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Soyuz still uses hypergols on the service module. SpaceX has no separate service module (just the trunk which has no propulsion), which saves money as the whole

Soyuz still uses hypergols on the service module. SpaceX has no separate service module (just the trunk which has no propulsion), which saves money as the whole propulsion system can therefore be reused. If the Soyuz used peroxide for the service module, it’d weigh far more due to lower performance. Peroxide has serious limitations in performance (and, like all strong oxidizers and monopropellants, has serious safety concerns by itself and can burn you). SpaceX does nothing out of pure tradition, if that hasn’t been made clear by their approach so far. The future is not hypergols, but there are legitimate reasons for it today.

avmich 6y ago
Kliper is a relatively modern design, which, while admittedly not produced in metal, used much more benign components for RCS. And Kliper also doesn't have a separate service module. One can always say "but Klipper is a paper spacecraft". Of course, nothing is perfect. Buran can be brought as an example, and arguments against that could be broght up - "oh, it's too old". The point still stands - it's possible to not use toxic components, it's desirable - and it's not done. In my opinion, performance arguments - for a relatively low delta-V system - aren't convincing. After all, Crew Dragon is much bigger and newer craft that Soyuz.
- chipsa 6y ago
  Paper spacecraft can do anything. Buran was designed for the same mission lengths as the Shuttle, on the order of a few weeks at most, not half a year or more. For long mission durations, storable hypergolics are the way to go for now. We don't have good flight time on anything else, and we need that for something we're putting crew on.
  - avmich 6y ago
    > For long mission durations, storable hypergolics are the way to go for now. Soyuz is a counterexample which flies for decades. Lockheed's engineers working on orbital fuel storage (Advanced Cryogenic Evolved Stage) will also point that it's not a law of physics.
avmich 6y ago
> SpaceX does nothing out of pure tradition This deserves a separate reply. SpaceX - correctly - speeds up the process by maximally reusing the known solutions for the problems - this not only makes development faster, but saves a whole lot of money on testing the variants which will be found not working. I disagree that SpaceX does nothing out of pure tradition. In many areas, where invention is hard, unlikely and expensive, SpaceX instead opts to optimize the known solutions rather than invent new ones. Practically everywhere - landing first stages, full-flow combustion Raptor, reusing Dragon, all of that has good precedents in Delta-Cliper, RD-270, Gemini and VA TKS - SpaceX makes a right commercial decision to use proven technologies, which brings us results and doesn't break the bank. Note that truly innovative things, like spinning detonation wave engines, are still in the research labs, and not - at least in a big way - in the SpaceX factories. That's correct way to go considering that we have and know a lot already which we don't use fully. > if that hasn’t been made clear by their approach so far. No it hasn't. They just need to be read differently. The fact that they brought - well-tested and beneficial - traditions from computer industry into rocketry doesn't make them doing everything strictly from the first principles.

avmich 6y ago

Kliper is a relatively modern design, which, while admittedly not produced in metal, used much more benign components for RCS. And Kliper also doesn't have a separate service module. One can always say "but Klipper is a paper spacecraft". Of course, nothing is perfect. Buran can be brought as an example, and arguments against that could be broght up - "oh, it's too old". The point still stands - it's possible to not use toxic components, it's desirable - and it's not done. In my opinion, performance arguments - for a relatively low delta-V system - aren't convincing. After all, Crew Dragon is much bigger and newer craft that Soyuz.

chipsa 6y ago
Paper spacecraft can do anything. Buran was designed for the same mission lengths as the Shuttle, on the order of a few weeks at most, not half a year or more. For long mission durations, storable hypergolics are the way to go for now. We don't have good flight time on anything else, and we need that for something we're putting crew on.
- avmich 6y ago
  > For long mission durations, storable hypergolics are the way to go for now. Soyuz is a counterexample which flies for decades. Lockheed's engineers working on orbital fuel storage (Advanced Cryogenic Evolved Stage) will also point that it's not a law of physics.

avmich 6y ago

> SpaceX does nothing out of pure tradition This deserves a separate reply. SpaceX - correctly - speeds up the process by maximally reusing the known solutions for the problems - this not only makes development faster, but saves a whole lot of money on testing the variants which will be found not working. I disagree that SpaceX does nothing out of pure tradition. In many areas, where invention is hard, unlikely and expensive, SpaceX instead opts to optimize the known solutions rather than invent new ones. Practically everywhere - landing first stages, full-flow combustion Raptor, reusing Dragon, all of that has good precedents in Delta-Cliper, RD-270, Gemini and VA TKS - SpaceX makes a right commercial decision to use proven technologies, which brings us results and doesn't break the bank. Note that truly innovative things, like spinning detonation wave engines, are still in the research labs, and not - at least in a big way - in the SpaceX factories. That's correct way to go considering that we have and know a lot already which we don't use fully. > if that hasn’t been made clear by their approach so far. No it hasn't. They just need to be read differently. The fact that they brought - well-tested and beneficial - traditions from computer industry into rocketry doesn't make them doing everything strictly from the first principles.