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« I'd Forgotten What A Boondoggle | Main | The Hypocrisy Of Congress »

The Incredible Shrinking SDLV

Well, the vehicle isn't shrinking--it's growing, actually. But it's SDLVness is definitely shrinking, as former astronaut Tom Jones points out:

Although it was plagued by development problems in the 1970s, the SSME has amassed more than a million seconds (more than eleven days) of reliable run time during the shuttle’s three-decade-long career. I’ve ridden twelve SSMEs to orbit on four shuttle flights, and they are smooth-running marvels of engineering. Fully reusable and burning highly efficient liquid hydrogen as fuel, each SSME is as finely tuned as a Swiss watch. But that complexity and efficiency means that building an SSME—even for just one throwaway use—is more labor-intensive than turning out an RS-68, which was designed for low cost and streamlined manufacturing. The RS-68, which also burns liquid hydrogen and oxygen, doesn’t yet have the track record of the SSME, but it has proven reliable in three Delta IV launches. For an expendable, non-astronaut-carrying Cargo Launch Vehicle, NASA’s engineers evidently decided that the SSME’s high efficiency and reliability were not worth the extra premium.

Of course, they've already decided that it's not worth it even for their astronaut-carrying Shaft..errr...Stick, either, since they've also replaced the SSME with the RS-68 on that vehicle. I'm wondering if this was a bait'n'switch on NASA's part--putting forth an SDLV architecture to assuage certain members of Congress (cough..Hutchison...cough...Nelson...cough) and Marshall long enough to get support to move forward, and then "discovering" that it might not be as cheap to keep all that expensive Shuttle infrastructure around after all.

If so, it's a good (or at least better) outcome than the original ESAS. The good news is that the use of all those RS-68s will provide more economies of scale (since the EELV program doesn't seem to be planning to use that many), reducing costs, at least in theory. The bad news is that we lose resiliency, with only a single liquid ascent engine for all of the human exploration activities. On the other hand, we never had that resiliency to begin with, since there is only one vehicle planned to carry out the missions. Fortunately, this will probably get fixed eventually, as private capabilities to deliver people and cargo to orbit develop (and likely long before NASA gets around to actually building its mondo grosso vehicle). There's a lot of taxpayer money to be wasted before that becomes recognized, though.

[Update a little after five eastern]

I should also note this article, via Clark Lindsey, that notes the other way in which the HLV is less SDLV, which is tied to the engine.

The previous thinking had been that they should go with ET barrel sections for the propellant tanks, because the tooling was in production for ETs, but they "discovered" (scare quotes for same reason as "conspiracy theory" above) that they could still manufacture Saturn-diameter tanks at Michoud, so they could go with the lower-performance, but also lower-cost RS-68s. So they're not using SSMEs, or Shuttle ET tooling. And there's nothing left of the Shuttle infrastructure except the RSRMs, which will be used to make new strap-on solids. In other words, it's no longer very Shuttle derived at all. Not that that's a bad thing...

[Update on Wednesday morning]

It's pointed out in comments that the Satay uses a J-2, not an RS-68. That's right. At least this week...

Posted by Rand Simberg at May 23, 2006 01:19 PM
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"I'm wondering if this was a bait'n'switch on NASA's part--putting forth an SDLV architecture to assuage certain members of Congress (cough..Hutchison...cough...Nelson...cough) and Marshall long enough to get support to move forward, and then "discovering" that it might not be as cheap to keep all that expensive Shuttle infrastructure around after all."

Sounds like a conspiracy theory to me. Besides, much the same contractors will still make money.

Posted by Mark R Whittington at May 23, 2006 02:07 PM

No conspiracy. Just bureaucratic response to Congressional incentives. And even if the same contractors benefit, they don't necessarily benefit in equal proportion, and Congresspeople (cough...cough) can't necessarily be counted to be smart enough to realize it.

Posted by Rand Simberg at May 23, 2006 02:18 PM

Oh, I think most politicians (Hutchison and Nelson especially) can be pretty intelligent when it comes to their political interests. They both know, at least since Columbia, that the shuttle's days are numbered. They both know that the shuttle workforce is aging and many will not be around much longer. They both know (because Griffin has openly said so) that the work force to operate the Vision will not be as large as the shuttle standing army. Finally, they both know that insofar as a pubicly funded space program goes, there really isn't any serious long term alternative to the Vision. Hence, I'm pretty usre that the bait and switch conspiracy does not exist. It was simply a matter of looking at an alternative that seemed to be a good idea at the time, finding at close examination that it wasn't, then trying a better alternative. Actually, it should be a comfort that it is happening now and not five or so years from now.

Posted by Mark R Whittington at May 23, 2006 02:54 PM

Mark, you may be right about the intelligence of the Congresscritters (though there was much discussion at the time to the contrary, by Dr. Griffin himself), but I continue to refuse to accept your claim that I postulate a conspiracy. I don't think that word means what you think it means.

Posted by Rand Simberg at May 23, 2006 02:58 PM

Umm, the stick doesn't use RS-68, but J-2X?

Posted by mz at May 23, 2006 09:47 PM

"Umm, the stick doesn't use RS-68, but J-2X?"

J-2X for the liquid propellent engine in the stick upper stage? That's what I thought too.

It occurs to me that since the HLV is going to use the J-2 engine for the third stage and use a 10m diameter stage for the liquid engines, isn't the HLV more of a Saturn V derived vehicle than a Shuttle derived one?

Posted by Brad at May 24, 2006 01:23 AM

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