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SpaceX successfully launches two humans into orbit

nasa.gov

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Re: SpaceX successfully launches two humans into orbit

#21

Post by phkahler »

elliekelly wrote: post #16
avmich wrote: post #9

The big and annoying issue with the Crew Dragon design seems to be the chosen RCS fuel (AFAIK, monomethylhydrazine and N2O4), which makes both fueling and clearing after landing a delicate process. Hopefully Crew Dragon proves itself as a capable platform for Earth-orbit transportation, but this fuel issue is a hard one to counter.

Earlier this week when they were de-fueling they mentioned that the "escape system" was still active during that process. Is that because the fuel is potentially dangerous? Tangentially related, can the "escape system" be activated even when the rocket itself hasn't left the ground? I watched the escape system test but IIRC it involved launching and then aborting so the pod that carries the crew was already high off…

A couple years ago they did a pad abort test. Not from a rocket, but from the ground. It got out to sea just fine.

Re: SpaceX successfully launches two humans into orbit

#22

Post by avmich »

Robotbeat wrote: post #13
avmich wrote: post #9

The big and annoying issue with the Crew Dragon design seems to be the chosen RCS fuel (AFAIK, monomethylhydrazine and N2O4), which makes both fueling and clearing after landing a delicate process. Hopefully Crew Dragon proves itself as a capable platform for Earth-orbit transportation, but this fuel issue is a hard one to counter.

Hypergolic fuels have TONS of advantages, including extremely reliable ignition. Basically all crewed orbital spacecraft have used hypergols in some ways. SpaceX's Starship will not use hypergols, although it probably won't be available for years.

> 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.

Re: SpaceX successfully launches two humans into orbit

#23

Post by avmich »

cma wrote: post #17
_Microft wrote: post #15

Earlier quoted context omitted.

One might say that Crew Dragon's days are counted already. Even SpaceX' Gwynne Shotwell (she is SpaceX' long-time COO, in case you do not know her yet) is hoping that SpaceX will fly people on Starship in maybe 3-4 years and she is way more grounded than Mr. Musk. They plan to achieve this unreasonable sounding feat by producing large numbers of Starships and launching them very often to accumulate massive experience…

I wouldn’t say she is that much more grounded: she has also said they are planning on passenger New York Shanghai rocket trips for a price between an economy and business class plane ticket by 2028: https://www.vox.com/2018/4/11/17227036/flight-spacex-gwynne-... Not a prototype or demonstration, a real commercial flight service.

So that's longer than from Alan Shepard's flight to Moon landing. And the task - with all peculiarities - still seems simpler.

I don't think this points to the "ungroundness" of Shotwell. Similar projects were discussed and BOTEd for quite some time. The whole suborbital tourism thing is practically rather similar technology, and we're a couple of decades in the implementation time for that.

Re: SpaceX successfully launches two humans into orbit

#24

Post by NikolaeVarius »

elliekelly wrote: post #16
avmich wrote: post #9

The big and annoying issue with the Crew Dragon design seems to be the chosen RCS fuel (AFAIK, monomethylhydrazine and N2O4), which makes both fueling and clearing after landing a delicate process. Hopefully Crew Dragon proves itself as a capable platform for Earth-orbit transportation, but this fuel issue is a hard one to counter.

Earlier this week when they were de-fueling they mentioned that the "escape system" was still active during that process. Is that because the fuel is potentially dangerous? Tangentially related, can the "escape system" be activated even when the rocket itself hasn't left the ground? I watched the escape system test but IIRC it involved launching and then aborting so the pod that carries the crew was already high off…

Anything involving fuel is dangerous. Demo-2 is first time that humans are on the rocket while its being fueled. The escape system is on while fueling and defueling since those are high risk times for the rocket.

Re: SpaceX successfully launches two humans into orbit

#25

Post by Robotbeat »

avmich wrote: post #22
Robotbeat wrote: post #13

Earlier quoted context omitted.

Hypergolic fuels have TONS of advantages, including extremely reliable ignition. Basically all crewed orbital spacecraft have used hypergols in some ways. SpaceX's Starship will not use hypergols, although it probably won't be available for years.

> 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 nece…

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.

Re: SpaceX successfully launches two humans into orbit

#26

Post by rrmm »

avmich wrote: post #9

The big and annoying issue with the Crew Dragon design seems to be the chosen RCS fuel (AFAIK, monomethylhydrazine and N2O4), which makes both fueling and clearing after landing a delicate process. Hopefully Crew Dragon proves itself as a capable platform for Earth-orbit transportation, but this fuel issue is a hard one to counter.

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?

Re: SpaceX successfully launches two humans into orbit

#28

Post by avmich »

rrmm wrote: post #26
avmich wrote: post #9

The big and annoying issue with the Crew Dragon design seems to be the chosen RCS fuel (AFAIK, monomethylhydrazine and N2O4), which makes both fueling and clearing after landing a delicate process. Hopefully Crew Dragon proves itself as a capable platform for Earth-orbit transportation, but this fuel issue is a hard one to counter.

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?

> 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.

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