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#221
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Magnus Redin wrote:
Hi! "Ed Kyle" writes: I like that idea, but it doesn't seem to be in the cards. CEV is being built primarily for lunar exploration, with ISS support as a secondary objective. NASA first talked about a 20 tonne CEV. Now Griffin is talking 30 tonnes. The most powerful single-stick EELV, Atlas V-402, can only boost 12-13 tonnes to low earth orbit. Why would lunar missions need a very large CEV when a small one can be docked with additional supporting components? Griffin seems to dis-favor Earth Orbit Rendezvous (EOR) mission architectures. In previous presentations, he has mentioned that EOR missions provide limited launch windows compared to other mission types. He said that because the earth-centered plane of the orbit must point to the lunar targeting position at trans-lunar injection time, launch opportunities will only be available every nine days from Cape Canaveral for a 28.5 degree redezvous orbit. In contrast, Lunar Orbit Rendezvous (LOR) and Lunar Surface Rendezvous (LSR) mission types offer two launch windows every day. My impression is that Griffin favors LSR, perhaps in concert with LOR for some elements. NASA has libraries full of such studies (of SDV). They've been funding studies for decades now ... Are those studies available for the public to read, learn from and criticize? Here is one place to start looking. "http://groups-beta.google.com/group/sci.space.history/msg/7d13b7cffc5465ba?hl=en" - Ed Kyle |
#222
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"Ed Kyle" wrote in message oups.com... Griffin seems to dis-favor Earth Orbit Rendezvous (EOR) mission architectures. In previous presentations, he has mentioned that EOR missions provide limited launch windows compared to other mission types. He said that because the earth-centered plane of the orbit must point to the lunar targeting position at trans-lunar injection time, launch opportunities will only be available every nine days from Cape Canaveral for a 28.5 degree redezvous orbit. In contrast, Lunar Orbit Rendezvous (LOR) and Lunar Surface Rendezvous (LSR) mission types offer two launch windows every day. My impression is that Griffin favors LSR, perhaps in concert with LOR for some elements. If you look at some of the PDF's who's links have been recently been posted by Rusty Barton to these newsgroups, you'll find that NASA has looked at LOR and LSR types of missions in the past and seemed to favor launch vehicles as big as, or even bigger, than Saturn V to launch these sorts of missions. Combine that information with the PDF's of Shuttle-C, NLS, and related launch vehicle studies and I think you'll get a very good idea how Griffin wants to get to the moon. Will this lead to a sustainable and scalable space program? I'd say no. At least it won't be any more sustainable and scalable than the shuttle program with it's half dozen or so launches per year. Jeff -- Remove icky phrase from email address to get a valid address. |
#223
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Jeff Findley wrote:
If you look at some of the PDF's who's links have been recently been posted by Rusty Barton to these newsgroups, you'll find that NASA has looked at LOR and LSR types of missions in the past and seemed to favor launch vehicles as big as, or even bigger, than Saturn V to launch these sorts of missions. Combine that information with the PDF's of Shuttle-C, NLS, and related launch vehicle studies and I think you'll get a very good idea how Griffin wants to get to the moon. Will this lead to a sustainable and scalable space program? I'd say no. At least it won't be any more sustainable and scalable than the shuttle program with it's half dozen or so launches per year. It is possible to see a future for an 80-100 tonne LEO lifter, but only doing government business. It only makes sense if it is considered as part of a program that leads to human Mars exploration. NASA's Mars Reference Mission, which Griffin contributed to, includes multiple launches of this type (of a rocket that at the time was called "Magnum") every two years. Yes, it will cost a bundle. But the argument seems to be that going to the Moon or Mars is going to cost a bundle no matter how you do it, and alternative clean sheet launch vehicle designs would cost more, given the relatively low launch rate, so NASA is saving us all money by reusing shuttle technology - or so the argument will go. But we have to go to Mars to realize the savings. :-) BTW, a close reading of these PDF and a review of Griffin's recent House subcommittee testimony provided something interesting. In his testimony, Griffin said that he was perfectly willing to consider EELV "as-is" for payloads under 20 tonnes, and that he expected EELV would probably be the cheapest option for such payloads, but he then talked about single-SRB designs that could loft 25-30 metric ton (tonne) payloads (presumably CEV). A look back at the 1995 Lockheed studies shows that the only designs capable of 30 tonnes used SSMEs, *not J-2S engines*, in the upper stage (SRB-J2S seems to max out at 25 tonnes) One option using a "Low Cost SSME" could do 29.5 tonnes (as much as the original space shuttle for maybe 1/3rd the price). A full-blown SSME-boosted upper stage on top of an ASRM (the advanced SRB design that was never completed) could orbit as much as 37 tonnes! OK, scale that back to 30 tonnes for an SRB instead of ASRM. That's 60 tonnes if you do two launches of these single stick rockets, using a total of two SRBs and two SSMEs (and two upper stages). Shuttle-C, which used two SRBs, two SSMEs, an ET, and two OMS pods, could only do 52 tonnes by comparison. Hmmmm. Where does this path lead? - Ed Kyle |
#224
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On 7 Jun 2005 18:34:47 -0700, "Ed Kyle" wrote:
OK, scale that back to 30 tonnes for an SRB instead of ASRM. Perhaps he's penciling-in using the Five Segment Booster instead of the standard RSRB? Brian |
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