[Note: Before I actually say something relevant, I want to give a little preface. If you don’t care about my ramblings and just want to read the technical stuff, skip the next two paragraphs.]
Ok, so I used to be a usenet junkie. It’s more or less what got me into this whole alt.space thing in the first place. Arguing with the Rand Simbergs, Ed Wrights, and others until I eventually figured things out enough that I didn’t sound like an idiot. However, after getting back from my mission, and particularly during the runup to the Iraq War, I noticed that the signal-to-noise ratio on usenet was getting even more heinous than it was previously (which is kind of impressive in a disturbing sort of way). Mostly it was Rand and a couple of liberventionists on the right versus a couple of annoying wingbats on the left, with me (a non-interventionist libertarian/classical liberal sort) generally pissing off both sides. So finally, around the time I got engaged to Tiffany, I decided to call it quits. I just got so annoyed at how everything kept degenerating into warmongering vs moonbatting, regardless of how technonerdy and innocent-like it started out. Since then I’ve managed to only post on a few rare occasions, even though I’d still lurk from time to time.
Apparently almost everyone else seemed to leave at around the same time. There were a few useful exceptions of course like Henry Spencer, Rand Simberg (when he actually deigned to give more than a one or two liner response, and when he wasn’t going off on non-related political tangents), and a couple of others. I use google news when I go to check in, and most of the current threads (all but one or two of them) on sci.space.policy are completely worthless, having little to do with actual space, and much to do with people wrapping tinfoil too tightly around their heads. In spite of all that however, every once in a while a good topic comes up, and yesterday I found myself posting a reply…
I won’t go int a play-by-play of who said what and how it got going in this direction, but Henry Spencer brought up an interesting thought. If you’re trying to develop a truly robust, cost effective and useful cis-lunar transportation infrastructure (ie one capable of dozens of trips to the moon in a year, not just a warmed over repeat of Apollo’s couple day jaunts for a few government employees), none of the systems in the architecture (CEV, CLV, HLV, EDS, or LSAM) really make a lot of sense. You really want to design a system that’s reusable, affordable, and can be tested incrementally. So here’s a few of my random thoughts on the topic, and on the discussion that Henry started.
In order to be reusable, a lunar lander pretty much needs to be single stage. None of this ascent module/descent module crap. We’re only talking about 4-5km/s of Delta-V. That isn’t really that much. Be a man, bite the bullet, take the initial payload hit, and go with a vehicle that has sufficient delta-V to land and return to lunar orbit or L-1. Any two-stage vehicle can’t readily be upgraded to being reusable without pretty much starting again from scratch. The delta-V’s involved in a lunar round trip aren’t that much more than what we hope to demonstrate with XA-1.5. With space rated engines used the whole way, and/or a more energetic propellant than Isopropanol, it should actually be pretty easy to pull off the mass ratios needed. In fact, being deeply involved with the design and development of a reusable VTVL lander, I really don’t see how you can design a vehicle that is safe enough and reliable enough for this mission without making it reusable. I would initially plan for refueling in-space, since we can’t really count on early ISRU for the first several flights. Any vehicle that can land and can be refueled in space by definition can be refueled on the lunar surface (or you’d at least have to try not to have it end up that way), so when there is ISRU available, that just allows you to start flying much heavier payloads per leg since you don’t need to carry the full load of return propellant all the way down. Also one of the ramifications of the 4-5km/s total delta-V is that particularly for hydrocarbon fuels, you’re going to be able to land a much bigger payload (with the return leg flying with no cargo) then you could for a round-trip payload like a passenger cabin.
Building a transfer vehicle that can’t deliver its payload all the way to a stable staging place (like L-1 or LUNO) is kind of pansy. Sure it worked for Apollo, but do you seriously mean that we need to build a brand new spiffy HLV just to launch a stage that can’t even put its payload all the way to lunar orbit? Having the CEV or LSAM do the actual capture into Lunar Orbit is a real cop-out. If you have tug that can actually take the payload to a staging place like L1 or LUNO, that allows you to reuse your landers. It also allows you to use a smaller tug more frequently by drylaunching the landers, and shipping over fuel and then the payload. The Apollo LEM only weighed something like 5 tons or so dry. A vehicle that can ship that much dry mass one way to L1 and then return empty to LEO can be much smaller than one that tries to fly a 40 ton behemoth part of the way there. That means a higher flight rate, and a more level demand for the earth-to-orbit transportation segment. It also means that even if you have to use an ELV or a recoverable (like what SpaceX is trying field) to launch the occasional big stuff, the “big stuff” can fit readily on a Falcon V or Falcon IX without any strapons. Which keeps the costs down.
I have a few more thoughts, but I’m out of time for tonight. If I get a chance tomorrow, I’ll post about propulsive braking vs aerocapture, to depot or not to depot (or better yet, when to depot), and do you really need a capsule for something like this?
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