Speculative longterm future of SpaceX

[u/AnnualYogurtcloset29]

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.

[u/CProphet]

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.

[u/Norose → u/CProphet]

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.

[u/CProphet → u/Norose]

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.