1) Power supply - How long can Centaur's batteries last? That is the amount of time you have to launch the payload; a) Can you fit solar arrays to the Centaur?2) Rendezvous - How does the Centaur rendezvous with the mission module? (Accepting that Orion would need one for all by the shortest and least-ambitious missions);
3) TOI payloads - Centaur is fairly small as EDS options go. It is fine for launching a robotic interplanetary probe, but a crewed space probe would be as much as an order of magnitude greater. Would Centaur be able to push even just an Orion through TOI to any useful destination?
could you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS? Launch each of them seperately to rendevous up in orbit.
Quote from: Downix on 05/02/2010 09:49 pmcould you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS? Launch each of them seperately to rendevous up in orbit.I don't think that anyone has ever done a lateral rendezvous without the assistance of a crewed spacecraft equipped with an RMS. I'm sure it could be done, but whether the R&D would be cheaper than just building a larger (4- or 6-engine) Centaur-derived EDS is questionable.
Quote from: Ben the Space Brit on 05/02/2010 09:55 pmQuote from: Downix on 05/02/2010 09:49 pmcould you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS? Launch each of them seperately to rendevous up in orbit.I don't think that anyone has ever done a lateral rendezvous without the assistance of a crewed spacecraft equipped with an RMS. I'm sure it could be done, but whether the R&D would be cheaper than just building a larger (4- or 6-engine) Centaur-derived EDS is questionable.The issue with larger units is what will carry it up?
Quote from: Downix on 05/02/2010 09:49 pmcould you not design a framework which would enable 3 Centaur to hook onto a single unit, as the EDS? Launch each of them seperately to rendevous up in orbit.ESA was considering something similar, which is not surprising since its cryogenic upper stage is so small. The Mars DRM did something similar, which is not surprising given the large mass it had to put through TMI. But apart from complexity the drawback would be that you would still have to mitigate substantial boil-off issues.
I believe that you are talking about launching the Centaur as a payload, specifically as an EDS for a BEO mission.
1) Power supply - How long can Centaur's batteries last?
That is the amount of time you have to launch the payload;
2) Rendezvous - How does the Centaur rendezvous with the mission module? (Accepting that Orion would need one for all by the shortest and least-ambitious missions);
Quote from: Ben the Space Brit on 05/02/2010 09:10 pm3) TOI payloads - Centaur is fairly small as EDS options go. It is fine for launching a robotic interplanetary probe, but a crewed space probe would be as much as an order of magnitude greater. Would Centaur be able to push even just an Orion through TOI to any useful destination?If it's unmanned, without return propellant, yes. Otherwise Orion is too heavy
An option for boil-off is to house a shade around the mounting point of what you are mounting them to.
What if you did not do this in a single go, and you did staged EDS, you use one to push into a large eccentric orbit, then dump the first EDS. It then meets up with the second EDS, which has burned up more of its fuel to reach the item, and it pushes even more, to get things even more eccentric, where it then meets up with the last EDS, already en route. A way to get a *bit* more out of the system.
So the concept of operations would be the departure stage sending the payload (possibly even including crew) into a nominal "free return" lunar flyby orbit. The payload would have enough propellant to:a) in the nominal case, adjust its trajectory and perform an "insertion" burn (or burns) to reach its pre-positioned return propellant. (Or a pre-positioned return propulsion module.)
I hope lunar orbit, EML1 and EML2 would be reasonable crewed mission destinations for this architecture.
Is there a hope that dual-launch could be competitive with single-launch architectures for long duration robotic missions? Does it provide enough more mass to Earth-escape (compared to a single Atlas V 551 or Delta IV-H) to interest the science mission community? For example would it, in combination with Mars-orbit rendezvous, enable robotic Mars sample return?
This is an interesting idea. Sounds a bit like accelerated ACES or mini ACES.
Quote from: FinalFrontier on 05/02/2010 11:37 pmThis is an interesting idea. Sounds a bit like accelerated ACES or mini ACES. Yes, very much the same idea. The term "accelerated" here would mean, "using existing stages (or very minor modifications thereof) for the major propulsive maneuvers." Doing this would allow NASA to focus for the next few years on constructing payloads, principally a "deep space" Orion.
On the performance calculations: I'm getting about 17.5mT through TLI. You also have to take the mass of a docking mechanism and an extended duration mission kit into account. That might be enough to do L1/L2 insertion as well, even without the capacity of a Delta upper stage. I'd be uneasy with not having return propellant. A smaller capsule sounds like a better idea to me.