Josh Hopkins has a thoughtful article over at The Space Review on the issues that must be addressed by proponents of propellant depots. I may have a response a little later, but I would note that Boeing has done a lot of work on the concept, and may have answers to some of the questions. In any event, we could have resolved them with a tiny fraction of the money that we just pissed away on Ares over the past four years.
[Update early afternoon]
In comments over there, Jon Goff makes one of the points that I would have had I gotten around to it (we’re getting ready to move, and writing SBIRs among other things, around here). It’s worth repeating:
2-Regarding launch costs: I think most depot researchers, like myself, would agree that if the cost for propellant delivery were truly likely to be in the $30-60kg range, that depots weren’t likely to make sense. However, is using delivery of cargo to a manned space station, where the cargo carriers themselves have to function as pressurized space station modules, really that realistic of a starting point for estimating the cost of propellant delivery to a likely unmanned depot? I know that that was probably the easiest way to do the analysis, since those numbers are available…but aren’t we setting up a strawman here? First you pick the obviously most expensive route (having the tankers be fully-functional prox-ops vehicles), and then pick one of the most expensive possible cases of such vehicles–vehicles designed to interface with a manned space station.
This is a typical tactic of opponents of an idea — to pick a worst case, and sort of imply that it’s a best one. It is not a realistic assumption, and was one of the flaws that jumped out at me at the time.
Another one is the concern about departure windows. Yes, launching from earth gives you more flexibility, but so what? If there are multiple opportunities per month from orbit (and there are, depending on how much you want to pay in delta vee for wider windows), then it doesn’t help you much to be able to launch more often from earth when your HLV architecture won’t be able to afford to launch more than a few times a year, even using the cost estimates of its most ardent proponents.
[Tuesday morning update]
Clark Lindsey has further thoughts.
[Bumped]
