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Do you think NASA considers it an issue? They seem pretty ok with it and have plenty of experience with it. The robustness of the system is hard to give up.

by rrmm 6y ago

Do you think NASA considers it an issue? They seem pretty ok with it and have plenty of experience with it. The robustness of the system is hard to give up. And fueling and recovery has always been a large production requiring attention to detail. Has NASA or DARPA put out any requests for a next-gen RCS fuel replacement?

avmich 6y ago
> Do you think NASA considers it an issue? Maybe not, but they'd better do. The experience can be changed - SpaceX, for example, convinced them that loading fuel is better done with crew onboard. The point is, it's better not to have toxic components close to humans, and it also can be done technically. There could be reasons otherwise, but so far I don't see them particularly convincing, robustness and all notwithstanding.
- NikolaeVarius 6y ago
  Reliability and performance is literally the reason that the risk to use hypergolics are made. "I don't think its a good reason to use a thing if we ignore the reasons to use the thing"
  - avmich 6y ago
    I think you can have adequate reliability performance and win on safety with a different choice of propellants. I also think general history of technology - including space technology - supports this point of view.
    - NikolaeVarius 6y ago
      You're not arguing anything. You're saying "I think something else can be good too". Until you literally give an actual engineering (comparison of performance/reliablity/etc) reason that hypergolics are the wrong choice to make, this is effectively saying that "something should be different because I think so"
      - deleted 6y ago
        [deleted]
      - avmich 6y ago
        > Until you literally give an actual engineering (comparison of performance/reliablity/etc) reason that hypergolics are the wrong choice to make, this is effectively saying that "something should be different because I think so" As with many discussions, we talk here mostly qualitative differences. Quantitative differences are harder to get by - for example, back of the envelop calculation says that 30 kg of peroxide in Soyuz landing capsule could be, roughly, replaced with 15 kg of hydrazine, so you'd have a 15 kg mass saving here, but in general actual engineering calculations are harder. I wish they wouldn't be such. Given those very crude estimations and the practice, which shows there are no big unforeseen problems, we have a valid arguments for the alternative. It's an engineering argument, an estimation and not necessarily full calculations, and it's not effectively an arbitrary opinion. You may finally decide the issue using hard numbers, but since we don't have them now, the question stands.
- rrmm 6y ago
  Non-toxic would be better than toxic. What would be the options? Compressed cold-gas (which don't have much kick, and require compressed gas which carry their own dangers). You could go with a monoprop Hydrazine which would eliminate half the toxic stuff. There are also some new developments here: hydroxylammonium nitrate (HAN)/water/fuel ? No idea of the trade offs there. Biprop hydrocarbon/gaseous compressed oxygen? Presumably that'd require an ignition source (and power source). How do you see that trade off? Do you consider high-test peroxide non-toxic? (It certainly has a different risk profile, but is nasty stuff on contact with about anything that can oxidize). The decomposition would also make storage and rotation a consideration.
  - avmich 6y ago
    > What would be the options? Soyuz uses straight hydrogen peroxide, I believe, 82% concentration. For 3 tons capsule it takes 30 kg of peroxide - monopropellant - to land. Buran is still the example of a high tech option - it used LOX and kerosene for RCS, the biggest trick was to keep LOX liquid for a month-long missions. It was done with mid-1980 technologies. Kliper planned to use LOX and ethanol. The craft wasn't completed in metal though. One has to remember that hydrogen peroxide - the rocket concentrations are called HTP, high test peroxide - can be used as an oxidizer, after a catalytic decomposition - and after decomposition HTP is easily hypergolic with fuels. "Hypergolic" doesn't mean "nitrogen-containing, long-storing and toxic", it means "self-igniting" - and it could be non-toxic (or at least HTP toxicity is on the whole different level that hydrazine's one). To come back from orbit you don't need too much delta-V. So Soyuz uses 30 kg of peroxide, maybe it would use 15 kg of hydrazine for the same effect - you're saving 15 kg in a 3 ton spacecraft but losing on toxicity. Similarly, Crew Dragon is a heavier craft, flying on a bigger F-9 rocket, it can probably allow for some extra mass spent for RCS fuel in order to make it non-toxic. > You could go with a monoprop Hydrazine which would eliminate half the toxic stuff. Hydrazine is, I think, a way bigger half. NTO is comparatively benign... not so carcinogenic. But still lethally dangerous :( . > Biprop hydrocarbon/gaseous compressed oxygen? Was done at least. Yes, it would require extra systems. You think it can't be done? > Do you consider high-test peroxide non-toxic? Comparing to hydrazine - yes. > The decomposition would also make storage and rotation a consideration. Yes. Have to chill it, take care while in storage and keep tanks extra clean. But still.

by rrmm 6y ago

avmich 6y ago

> Do you think NASA considers it an issue? Maybe not, but they'd better do. The experience can be changed - SpaceX, for example, convinced them that loading fuel is better done with crew onboard. The point is, it's better not to have toxic components close to humans, and it also can be done technically. There could be reasons otherwise, but so far I don't see them particularly convincing, robustness and all notwithstanding.

