|
Reader's Favorites
Media Casualties Mount Administration Split On Europe Invasion Administration In Crisis Over Burgeoning Quagmire Congress Concerned About Diversion From War On Japan Pot, Kettle On Line Two... Allies Seize Paris The Natural Gore Book Sales Tank, Supporters Claim Unfair Tactics Satan Files Lack Of Defamation Suit Why This Blog Bores People With Space Stuff A New Beginning My Hit Parade
Instapundit (Glenn Reynolds) Tim Blair James Lileks Bleats Virginia Postrel Kausfiles Winds Of Change (Joe Katzman) Little Green Footballs (Charles Johnson) Samizdata Eject Eject Eject (Bill Whittle) Space Alan Boyle (MSNBC) Space Politics (Jeff Foust) Space Transport News (Clark Lindsey) NASA Watch NASA Space Flight Hobby Space A Voyage To Arcturus (Jay Manifold) Dispatches From The Final Frontier (Michael Belfiore) Personal Spaceflight (Jeff Foust) Mars Blog The Flame Trench (Florida Today) Space Cynic Rocket Forge (Michael Mealing) COTS Watch (Michael Mealing) Curmudgeon's Corner (Mark Whittington) Selenian Boondocks Tales of the Heliosphere Out Of The Cradle Space For Commerce (Brian Dunbar) True Anomaly Kevin Parkin The Speculist (Phil Bowermaster) Spacecraft (Chris Hall) Space Pragmatism (Dan Schrimpsher) Eternal Golden Braid (Fred Kiesche) Carried Away (Dan Schmelzer) Laughing Wolf (C. Blake Powers) Chair Force Engineer (Air Force Procurement) Spacearium Saturn Follies JesusPhreaks (Scott Bell) Science
Nanobot (Howard Lovy) Lagniappe (Derek Lowe) Geek Press (Paul Hsieh) Gene Expression Carl Zimmer Redwood Dragon (Dave Trowbridge) Charles Murtaugh Turned Up To Eleven (Paul Orwin) Cowlix (Wes Cowley) Quark Soup (Dave Appell) Economics/Finance
Assymetrical Information (Jane Galt and Mindles H. Dreck) Marginal Revolution (Tyler Cowen et al) Man Without Qualities (Robert Musil) Knowledge Problem (Lynne Kiesling) Journoblogs The Ombudsgod Cut On The Bias (Susanna Cornett) Joanne Jacobs The Funny Pages
Cox & Forkum Day By Day Iowahawk Happy Fun Pundit Jim Treacher IMAO The Onion Amish Tech Support (Lawrence Simon) Scrapple Face (Scott Ott) Regular Reading
Quasipundit (Adragna & Vehrs) England's Sword (Iain Murray) Daily Pundit (Bill Quick) Pejman Pundit Daimnation! (Damian Penny) Aspara Girl Flit Z+ Blog (Andrew Zolli) Matt Welch Ken Layne The Kolkata Libertarian Midwest Conservative Journal Protein Wisdom (Jeff Goldstein et al) Dean's World (Dean Esmay) Yippee-Ki-Yay (Kevin McGehee) Vodka Pundit Richard Bennett Spleenville (Andrea Harris) Random Jottings (John Weidner) Natalie Solent On the Third Hand (Kathy Kinsley, Bellicose Woman) Patrick Ruffini Inappropriate Response (Moira Breen) Jerry Pournelle Other Worthy Weblogs
Ain't No Bad Dude (Brian Linse) Airstrip One A libertarian reads the papers Andrew Olmsted Anna Franco Review Ben Kepple's Daily Rant Bjorn Staerk Bitter Girl Catallaxy Files Dawson.com Dodgeblog Dropscan (Shiloh Bucher) End the War on Freedom Fevered Rants Fredrik Norman Heretical Ideas Ideas etc Insolvent Republic of Blogistan James Reuben Haney Libertarian Rant Matthew Edgar Mind over what matters Muslimpundit Page Fault Interrupt Photodude Privacy Digest Quare Rantburg Recovering Liberal Sand In The Gears(Anthony Woodlief) Sgt. Stryker The Blogs of War The Fly Bottle The Illuminated Donkey Unqualified Offerings What she really thinks Where HipHop & Libertarianism Meet Zem : blog Space Policy Links
Space Future The Space Review The Space Show Space Frontier Foundation Space Policy Digest BBS AWOL
USS Clueless (Steven Den Beste) Media Minder Unremitting Verse (Will Warren) World View (Brink Lindsay) The Last Page More Than Zero (Andrew Hofer) Pathetic Earthlings (Andrew Lloyd) Spaceship Summer (Derek Lyons) The New Space Age (Rob Wilson) Rocketman (Mark Oakley) Mazoo Site designed by Powered by Movable Type |
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 PMTrackBack URL for this entry:
http://www.transterrestrial.com/mt-diagnostics.cgi/5504 Listed below are links to weblogs that reference this post from Transterrestrial Musings.
Comments
"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 PMNo 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 PMOh, 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 PMMark, 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 PMUmm, 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? Post a comment |