Author Topic: SLS trades lean towards opening with four RS-25s on the core stage  (Read 143055 times)

Offline 93143

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We're going to have to get one of these things anyway because a second stage with a bunch of J-2Xs on it is too heavy to have optimal TLI performance

Have you seen the mass fraction for CPS?  Also, the US can go down to one J-2X.

Depending on the mission, that could still end up being too much thrust...

I don't really like the SLS-US either.  It's a battleship stage.  I guess my main problem is that I got enamoured of the ACES/WBC technology proposed for the JUS, and the relatively primitive conservative CPS and US concepts are comparing poorly.

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and we most definitely need CPS for Mars

Why?  Weren't you a huge fan of SEP a while back?  (I like advanced nuclear myself.)  Mars is 20 years in the future; we could be using Polywells by then.  Cryo storage?  Definitely.  CPS specifically?  I don't see it...

Offline Robotbeat

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Right, the CPS may have a bad mass fraction, but its low-boiloff technology is needed for chemical Mars missions.

SEP would work even if you went SEP for almost all the propulsion needs of the exploration stack, but I see a hybrid approach as much cheaper and realistic. For instance, using a SEP tug that has only a small fraction of the power of a full SEP propulsion stack to push the whole exploration stack to a Lagrange point or a high Earth orbit where it is met by a crew launched in Orion (or possibly some commercial crew-derived craft). Or even using SEP tugs to pre-place mission elements in Mars orbit or on its surface (obviously using EDL of some sort). Hybrid approach works well because it allows you to trade time for delta-v very deeply and because it's not necessarily on the "critical path" and is used only for pre-placing mission elements before any crew launches from Earth. Hybrid approach works best if you already have elements which can withstand long-duration spaceflight with very low-boiloff, like CPS.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline 93143

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Personally I like hydrogen as a VASIMR propellant.

I didn't say low-boiloff wasn't necessary.  In fact I specifically said it was.  But this does not imply that a stage identical to the proposed CPS is "most definitely" needed for Mars, which is what you said and what I was objecting to.  ACES, for instance, does low-boiloff too, with what appears to me to be a more sophisticated approach, and it can be sized for SLS.

I guess I'll let things evolve and see where this goes...
« Last Edit: 11/18/2011 08:47 pm by 93143 »

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