Out of curiosity: What is the liquid temperature range of MMH? of NTO?
I'm slowly developing a list of reasons why a two-stage Earth-orbit departure system makes sense, particularly when using space-storable propellants. I hope to present that reasoning at some point, but at the moment I'm struggling a bit with the extra "degree of freedom" a two-stage system provides. In particular, there's the question of how to choose the sizes for the upper and lower stages.
If you assume departure from L1/L2 [...] only a single storable stage might be needed from L1/L2 onward.
I agree. I'm just not convinced that should be considered an "Earth departure stage." Putting the rendezvous (and thus departure) point is somewhere in cis-lunar space -- whether that's a Lagrange point, DRO, or whatever -- considerably redefines the departure task!
I also believe LEO departure using a "high energy" stage integrated with the launch vehicle (and e.g. loaded with propellant as part of the launch vehicle count down) is certainly going to be more efficient by many measures. That's what makes something like the Exploration Upper Stage proposed for SLS so exciting.
But LEO rendezvous and departure is a meme that seems quite resilient!
whatever launch vehicle you use, I don't see how LEO departure is more efficient. If you are using a storable stage from LEO, then 3.2km/s of your delta-v is provided by storable propulsion, which is less efficient than LOX/LH2.
..I hope to present that reasoning at some point, but at the moment I'm struggling a bit with the extra "degree of freedom" a two-stage system provides. In particular, there's the question of how to choose the sizes for the upper and lower stages.
I have trouble imagining a low cost launch provider that uses a high energy upper stage. Delta, Atlas, Ariane, H-IIA; all are high cost. Further I doubt there is a low cost means of developing a launch system that includes high energy upper stage propulsion. In contrast I hope there may someday be at least one low cost launch provider using a moderate energy upper stage propulsion system: SpaceX, using a fully recovered F9R. And there might be others!
Quote from: sdsds on 06/22/2014 02:37 amI have trouble imagining a low cost launch provider that uses a high energy upper stage. Delta, Atlas, Ariane, H-IIA; all are high cost. Further I doubt there is a low cost means of developing a launch system that includes high energy upper stage propulsion. In contrast I hope there may someday be at least one low cost launch provider using a moderate energy upper stage propulsion system: SpaceX, using a fully recovered F9R. And there might be others!So how does that argue in favour of LEO departure?
Quote from: sdsds on 06/22/2014 02:37 amthere may someday be at least one low cost launch provider using a moderate energy upper stage propulsion system: SpaceX, using a fully recovered F9R. And there might be others!So how does that argue in favour of LEO departure?
there may someday be at least one low cost launch provider using a moderate energy upper stage propulsion system: SpaceX, using a fully recovered F9R. And there might be others!
It's about the upper stage recovery of a "fully recovered F9R."
Quote from: RanulfC on 06/18/2014 09:17 pmIts also liquid at "room-temperature" and indefinatly storable as long as its "cooled" below room temperature. ..And compared to MMH/NTO peroxide has negligible flight history and track record in deep space. That includes engines and storage. Storability of hydrazine and ability to restart engines has been demonstrated after decades in space.It will take decades before any proposed peroxide system will gain a similar reliability record.
Its also liquid at "room-temperature" and indefinatly storable as long as its "cooled" below room temperature. ..
Peroxide has an extensive history, it's just that it was so long ago everybody's forgotten about it. In the 50s and early 60s, is was commonly used. Mercury's thrusters, for example, were peroxide-powered. Other applications included attitude control on the upper stages of the Scout, Titan I and Titan II, as well as the Syncom satellites (the first geosynch comsats).
Quote from: Proponent on 06/26/2014 07:40 pmPeroxide has an extensive history, it's just that it was so long ago everybody's forgotten about it. In the 50s and early 60s, is was commonly used. Mercury's thrusters, for example, were peroxide-powered. Other applications included attitude control on the upper stages of the Scout, Titan I and Titan II, as well as the Syncom satellites (the first geosynch comsats).Historically has peroxide always been pressure-fed? I know e.g. the V2 used peroxide for its gas generator, but I don't think the pump it drove pressurized the peroxide, only the main engine propellants.I've been rather assuming that the "winner" for a storable propellant EDS was going to be a pump-fed engine....
I'd be surprised if the monoprop peroxide thrusters were anything but pressure-fed.The largest application of peroxide has been in Britain's Gamma engine family, where it served as an oxidizer for kerosene. These engines had turbopumps driven, I believe, by peroxide decomposition. Among other applications, they powered the first two stages of Britain's Black Arrow launch vehicle.