...huh. I can't find any hard data to back it up, but there have been
claims that if you're careful, Dragon can be used as a crew taxi/return vehicle for an L2-staged lunar mission, or even an interplanetary mission. Of course, this plan requires that the EDS still be good after three days, and it loads extra requirements onto the mission module (no dual-docked Dragon missions to NEOs)...
Also, it turns out I may have overestimated the Dragon's mass. The LEO version is about 8 mT. That's probably the cargo version - the crew version might be heavier, and a BEO version would definitely be heavier - but if the BEO version could be kept down below 9 mT or so, a full F9US (filled at a depot) might be able to provide enough delta-V that the Dragon's onboard thrusters could plausibly finish the TEI from LLO, provided the lander has its own separate TLI/LOI stage and the Dragon stack doesn't have to push it anywhere. I don't like it, though, because the mass and propellant margins are a bit tight, and it requires the F9US to last through almost the entire mission.
I guess the technical possibility of using Dragon as a return vehicle for BEO missions without extra stage development depends on the loiter capability of the F9US, and on whether or not it supports on-orbit propellant transfer (it probably doesn't, which means this plan is DOA unless the feature is somehow easy to add). You also need a very capable mission module, and a means of getting
that to wherever you're going...
Skipjack wrote:Could it be that that Falcon 9 heavy version would be more suitable for this?
No. According to the
website, F9H is just a F9 with strapons, meaning the upperstage is the same. My calculations assumed a completely full upperstage, which means a depot is required (unless you want to daisy-chain multiple stages, which the stages probably aren't designed to support). A stretched stage might help, but it would have to be pretty big to work, since the propellant load required is much larger than the published payload for the F9H, and stretching increases the dry mass...
The Raptor-powered upperstage would be better delta-V-wise, but even the ACES architecture needs a depot, so I doubt very much that this one won't. In addition, the ACES stage is the culmination of 40 years of cryogenic stage design experience, and SpaceX has none whatsoever - I doubt SpaceX will be able to get the boiloff rate low enough for operation as a service module, never mind a depot...