.
Yes.
WOW. Mind blown with the what is starship comparison to CRJ, 737/320, and 380. Absolutely nailed that question
Nice work, busy busy I see.
One thing you didn’t mention is thrust density. It is easier to stuff more engines under a bigger diameter rocket, and they are already struggling to meet their thrust goals for the new Starship versions - which you nicely summarized in your video covering the importance of Raptor. At some point they won’t be able to squeeze more performance out of Raptor (safely or reliably), at which point an increase in diameter is required for any further increase in thrust (=payload).
>90% of Starship launches are fuel tankers, so the real analogy is the KC-135. For Elons Mars program, >99% of launches from earth are fuel trips to fill cargo Starships bound for Mars. Starship is almost entirely a fuel tanker, and there is no limit to the need for more payload. If Musk is really serious about Mars, and I believe he is, then an increase in diameter is inevitable, at least as soon as they start generating some revenue via Starlink (presumably?). It will be interesting to see where the revenue comes from to support the Mars program……???
Currently SpaceX is targeting superheavys with 35 engines instead of 33 while maintaining the same diameter, there are already unofficial designs showing that it is possible, so they still have room to improve the current design
And starlink currently has profits of the order of 6 billion dollars
@@APMI-OFICIAL Yeah, but if they are increasing they chamber thrust they should be able to increase the diameter at sea level, so they're probably leaving some sea level performance on the table. It's pretty early in the program to have run out of ability to stretch it any further.
@@marksinclair701 They will max out the raptor and that will likely end development of starship. Another larger version might be built later but likely not for a decade or more.
Which starship is easier to reenter the earth 9 meters or 18?
The bigger the rocket the cheaper the launch cost per 1 kg. This was the main idea for the Sea Dragon rocket
IF you use all the capacity. It can make the price per kilo a bit misleading from a customer perspective but it's a good meter stick for rockets in general.
Sea Dragon never got off the drawing board.
5:35 “Falcon 9 diameter is limited by the roads”
So fly it. Not in an aircraft, it can fly itself. With just an aerodynamic fairing, effectively no cargo mass, it ought to manage a few thousand kms. Point to point in 20-25 minutes.
It wasn't clear whether that would work when they were designing the rocket and it would take a *lot* of work to allow F9 first stage flight over populated areas.
One minor nitpick: at 3:36, you say the density of liquid oxygen is 1141 kg/m3. However, falcon 9 uses supercooled propellants, so the density is actually a bit higher
🤓
Um... Not 30 seconds later I talk about subchilling...
@@EagerSpace 😶
It seems to me, that it would be more practical to build the Starship, in an 18-meter stage, on the moon and launch from there without all the regulations and having to use a booster to defeat the Earth's atmosphere and gravity. You wouldn't need a booster, or as much fuel so you could have more explorers to send to Mars.
Is it possible for you to share your spreadsheet?
People ask me that, and in general the answer is "no". My models are generally pretty messy and unless you understand how they really work you can get wonky results, and you need to know what "wonky" means.
And they generally aren't very complex.
I personally think Elon will move to a larger diameter to support more engines and an actively cooled metallic tps once its determined the tiles cant protect ship enough for rapid reuse.
Maybe in 10 or 15 years, but to do so now means scrapping a lot of building and starting over.
1:37 as a layperson, this seems to be a pretty big assumption to make. It would have been nice if you'd added two or three sentences to justify its validity. For example, what are the typical pressures in those tanks? What are the structural loads?
nevermind, should've watched the whole video first :'D
I did handwave a lot in the section on pressure and structural analysis but I think it's a very complex topic.
@@EagerSpace that section is pretty good and more than I expected. I simply wrote my comment before watching that far.
No worries.
Great presentation. One thing to note is that while pressure vessels would keep a constant mass ratio, things like heat shielding or insulation benefit massively from the square cube law. This would indicate that there is a break-even point for hydrolox where the performance outweighs the added insulation and handling issues (see extreme 1960's fully reusable ssto proposals). speaking of which, why aren't there huge expander cycle engines using multiple chambers (like the russian engines do) to overcome the power/ surface area limitation?
The pumps in the expander cycle discharge at 1.5x to 2x the chamber pressure. The tubes in the thrust chamber and nozzle walls have to hold at least this pressure so that makes them heavier, thus increasing the regenerative surface area increases the weight more than in other types of engines. The extra weight claws back some of the higher performance of the expander cycle.
