~Jon

We’re talking Atlas V here, right? For what it’s worth or even relevant, the current Atlas V takes a long time to get off the pad, so lowering the T/W ratio may be a problem. As it is, it takes 11 seconds to clear its launch tower, and, according to one source anyway, probably consumes over 50klb of propellant in its first 20 seconds to get to about 80 mph.

Taken. The Mars Society is more diverse than you imagine. The unifying factor is wanting to go to Mars, with at least some govt. facilitation and funding. Belief in a particular architecture is not a sine qua non of membership.

~Jon

As it is though, this is just a BOTE analysis showing that something like this *could* work. It would obviously need some actual trajectory modeling to verify the various remaining issues. It may turn out that there’s some reason it wouldn’t work, but at least on a preliminary basis, it appears feasible.

~Jon

Please stop making so much sense. Heaven forbid anybody figure out a way to close the gap and save money over Ares I.

In all seriousness, it’s a pretty sound approach. Ironically, it fulfills the flawed ESAS finding that EELV’s would need a bigger upper stage to pull off the crew launch mission. It also dispenses with the SRB’s which hurt your LOM numbers. My past experience with spreadsheets to do this kind of estimation has been iffy, but I got the impression that Atlas V would really benefit with a larger upper stage relative to the first stage. Due to the higher Isp for Stage 2, a bigger Centaur would result in a more optimal delta-V breakdown between the two stages.

If Ares I is dropped, perhaps NASA might also revisit the Orion specifications too, because sizing the Orion spacecraft for six crew makes no sense. If the lunar plan is for four crew than the Orion should also be sized for four crew, not six. Such a reduction in size would ease up much of the margin needed by the crew-launch vehicle and the cargo-launch Ares V (VI?).

In fact the only way the CEV specification makes sense is if the mass was deliberatly scaled-up by NASA to match the anticipated payload of Ares I. And it’s very clear much of the development costs of Ares V are piggybacked on the cost of Ares I. Hence the way NASA makes everything revolve around the desire for the heavy-lift Ares V which is a bass-ackwards method of coming up with a reasonable cost-effective architecture.

I don’t buy the NASA excuse that the six-man Orion capsule is needed for potential Mars misssions because I don’t see how a six man crew is a neccessity for such a hypothetical mission and much more importantly an Apollo moldline reentry vehicle is grossly inadequate for typical reentry speeds from a Mars mission. Reentry speeds from Mars are more like 14 km/s, much higher than the lunar reentry speeds of 11 km/s for which the Apollo shape was selected.

RE: Orbital refuelling of the Orion service module

An excellent idea, and one that had occured to me too as I fooled around with alternative lunar architecture concepts. And this made me consider another wild idea which I have yet to crunch the numbers on, what if the Altair’s ascent module (which is planned to use the same engine as the Orion) is also fuelled in orbit?

Looking at the Altair’s ascent module and it’s requirements and basic specifications made me consider another interesting possibility. Perhaps that ascent module could be so designed as to serve different jobs. Not only could it be used as the Altair ascent module, but also as a mission-module for the Orion (such as for NEO missions) and also as a reusable orbital tug (such as the Russian proposed Parom tug). In fact the configuration of the Parom tug might be a usefull jumping off point to design such a multi-purpose spacecraft. (I’d almost say such a spacecraft could serve as the Orion service module, but that is impractical for several reasons)