Why SLS is still OUTCLASSED by a 55 Year Old Rocket!
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- Опубликовано: 24 ноя 2022
- Today we're taking a look at the SLS, and answering the question of why it is substantially less capable than the 55-year-old Saturn V. To be fair, there are a lot of differences between these rockets but this video is looking at how the core design of the SLS differs from the Saturn V at it's most fundamental level.
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My thoughts on this: the ICPS setup, where you used a smaller upper stage, was done as a cost cutting measure. They were given an impossible deadline, with not much money to make it happen, do they figured, okay, we'll use this to meet the requirements, then put a big upper stage on later down the line (Even studies for hydrocarbon core SLSs had this option for commercial upper stages in the trade space, options included the DCSS, Falcon 9 S2, the Ares I upper stage, I think the Zenit upper stage as well, among others). This large upper stage, the EUS, is in development right now. In the end, this approach... didn't work. Surprise surprise, building a SHLV is hard. Especially when you're pinching pennies. I'd argue that the flat budget actually made SLS more expensive than it would have been if they followed a more traditional dev curve. The RS-25's vacuum performance isn't a huge concern, as it's still extremely good, even better than some older hydrolox pure-vacuum engines. The staging arrangement comes from the space shuttle, yes, but that doesn't mean it's not advantageous. No new large hydrocarbon engines had to be developed. No expensive GSE mods had to be installed, or RP storage at LC-39B(it is worth mentioning that the hydrocarbon core studies mentioned that while the GSE cost would be expensive upfront, it would be cheaper operationally since it's simpler and not designed with reuse in mind). Plus, SLS is actually a hell of a lot lighter than the Saturn V. Fully loaded, an SLS Block 2 would be around 700 tons less than a fully loaded Saturn V, and can send even more payload to TLI. Ariane 5 uses a similar design to SLS. H-II/A/B/III uses a similar design to SLS. Adding a third stage adds more complexity and increases cost. The only rockets I can think of off the top of my head that used an "optimal" staging configuration are Proton and Saturn V. So while yes, the explanation given absolutely makes sense, the staging arrangement of SLS does make sense.
Do the SRB´s with their lower isp also play a part in this effect?
That would play a part, though using SRBs makes a lot more sense for the design than not having a substantial second stage
A society built around a nearly universal ignorance of how the money system works is rather far from ideal. It clearly can't be said to benefit no one so it's not going anywhere but thank you for explaining how it influenced this program. Today, things take far longer to complete, cost many times as much, compared to the fifties and sixties and may or may not be very good thanks to corruption and just plain modern politics. I suppose we can be thankful that good things do still happen.
"I believe that this Nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to Earth."
Actually developing SLS costs way less than Saturn V and the Artemis program is still cheaper than the whole Apollo program with much-much more component. Artemis not only includes SLS and Orion, but Gateway, HLS, SLD, rovers, satellites, space suits, other auxiliary missions sent on other rockets, etc.
The thing what pumped up Apollo's costs is the time constraint set by Kennedy. Artemis's deadlines is rather flexible than Apollo's. Also Artemis was often underfunded, NASA got the money later when they actually needed while Apollo basically got all the money in time when they needed. This - ironically - also creates cost increases: you have to pay the fixed costs - usually the upkeep of the infrastructure, payments, etc.
So yeah, politics involves a lot in those decisions but not only.
I think you missed a lot of key things about SLS which is weird for me considering that you're an aerospace engineer.
One of the key thing is that SLS (and Space Shuttle) is more like a stage-and-half design like R-7 (Soyuz) and early Atlas missiles, rockets. The boosters is like the first stage and the core is like the 2nd. Boosters role is to provide the necessary thrust to get off the pad and get out the most dense part of the atmosphere and the Core's job is to reach orbit (like the 2nd stage of Saturn V). RS-25's are designed for this job and it's have a pretty good 452 sec ISP for that. (In comparison J-2 had 421).
Also NASA intentionally shut down the core on suborbital trajectory. They don't want to play debris bingo with a 85t rocket body (like China do with CZ-5B's Core) and left the circularization to the upper stage. NASA did the same with Shuttle's ET for the same reason. But this stack without any upper stage could capable to launch 95t to LEO. This is more than enough to launch Skylab. (And if the rumors true, it's kinda similar what Starship actually capable at the moment.)
So about the 2nd stage. I'm pretty sure that you know that SLS Block 1 utilize a slightly lengthen and modified DCSS called Interim Cryogenic Upper Stage. And as the name suggests it is just an interim solution. The plan was always to get a properly sized upper stage starting from Block 1B. The first plans was to carry over the EDS (Earth Departure Stage) from the Constellation Project but eventually they chooses to develop the EUS (Exploration Upper Stage). They did it because they want to spare the development cost of J-2X engine and "just" modify the RL-10 engines for SLS needs, because engine development is stupidly expensive. (This is why they choose to use and develop further RS-25's.) I'm not sure why you didn't mentioned EUS at all in the video. It significantly increases the TLI performance, specially with Block 2 upgrades (27t->46t) which is similar what Saturn V had.
Also the using parts from Space Shuttle statement I think need some addition: basically two part was reused from the Shuttle: 16 engines for the first 4 missions (but they were modified, like they got the engine control unit from J-2X development, because the old ECU's was ancient and incompatible with SLS) and some steel cases for boosters. But because the 5th segment, the nozzle was already modified, the tank, avionics, etc. was entirely new design, the tooling for manufacturing is brand new, etc. Not even the alloy is the same for the tank, partially because of manufacturing reasons. (Also it had some performance impact.)
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Use of KSP to actually explain science and engineering and not just to blow things up? What sorcery is this?
SLS is not designed the way it is to save money. It's designed the way it is to keep the manufacturing lines that ran the Shuttle running. It's entirely political because some states heavily relied on the Shuttle program for employment and the congressmen from those states made sure their states would not be ruined by the end of the Shuttle program. So don't think of the SLS as a huge waste of money, think of it as a subsidy for states.