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Buran was using LOX, storing it for up to two weeks with a cryocooler and a complicated cooling system, Crew Dragon can be rated for hundreds of days and doesn'

Buran was using LOX, storing it for up to two weeks with a cryocooler and a complicated cooling system, Crew Dragon can be rated for hundreds of days and doesn't have the volume/mass/cost to spare. Dreamchaser with its propane/N2O thruster is a better counterexample. They avoided toxic components so it could theoretically land at any airport, making it a strong selling point. There are also new(-ish) hydroxylammonium nitrate based propellants which are storable, better than hydrazine and aren't toxic either.

avmich 6y ago
> Crew Dragon can be rated for hundreds of days and doesn't have the volume/mass/cost to spare. Mass is often an issue with spaceflight. We're arguing about what's better overall, not what's better by all possible criteria. Crew Dragon I'd say has more mass to spare than earlier spacecrafts - because at least of economy of scale and more mass-efficient subsystems.
- phkahler 6y ago
  They could just stick it on top of Falcon Heavy. No mass issues then. AFAIK FH is not going to be man rated any time soon though.
avmich 6y ago
> Buran was using LOX, storing it for up to two weeks with a cryocooler and a complicated cooling system They had insulation and active stirring system, that was enough for 15-20 days. To fly up to 30 days they needed a microcryocooler. http://buran.ru/htm/odu.htm http://buran.ru/htm/odu.htm > Crew Dragon can be rated for hundreds of days Isn't Soyuz rated for 200+ days? > Dreamchaser with its propane/N2O thruster is a better counterexample. Agree, a good example.
jabl 6y ago
Propane/N2O is an interesting combination. It needs to be pressurized quite a lot (the N2O in particular) to stay liquid, ruling it out for large systems like launchers. But for small thrusters, it means the system is self pressurizing, meaning (potentially) less mass and complexity for the entire thing. HAN and ADN are also interesting options. That being said, they should be tested and flown a lot more on cargo launches before they're ready to be put on crafts carrying humans.

avmich 6y ago

> Crew Dragon can be rated for hundreds of days and doesn't have the volume/mass/cost to spare. Mass is often an issue with spaceflight. We're arguing about what's better overall, not what's better by all possible criteria. Crew Dragon I'd say has more mass to spare than earlier spacecrafts - because at least of economy of scale and more mass-efficient subsystems.

phkahler 6y ago
They could just stick it on top of Falcon Heavy. No mass issues then. AFAIK FH is not going to be man rated any time soon though.

avmich 6y ago

> Buran was using LOX, storing it for up to two weeks with a cryocooler and a complicated cooling system They had insulation and active stirring system, that was enough for 15-20 days. To fly up to 30 days they needed a microcryocooler. http://buran.ru/htm/odu.htm http://buran.ru/htm/odu.htm > Crew Dragon can be rated for hundreds of days Isn't Soyuz rated for 200+ days? > Dreamchaser with its propane/N2O thruster is a better counterexample. Agree, a good example.

jabl 6y ago

Propane/N2O is an interesting combination. It needs to be pressurized quite a lot (the N2O in particular) to stay liquid, ruling it out for large systems like launchers. But for small thrusters, it means the system is self pressurizing, meaning (potentially) less mass and complexity for the entire thing. HAN and ADN are also interesting options. That being said, they should be tested and flown a lot more on cargo launches before they're ready to be put on crafts carrying humans.