3 ms·

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

by 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.
- rrmm 6y ago
  I'm not sure I can agree with your priorities here, but fair enough. Would be nice to see some progress.
- wcarey 6y ago
  How much HTP would you need for the launch escape system?
- chipsa 6y ago
  Crew Dragon carries 3 klbs, or 1.4 tons of hypergols. It doesn't just use those tanks for RCS, but also for the abort system. Also, Crew Dragon is closer to 14 tons at landing.
  - lutorm 6y ago
    Indeed. If you want to switch to a less efficient propellant, you also have to explain how to make the launch escape system work with it, otherwise you've traded the extra safety of not having to handle hypergols for a massive extra risk in a less capable escape system.
- dralley 6y ago
  HTP may be (comparatively) non-toxic but that doesn't mean it's necessarily less dangerous. The Kursk (Soviet ballistic missile submarine) was sunk by a malfunctioning HTP torpedo.
  - jabl 6y ago
    Having an oxidizer that easily starts to exothermically decompose sounds extremely dangerous. This was pointed out as the main factor why HTP "lost" to NTO/IRFNA as the storable oxidizer of choice already back in Clarks Ignition (1972). The toxicity of NTO is bad, extremely so, and everyone knows it. But having your oxidizer tank suddenly go boom on its own accord is even worse.

by rrmm 6y ago

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.

rrmm 6y ago
I'm not sure I can agree with your priorities here, but fair enough. Would be nice to see some progress.
wcarey 6y ago
How much HTP would you need for the launch escape system?
chipsa 6y ago
Crew Dragon carries 3 klbs, or 1.4 tons of hypergols. It doesn't just use those tanks for RCS, but also for the abort system. Also, Crew Dragon is closer to 14 tons at landing.
- lutorm 6y ago
  Indeed. If you want to switch to a less efficient propellant, you also have to explain how to make the launch escape system work with it, otherwise you've traded the extra safety of not having to handle hypergols for a massive extra risk in a less capable escape system.
dralley 6y ago
HTP may be (comparatively) non-toxic but that doesn't mean it's necessarily less dangerous. The Kursk (Soviet ballistic missile submarine) was sunk by a malfunctioning HTP torpedo.
- jabl 6y ago
  Having an oxidizer that easily starts to exothermically decompose sounds extremely dangerous. This was pointed out as the main factor why HTP "lost" to NTO/IRFNA as the storable oxidizer of choice already back in Clarks Ignition (1972). The toxicity of NTO is bad, extremely so, and everyone knows it. But having your oxidizer tank suddenly go boom on its own accord is even worse.