SpaceX Starship / Super Heavy Discussion Thread

Miscellaneous and Personal Stuff I Must Share
21

I am a huge fan of the way this rocket is being built. Its an MVR - a Minimum Viable Rocket. Theyre trying to learn specific things, so they built the cheapest functional vehicle they could to test it, and built another one with an isolated team with different detailed designs, so they can test which works best.

An orbital version of this is going to be a lot more expensive and take longer to build. Or for this one to be retrofitted with a heat shield and other orbital hardware. Why risk all of that time, money and effort if the basic design might still need work? This is agile rocket development. That being the case, I think we should be prepared for the odd failure along the way. When you build them fast and cheap, you can refactor and iterate often. (-:

I’ve been thinking about how cheap this might all get in the short and medium term. I don’t see $100/kg any time soon, but I’d like to be wrong.

Consider the first operational Starship system. Musk says he can build it for $230 million. Let’s just go with that. Also, they need to recoup several billion in development costs, and do it before the inevitable competition arrives and drives down prices.

At first, they will not have the data to know how often a Starship and Superheavy can fly without serious refurbushment or replacement. They have almost no operational data on the Raptor engine other than the test stand and a few short hops. And the first one or two Starships and SuperHeavys will no doubt be
will be torn down for inspection.

Maybe after the first few flights they’ll set the TBO to ten flights, or twenty, or a hundred. We don’t know. But let’s say every ten flights the thing needs a rebuild that costs a third of its value, and has to be retired at 100. So, $230 million / 100 flights is already 2.3 million per flight. Add in the rebuilds, and it’s 3.1 million. A million for fuel per flight, pad rental is currently about a million, but with volume maybe that will get better. Launch insurance… I have no idea. It depends on what is being launched, and if humans are involved. How do you even get launch insurance for 100 people at a time, in a rocket with an iffy escape system? Maybe after 1000 accident free launches…

Then there’s recouping the development cost plus profit. If you want to get your $2.5 billion or whatever back in 100 flights, that’s $25 million per flight. Then there’s the cost of money, some accidents or test failures along the way, whatever. Nothing is ever as cheap as you think.

I’m going to bet that the first Starship flights will not be charged out for less than a Falcon Heavy. It will be much cheaper per Kilo, but the overall cost will be right around there. The thing is, it then has real potential to slowly come down in price, or to rapidly come down in price if competition shows up or the launch market grows substantially allowing fixed costs to be amortized over more launches.

When you get to the point of Mars launches and your’e talking about six refuelings, plus tying up several Starships for years, the costs will not be cheap. I mean, compared to old school rockets on the “cost plus and retainer” plan it’ll be a revolution. But it won’t be crazy cheap for a long time. There would have to develop a very large launch market so vehicles could be flown in large numbers.

Elon says SpaceX is about to start building 500 Raptors per year. That’s about enough for ten Starship/Superheavy combinations. That’s a lot of rockets. These things are reusable, so in year 2 SpaceX will have 20. Then 30. Is the launch market big enough to support that? If they each can fly ten times per year, there would be 300 SuperHeavy launches three or four years after the start of production. That seems like a lot, even if they retire the Falcon 9 series and use Starship/SH for everything. If a large market for space launch develops, I think it will take longer than that. Maybe Starlink flights will help pick up the slack if there is some.

22

To be clear, I don’t expect this too soon, either–but I also don’t expect it take decades.

I’m curious how the economics all play out. SpaceX will need to grow the market to really drive prices down to where they want. Ideal would be a long term delivery contract, from NASA or otherwise. And the farther the better–you really get a high flight rate when doing orbital refueling, which you need for anything but LEO. One flight to the Moon means 10 or so launches. Charge $5k/kg for anything you want on the Moon’s surface.

Until the competition shows up, SpaceX will also want some kind of variable pricing. Even though the cost per flight is constant to SpaceX, they’ll want to charge their customers what they can afford, so to speak. Some tiny company only has $20M to spend on launch? Great, they’ll put up a 5 t satellite for that. Some big telecom wants to launch a massive 50 t geostationary bird? That’ll cost $150M. Etc. No matter what the price point, SpaceX should be able to easily undercut the competition, but they also need to recoup their investment.

23

I find these threads interesting, in large part, because I have a son who is an aero engineer. I acknowledge that he is quite biased against SpaceX. He used to work for ULA, and he felt SpaceX was allowed to compete unfairly, free of many of the constraints placed on ULA in order to encourage competition. He also bridled at the constraints imposed on ULA by its own corporate structure. (He no longer works at ULA, but for a satellite builder.) My son seems to have a strong dislike for Elon Musk as a person, believing that he is more about hype than science. Sometimes it can be hard to discuss SpaceX w/ my son, because he can go off on his dislike for Musk, as opposed to discussing the tech.