Fabrication is also quite involved, specially shaped tubes and silver alloy filler are manually fitted and pieced together, then it's fused together in an oven. Not every defect can be repaired, which can scrap the whole chamber. Needing multiple chambers for each engine would make them even more expensive
Make it much taller and we’ve got a flying Washington monument.
14:07 might wanna add captions or diagrams my dude. "15 to 60 PSI" sound really similar along a sixty/sixteen soundalike. Maybe saying "one-five to six-zero PSI" would be more recognisable.
Yes, it would have been nice if that whole slide was clearer.
Ah the cylinder equation… natures cheat code.
They’re not going to increase the diameter on starship. It can only get taller, not wider.
If they make it wider then it’s basically another rocket all together and can’t be called starship. They would need to replace all the GSE, new towers, factories everything so a larger diameter won’t happen till maybe the 2040s/2050s
ROUS get a better delta V if launched from fire swamps.
Thanks for a great video. However... after watching it I get the feeling that you think 9 meters is on the small side, when it is in fact the fattest rocket ever flown. It isn't an easy thing to handle nine meter body segments without damaging them, and the first prototypes even looked like amateur school projects put together from discarded soda cans. The biggest hurdle Starship faces is the ambition to make it reusable. If the booster is to land unharmed it can't be allowed to reach too high a velocity before stage separation, or the fuel economics goes down the drain. Saturn five didn't have to take that into account. Personally I hope that Musk will make a disposable second stage to maximize payload and prove what the launch system can do. Thanks again. The diagrams were great.
Saturn v was 10 meters, but I get your point.
@@EagerSpace I've been at Kennedy Space Center and stood under the Saturn V, but I didn't remember it being ten meters across. That's awesome. It turns out both starship and Saturn V has almost exactly the same speed at first stage separation, despite one being disposable, and the other not. That is quite surprising to me. I'll be looking forward to your future videos.
To be clear, I think that even at 9 meters, starship is a giant...
But SpaceX has come up with something new in that they are building the rocket right next to the launch site, so their transportation distance is short - only about 2 miles compared to 3.4 miles from the VAB to 39A.
The Saturn V stages came in from remote factories by boat and you need to have a boat big enough for the stage and then deal with the longer transportation path and lifting them back vertical. With starship, they're just driving it down the road so you can deal with bigger size if you want to. Still a big PITA, but possible.
Blue Origin also has a factory that's close, though by my measurement it's 11 miles to LC-36. To be fair, the SpaceX roberts road facility at Kennedy is about 7 miles from 39A.
My personal guess is that they'll stick at 9 meters for a while but I've been pretty wrong on my predictions about what SpaceX will do in the past.
@@EagerSpace Great conversation. The government funding of the pioneering programs in the sixties made it necessary to spread the manufacturing over many states. (I can warmly recommend the mini-series "From the Earth to the Moon") It seems that there are few things Musk can't do when he sets his mind to it, but his dream of colonizing Mars is completely unrealistic. Starship is still a very promising tool for hauling heavy stuff to LEO and beyond, especially Starlink, space stations, telescopes and military hardware.
I recommend from the earth to the moon because I think it captures the time so well.
I think colonizing Mars is technically feasible, but there are many many concerns about doing it beyond the technical.
i do thinkinthe future the 25 and greater sizes willc oeminto play when he wants to do stations, followign them out for usable area will be insne withte length and the girls total
I dont think there is any such thing as "too big" for the market thanks to starlink. The less launches they do with more satellites per launch, the more money they make. They really have created their own market for starship. As for other commercial stuff, maybe? But with the amount of tug companies coming online and the fact that not many customers are in an urgent hurry, I think most commercial customers would be perfectly fine with rideshares and tugs. SpaceX already stole the smallsat market with this model on falcon 9, so it's just a matter of scaling up. There are also commercial payloads which require starship, such as VAST and Gravitics for launching large commercial station modules. Whether the commercial space station model will be successful is yet to be seen, but there are quite a number of very expensive, low mass products that can only be manufactured in 0g and im sure more will be discovered with the wider availability of "cheap" 0g testing environments. Less space hotels for the rich and more advanced manufacturing facilities will be the main drive for these commercial stations. Build it and they will come.