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Comment by dirtyid | Hacker News Reader

What's is level of complexity relative to something like V2 rocket engine that was suppose to be scaled for 2000 per month. DOD can absorb a lot of exquisit missile engines even during peacetime procurement, I wonder if SpaceX is going to get into the weapons game. Almost everything Elon touches is dual use anyways, wonder what it would take for him flip.

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I don't think the weapons people like liquid cryogenic fuels. They want propellent that is easy to store for years in a vehicle that's ready to launch in minutes or less.

DOD is already SpaceX's biggest customer. It's probably already in the weapons game, but that's not something you're going to hear about, because it would be classified.

DOD is not SpaceX's biggest customers.

Though their launch payloads are often classified, that they're launching DOD payloads isn't classified and given the contracts that are public as reasonable proxies for the ones that aren't, there's simply no chance the DOD's manifest is SpaceX's biggest in terms of launches or dollars.

NASA, for example, launches on SpaceX way more often than DOD. You can easily count the launches yourself by reviewing SpaceX's historical manifest on Wikipedia. I think there have been 6 or 7 DOD launches in the last three years while there have been 15 or 16 NASA launches in the same time period. Some DOD launches are a bit more lucrative than some NASA launches, but the inverse is also true.

You might go on to assert that SpaceX has other DOD projects like its Starlink/missile tracking and E2E cargo (and potentially troop) delivery (and even money for Raptor dev and other smaller programs like the long ago DARPA investment in Falcon 1) but it's clear from various reporting that those are tiny investments compared to a year or three's worth of orbital launches.

Yes, the USG is SpaceX's biggest customer. No, the DOD is not SpaceX's biggest USG customer. That title, for now, belongs squarely to NASA.

Your info is out of date. The tides have turned. Look at the list of launches for 2022. https://en.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_He...

You can see, clearly, far more launches for DOD umbrella agencies than for NASA.

https://www.military.com/off-duty/2020/12/22/these-air-force....

> What's is level of complexity relative to something like V2 rocket engine that was suppose to be scaled for 2000 per month.

Historically, von Braun had to use 70% ethanol - i.e., diluted with water - to avoid V2 engines burning through. So, loss of efficiency. It took quite some efforts to e.g. Glushko with Liliput to switch to kerosene (and cylindrical chamber and flat injector head) - the result was R-7 engines. Some decades of improvements - for example, V2 uses hydrogen peroxide to drive turbopumps, modern engines all use main components, which at least simplifies the engine overall, the closed cycles don't have separate exhaust after turbine, turbopumps are much more efficient (geometry in 1940-s wasn't too good from fluid dynamic point of view, turbine vanes didn't use that high temperature gas, losing in efficiency - here some material development work is important), and others. Raptor has an order of magnitude higher thrust.

A lot more complexity, I'd say.

Just out of curiosity, I look up the chamber pressure of the two engines. The chamber pressure of the V2 engine was 15.45 bar, the chamber pressure of the Raptor engine is 300 bar.

And that's before we get into insane complexities of a full flow combustion cycle vs the open cycle of the V2's engine.

Definitely a lot more complex.

Full flow stage combustion is significantly more complex from my understanding.

the cryogenic methane fueled full flow staged combustion engine of the raptor 2 is in many ways not a good fit for weapons platforms. It's a very purpose built engine for uplifting mass into orbit.

Soviet Union used to deploy R-9 - a rocket which was "always ready", launching within 20 minutes from the command, while using liquid oxygen and kerosene as propellants.

https://en.wikipedia.org/wiki/R-9_Desna

So, it might be considered, I guess. Even though Starship looks rather from another era...

Kerosene makes a lot more sense than methane. The only reason methane makes sense for SpaceX is they intend on manufacturing fuel on mars for the return trip.

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