Like I said, I admit my primary source of info is biased. But this thread or a predecessor led me to ask his opinion about the new Falcon heavy when I saw him a couple of weeks ago. He pretty quickly takes the conversation to a place my lawyer mind has a hard time following, but as best I gathered, his biggest complaint was that the “heavy” wasn’t as heavy as it ought to be. He has always been about getting payload to orbit cheaply, and he doesn’t think this rocket is big enough to accomplish that. I think he identified some other proposed vehicle which would be more suitable. Not sure of the maker or status.

He also had concerns about the reusability, questioning the costs of refurbishing and, lacking those costs, the reliability. In short, he feared that cheap and rapid reusability would ultimately cost lives. And the striving towards infallibility was largely responsible for what was reported as excessive costs associated with traditional launch vehicles.

Like I said, this is a topic I find interesting, but lack the science and math to get too deep into. And I’d appreciate it if folk didn’t try to persuade me that my son is a crank or a fool. (He may be either or both - like his old man! ;)) I’d appreciate any thought which might contribute to my being able to engage in future such discussions.

24

Elon Musk comes across as a nerdy ass to me (and others) so your son is hardly alone in that. Legacy monopolies never like the freedoms allowed to new competitors that get introduced by government. That said, he’s managed to get a new rocket built, reused and flown over and over again while engaging the public. That’s way more than ULA or ESA ever managed to do.

25

Yeah - a problem discussing these things w/ my son is inability to leave his feelings for EM the person out of discussions of the product.

I think his objection to the rocket is that it isn’t what he thinks is most needed for space exploration/exploitation. And - as a quality engineer - he seems to have concerns about the speed/costs. But a considerable part (most? all?) of that might be sour grapes.

26

Their choice of methane isn’t really a cost thing, it’s a performance thing. Methane lies roughly halfway between liquid hydrogen and RP-1 in terms of performance and usability. So it’s not nearly as difficult as LH2 to deal with, but gives significantly better performance than RP-1.

27

I can see how one could have the first complaint or the second complaint but both are difficult to have at the same time. Going cheaper and faster will cost lives, sure. The alternative being infallibility, which is largely responsible for excessive costs of traditional launch vehicles?

28

There is a good argument to be made that SpaceX’s way will ultimately be safer. Reused rockets seem dangerous today because the effects of the last flight may have done damage that isn’t spotted for the second flight. And that is kinda, sorta true for a brand-new rocket that’s never done that kind of thing before, but as operational data is collected, the effects of spaceflight and re-entry on the vehicles will become much better understood, and once it is the reused vehicles will be seen as more reliable. For one thing, you know there are no manufacturing defects that will cause a rapid disassembly the first time the thing tries to lift off the pad or when it hits Max-Q.

After all, would you want to be the person to first fly an airplane off an assembly line, or would you rather fly it after it’s had maybe 500 hours of proven flight?

Also, lower cost of flight means more flying, which means a more rapid understanding of risks and failure modes. The SLS, at maybe 1-1.5 billion per flight, will only fly maybe one every year or two, and always with a new vehicle. That makes every one of those flights experimental, with all the risks that brings. And at a flight rate that low, there could be hidden, potentially fatal defects that do not surface for a long time after everyone has become complacent. See: Columbia disaster.

And the general refusal of many good engineers in believing that SpaceX can be ‘for real’ in terms of its radical improvements in cost, reusability, etc. is a good display of the adage that science advances one funeral at a time. When you’ve been working in a field for years or decades, surrounded by brilliant people, it’s easy to accept that your way of doing things must be optimal, and anyone that comes along with an idea for anything other than tinkering around on the margins is scoffed at. How could a guy like Elon Musk be smarter than all the engineers at NASA, ULA, etc? (the answer is that they aren’t, but they are working within a sclerotic system that suppresses innovation).

29

Good point. I’ll bring that up when he visits over Thanksgiving. And I’ll try to get a better idea of what functionality he thinks is needed that the Falcon lacks.

30

SpaceX never does things for just one reason. We can argue about the proper order of things, but methane wasn’t chosen just because it’s higher performance than RP1, or just because it’s cheap for that matter. It’s several reasons all at once.

