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> Basically all crewed orbital spacecraft have used hypergols in some ways. Right, but Soyuz spacecraft is flying since 1960-s, has a half a year orbital stora

by avmich 6y ago

> Basically all crewed orbital spacecraft have used hypergols in some ways. Right, but Soyuz spacecraft is flying since 1960-s, has a half a year orbital storage time, and yet it has no toxic RCS for the capsule. At least that simplifies handling after landing. And it was long since proven RCS doesn't need to use toxic components. The fact that Crew Dragon still uses them points more to the tradition than to the necessity.

Robotbeat 6y ago
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.
NikolaeVarius 6y ago
This is such a weird take on things. They don't just choose to use random chemicals for no reason, there are engineering tradeoffs made. Fuels are extensively well studied and hundreds of thousands of man-hours are spent validating these choices
- avmich 6y ago
  Why weird? Choosing something takes trade-offs - in the case of SpaceX capsules, they chose not to develop non-toxic technoogy, saving some time and money, but making an inferior product. It's not weird, it's their decision - which I'm not sure is good. Given that we hopefully will soon see Starship flying, that may be rather moot point though.
  - NikolaeVarius 6y ago
    Your posts use terms like "inferior" to automatically shift the conversation to the notion that hypergolics are inferior solely because they are dangerous chemicals, and ignore engineering decisions that are made. Its the same as arguing that RP1 engines are inferior to H2 engines because RP1 is based off fossil fuels. It's not relevant to the point.
    - avmich 6y ago
      Dangerousness is relevant, and it's in this aspect which inferiority is mentioned.
      - NikolaeVarius 6y ago
        If you're going to change your argument like this, your post becomes "Hypergolics are less safe for humans than non-hypergolics" Good to know thanks.

by avmich 6y ago

Robotbeat 6y ago

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.

NikolaeVarius 6y ago

This is such a weird take on things. They don't just choose to use random chemicals for no reason, there are engineering tradeoffs made. Fuels are extensively well studied and hundreds of thousands of man-hours are spent validating these choices

avmich 6y ago
Why weird? Choosing something takes trade-offs - in the case of SpaceX capsules, they chose not to develop non-toxic technoogy, saving some time and money, but making an inferior product. It's not weird, it's their decision - which I'm not sure is good. Given that we hopefully will soon see Starship flying, that may be rather moot point though.
- NikolaeVarius 6y ago
  Your posts use terms like "inferior" to automatically shift the conversation to the notion that hypergolics are inferior solely because they are dangerous chemicals, and ignore engineering decisions that are made. Its the same as arguing that RP1 engines are inferior to H2 engines because RP1 is based off fossil fuels. It's not relevant to the point.
  - avmich 6y ago
    Dangerousness is relevant, and it's in this aspect which inferiority is mentioned.
    - NikolaeVarius 6y ago
      If you're going to change your argument like this, your post becomes "Hypergolics are less safe for humans than non-hypergolics" Good to know thanks.