NikolaeVarius 6y ago
Reliability and performance is literally the reason that the risk to use hypergolics are made. "I don't think its a good reason to use a thing if we ignore the reasons to use the thing"
- avmich 6y ago
  I think you can have adequate reliability performance and win on safety with a different choice of propellants. I also think general history of technology - including space technology - supports this point of view.
  - NikolaeVarius 6y ago
    You're not arguing anything. You're saying "I think something else can be good too". Until you literally give an actual engineering (comparison of performance/reliablity/etc) reason that hypergolics are the wrong choice to make, this is effectively saying that "something should be different because I think so"
    - deleted 6y ago
      [deleted]
    - avmich 6y ago
      > Until you literally give an actual engineering (comparison of performance/reliablity/etc) reason that hypergolics are the wrong choice to make, this is effectively saying that "something should be different because I think so" As with many discussions, we talk here mostly qualitative differences. Quantitative differences are harder to get by - for example, back of the envelop calculation says that 30 kg of peroxide in Soyuz landing capsule could be, roughly, replaced with 15 kg of hydrazine, so you'd have a 15 kg mass saving here, but in general actual engineering calculations are harder. I wish they wouldn't be such. Given those very crude estimations and the practice, which shows there are no big unforeseen problems, we have a valid arguments for the alternative. It's an engineering argument, an estimation and not necessarily full calculations, and it's not effectively an arbitrary opinion. You may finally decide the issue using hard numbers, but since we don't have them now, the question stands.
rrmm 6y ago
Non-toxic would be better than toxic. What would be the options? Compressed cold-gas (which don't have much kick, and require compressed gas which carry their own dangers). You could go with a monoprop Hydrazine which would eliminate half the toxic stuff. There are also some new developments here: hydroxylammonium nitrate (HAN)/water/fuel ? No idea of the trade offs there. Biprop hydrocarbon/gaseous compressed oxygen? Presumably that'd require an ignition source (and power source). How do you see that trade off? Do you consider high-test peroxide non-toxic? (It certainly has a different risk profile, but is nasty stuff on contact with about anything that can oxidize). The decomposition would also make storage and rotation a consideration.
- avmich 6y ago
  > What would be the options? Soyuz uses straight hydrogen peroxide, I believe, 82% concentration. For 3 tons capsule it takes 30 kg of peroxide - monopropellant - to land. Buran is still the example of a high tech option - it used LOX and kerosene for RCS, the biggest trick was to keep LOX liquid for a month-long missions. It was done with mid-1980 technologies. Kliper planned to use LOX and ethanol. The craft wasn't completed in metal though. One has to remember that hydrogen peroxide - the rocket concentrations are called HTP, high test peroxide - can be used as an oxidizer, after a catalytic decomposition - and after decomposition HTP is easily hypergolic with fuels. "Hypergolic" doesn't mean "nitrogen-containing, long-storing and toxic", it means "self-igniting" - and it could be non-toxic (or at least HTP toxicity is on the whole different level that hydrazine's one). To come back from orbit you don't need too much delta-V. So Soyuz uses 30 kg of peroxide, maybe it would use 15 kg of hydrazine for the same effect - you're saving 15 kg in a 3 ton spacecraft but losing on toxicity. Similarly, Crew Dragon is a heavier craft, flying on a bigger F-9 rocket, it can probably allow for some extra mass spent for RCS fuel in order to make it non-toxic. > You could go with a monoprop Hydrazine which would eliminate half the toxic stuff. Hydrazine is, I think, a way bigger half. NTO is comparatively benign... not so carcinogenic. But still lethally dangerous :( . > Biprop hydrocarbon/gaseous compressed oxygen? Was done at least. Yes, it would require extra systems. You think it can't be done? > Do you consider high-test peroxide non-toxic? Comparing to hydrazine - yes. > The decomposition would also make storage and rotation a consideration. Yes. Have to chill it, take care while in storage and keep tanks extra clean. But still.