As a propellant, methane:

  • Is one of the few fuels compatible with full-flow staged combustion. RP1 can’t be used here as it turns to a gooey mess when partially combusted.
  • Is pretty easy to model computationally. There are “only” around 300 intermediate chemical species during the combustion process. The only easier one is hydrogen.
  • Has a pretty good density, making for fairly compact tankage. Not as good as RP1, but much better than hydrogen.
  • Is cryogenic. Which means that it can be subcooled. RP1 can be cooled a little but the viscosity goes way up. Subcooling gives a density advantage, which translates to more compact tankage and higher thrust engines.
  • Is non-toxic. All the hydrocarbon fuels are ok here.
  • Can be synthesized on Mars. It’s really almost an ideal fuel in this application, because getting hydrogen (water) is going to be a limiter here, whereas atmospheric CO2 is easy to come by, and adding the extra carbon gets you some extra oomph per unit hydrogen. At the same time, it has an easy synthesis process.
  • Has high material compatibility. It isn’t corrosive like some fuels, but also doesn’t cause metal embrittlement like hydrogen.
  • Is, like stainless steel, such a common material that there’s lots of ambient knowledge on how to work with it. You can order it by the tanker load with no trouble.

Probably some others I’m not thinking of. And then of course the aforementioned cost and performance. Any one of these reasons, alone, would not close the case on it. Really, for most of them, there’s another fuel that’s better. But all of them together makes methane a real standout.

Incidentally, methane isn’t really halfway between RP1 and LH2, performance-wise. It’s more like 1/3 of the way. And even then, it only does so well (on Raptor) because it’s easier to build an engine that gets close to the theoretical limit. You aren’t wrong that methane is good because it’s a higher performance fuel than RP1 without all the disadvantages that LH2 brings, but there’s more to it than just that.

31

Aerospace is such an unforgiving subject that you can’t possibly be a crank or fool and get anywhere. The groups that have built a successful orbital rocket makes a very short list. This goes both way, of course–whether or not one thinks Musk is the reincarnation of PT Barnum, the fact is that SpaceX has made it to orbit. Their vehicles work.

In any case, I don’t want to turn this into an anti-ULA thread. SpaceX is developing Starship virtually on their own. Whether it succeeds or fails won’t depend on anyone but themselves. Their rapid iteration strategy seems to be working so far, though.

I’m not sure what specifically what would help you have productive conversations with your son, but I’m happy to answer any technical points as best I can.

32

I was just trying to make my point that methane wasn’t chosen because it’s cheap, but rather because it’s better than RP-1 in a lot of ways(including suitability for full-flow staged combustion engines), and a lot easier to deal with than LH2. I imagine that considering the advantages methane has, the fact that it’s probably cheaper than RP-1 and LH2 is just icing on the cake.

33

I’m disappointed with the stainless steel, to be quite honest. When I think stainless, I think of the covers of the pulp sci-fi I read as a kid, or even spacecraft you see in modern movies. While I know that it can’t be seamless, I want it to look seamless, and this thing looks like something Andy Griffith might have put together in Salvage 1.

34

That’s because, being a proof-of-concept model, it was welded together out of a bunch of small, rolled plates. Rivets would have been far cooler. :slight_smile:

The next ones will be out of one big rolled plate and thus, have only one long seam. You can turn it to the back like you do the bad side of a Christmas tree.

35

You can’t look at these things in isolation, though. If some hypothetical fuel had all the same benefits as methane except it was 10x the cost of LH2, then SpaceX wouldn’t have chosen it. They’d have used LH2 or stuck with RP1. They might have even gone with an entirely different architecture; say, something resembling Sea Dragon. They might have gone in a different direction than Raptor; say, Russian-style oxygen-rich staged combustion instead of full-flow.

That methane is really cheap and not just pretty cheap is icing, but they couldn’t have achieved their price targets if they were going backwards on propellant cost.

36

Oh, sure, but I have never had the impression that the decision-making process was geared around cost- I think that the cost benefits are more of a serendipitous thing; had it cost the same as LH2, they might have gone with methane anyway, considering its easier usage.

37

They went with methane in large part because id you want to make fuel on Mars, methane is the best way to go. When your entire company is built around building a colony on Mars, you better choose a rocket fuel that can easily be made there.

38

One of Musk’s earliest public talks on the subject:

He mentions the other things too, like synthesis on Mars and the performance and relative ease of use. But cost was a concern from the beginning, and one might argue that it was the single factor that started them down that road, with the others acting more as things that would have invalidated it had they gone the other way (but, conveniently, did not).

40

Starship is moving along nicely with its test program.

But I didn’t appreciate how huge the useable interior is until I watched this video. Of course the fittings this guy has envisioned is pure speculation but it gives you an idea of the amount that can be transported with such a large ship.

41

Well, I guess we were hoping a little too much:

Also, Kamala Harris has been appointed chair of the National Space Council:

None of this is good news. Elon better start making contingency plans.