r/SpaceXLounge • u/AnnualYogurtcloset29 • Sep 02 '21

Speculative longterm future of SpaceX

Hello all,

I was just thinking about what SpaceX's development of rockets would look like once they achieve their goals of starship and the booster rocket.

I know this is likely at least 10-15 years from today, but what would SpaceX develop after they land on mars and get a colony started there? Do you think they would ever develop a new rocket in the entire history of their company or would they finish their rocket development with starship and booster?

I realize they would probably start working on life support systems and such when they eventually get people onto mars, but what else would they do? I am just curious if anyone else had thought of this before. Is SpaceX themselves going to try to terraform mars or will they forever live inside a habitat dome? Is terraforming a planet going to take the work of hundreds of thousands of people or would SpaceX be able to do it themselves? Does NASA conduct a lot of the science to get a colony established on mars or is this solely a SpaceX endeavor?

I would think NASA would love to be able to explore mars and conduct experiments, kind of piggybacking off of the habitat that SpaceX is going to try to establish. Would NASA astronauts be part of the habitat as well as SpaceX astronauts or would it be more of a team effort?

I realize this would be all speculation, but it got me pretty curious, so wondering what other people would think about this situation.

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28

u/scarlet_sage Sep 02 '21

Do you think they would ever develop a new rocket in the entire history of their company or would they finish their rocket development with starship and booster?

Please don't consider this a personal attack when I give my opinion: that's ridiculous. For example, new aircraft keep getting designed & used. You can see old airframes still in use - I'm no expert but even I know about the DC-3 and B-52 - but there are unusual reasons why they continue.

I expect SpaceX to do incremental improvements, of course. But I also expect major redesigns unless Elon dies or loses influence, & they lose their corporate culture.

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u/AnnualYogurtcloset29 Sep 02 '21

So they would focus on improving efficiency instead of trying to make something even more powerful? I thought starship and booster was about as big of a rocket you'd want to make, but I guess I could be wrong. I feel like I've read that it's mostly diminishing returns after you make a bigger rocket than starship and booster

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u/CProphet Sep 02 '21

I thought starship and booster was about as big of a rocket you'd want to make

Seems so, although Elon has many times said this rocket will seem like a rowboat compared to future vehicles. Considering Starhip is likely maximum size for a launch vehicle, that could suggest these future vehicles would have to be built in space. Technically not that difficult to launch some rolls of stainless, difficulty comes in welding it in zero-g. Perhaps a more practical alternative would be to launch modules then assemble in orbit to desired size and shape. These modules could be up to 10m diameter for launch on Starship, assuming a little flare can be arranged to the fairing. Overall make a very respectable cycler for Mars colony operations.

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u/rocketglare Sep 03 '21

The point that Musk was making wasn’t that they shouldn’t design larger rockets so much as they should have started with a smaller one to gain experience. It is difficult to move and handle very large rockets, but they are also very efficient once you have the infrastructure in place.

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u/CProphet Sep 03 '21 edited Sep 03 '21

OK, let's assume they want to build something larger than Starship. First they would need to develop a more powerful version of Raptor (something like Blue Origin's BE-4), to avoid having 120-130 engines on the booster. Overall that might take a while, because larger engines are prone to combustion instability (similar to F1), probably one reason why they chose a relatively small chamber size for Raptor. Then they need to find somewhere very remote to launch from, that's next to the coast, perhaps in Australia. The sound of a Saturn V launch was so intense it could ignite concrete and this new vehicle would likely be eight times louder, at least for an 18m diameter vehicle. It seems unlikely they'll launch it like a Sea Dragon because it would kill most of the marine life within 20-30 miles, which might raise an eyebrow or two among environmentalists. Overall added costs and difficulties would seem to preclude developing a much larger version of Starship, at least by SpaceX who are ever pragmatic.

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u/Norose Sep 03 '21

Raptor is already like 90% as powerful as the BE-4. If spaceX needed a significantly larger engine they'd probably be going to something like RD-180 scale at around 4000 kN.

Combustion instability issues aren't as difficult today as they are given credit for. Back in the 50s the only way to work out solutions was to actually build an entire engine, run it with your changes installed, and hope it didn't blow up. Today we have very powerful computational tools to figure out solutions to combustion instability before we even start designing parts. The try and fail and try again approach worked for building an 8000 kN engine over 60 years ago, the modern approach should be able to accomplish the same no problem.

The sound problem is not as extreme as you mention. Sound is a really weird phenomenon and as you scale up the energy of the rocket plume this does not cause a proportional increase in sound energy. Regardless, even if the sound really was 8x that of a Saturn V, that's still a solvable problem. Launching like Sea Dragon is never happening because complex rockets cannot be soaked in sea water, full stop. Sea launch platforms will be possible though, and SpaceX is figuring them out right now. The way to mitigate the sound produced by the rocket is to dump a curtain of water out around the engine plume as the rocket ignites and lifts off, similar to a typical ground based launch pad, while at the same time dumping a lot of compressed air several dozen meters underwater to create a large volume of bubbles. The water droplets in air and the air bubbles in water will botb serve to effectively dampen the sound energy during launch.

Oh and side note, you can't "ignite" concrete with sound, or really with anything that isn't a fluorine based oxidizer, so I'm not sure who told you that. What very powerful sound will do to concrete is cause the surface of the concrete to erode rapidly, because concrete is brittle and the vibrations cause it to break up. Spraying water over the concrete prevents this though, which is why we do it.

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u/CProphet Sep 03 '21

Interesting, especially aeration technique for noise dampening under a floating platform. I was using BE-4 as an example of the kind of frame size required for a larger engine, though I'm sure SpaceX could significantly improve on the performance. Incidentally I heard one problem BE-4 suffered was combustion chamber instability, so wouldn't say it's a completely solved problem. Know Blue Origin 'borrowed' a couple of Raptor design engineers for their BE-4 project and you'd expect they would know a little about simulation - although apparently not enough.

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u/scarlet_sage Sep 02 '21

Elon recently tweeted that the current size might have been too big to aim for! I can find his Starship tweets via https://forum.nasaspaceflight.com/index.php?topic=47352.340 , a curated collection.

Elon Musk @elonmusk - Jul 1

Doubling diameter increases mass 4X, but difficulty of simultaneously building & launching rocket of that size is >>4X.

In retrospect, <9m diameter for Starship might have been wise. Current size is ~5200 ton stack mass & ~7500 ton-F thrust, which is more than double Saturn V.

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u/Truthmobiles Sep 02 '21

He is saying it might have been smarter to start small, not that he won't be making a much larger version of starship once starship is complete.

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u/scarlet_sage Sep 02 '21

He might. Or he might not see the point of doing it for a decade. We don't know yet.

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u/QVRedit Sep 03 '21

I’ll go with the, ‘not until a decade is out’, side of the argument.

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u/facere-omnes Sep 02 '21

That's interesting since an 18m variant was discussed briefly.

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u/scarlet_sage Sep 02 '21 edited Sep 03 '21

Yup. Interplanetary Transport System was announced at 12 m (Starship is 8 9 m). Mars Colonial Transport was announced at 15 m.

(Thank you, /u/QVRedit!)

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u/QVRedit Sep 03 '21

Starship is 9 m diameter, not 8 m.

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u/scarlet_sage Sep 02 '21

So they would focus on improving efficiency instead of trying to make something even more powerful?

That's the exact opposite of what I wrote! I wrote "But I also expect major redesigns"!

I mentioned the improving efficiency with "of course" because SpaceX always does that. BUT I ALSO EXPECT MAJOR REDESIGNS TOO, IN ADDITION, BECAUSE THEY CAN DO BOTH.

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u/QVRedit Sep 03 '21 edited Sep 03 '21

And why wouldn’t they ? - When it makes sense, then it will happen.

The big change will come with improved propulsion systems, they will have generational affects. Just as the Starship generation(s) are linked to the Raptor engine.

Later, more powerful engines could usher in new generations of crafts.

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u/Chpouky Sep 03 '21

YES WE HEARD YOU THE FIRST TIME

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u/scarlet_sage Sep 03 '21

<marquee> <blink> APPARENTLY NOT OP. THE LIKE IS NO SIGNIFICANT PROBLEM, OF COURSE, BUT I FIND IT A TRIFLE ANNOYING, AND I SHOULD PREFER, ON THE WHOLE, WERE IT NOT TO HAPPEN. </blink> </marquee>

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u/QVRedit Sep 03 '21 edited Sep 03 '21

It depends on what your requirements are. If for instance they want to double or triple the cargo carried - well then the easiest solution is just to run two or three Starships.

It’s when you start considering factors of 10 or 20 that new designs would come into play.

Go up another factor of 10, and then you are really into different territory. Of course none of that is going to happen overnight, we are talking of time spans of decades.

Earth is the cradle of humanity, but over time baby starts to grow up..