#31
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Pat Flannery wrote:
Is there any breakdown regarding how many of those are related to orbiter inspection, TPS repair, and SSME (I assume that the cargo version wouldn't use SSMEs, but rather expendable RS-68s for the sake of economy and system simplicity) postflight checkout and maintenance? Assuming that the shuttle goes away in 2010, there shouldn't be any objection to using the remaining inventory of SSMEs as expendables for a heavy lift vehicle. Leaving aside the six that have been lost in flight, there seem to be about 40 engines in the inventory (2005 through 2109), most of which have fewer than 10 flights. Even omitting the workhorse engines (i.e., 2012 with 22 flights), sufficient engines remain for several flights of a shuttle-derived heavy lifter. (I get my numbers from the available vehicle descriptions in press kits -- STS-108 omitted that info for some reason). Of course, the engines would be a mix of base, Block I, Block II, etc -- but if overall performance is an issue, either mix similar engines in the same cluster or design the flights around the nominal thrust levels for the least-capable engine (i.e., use 100% if the flight includes a base engine, 104% if the worst engine is a Block I). They're bought & paid for, and their only other use is as expensive paperweights in a few museums. It would actually be *more* expensive to replace them with RS-68s, since they'd have to be purchased (assuming that the SSMEs have been stored in reasonably controlled conditions). -- Reed Snellenberger GPG KeyID: 5A978843 rsnellenberger-at-houston.rr.com |
#32
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Rand Simberg wrote: So we don't care if we lose a billion-dollar payload? Or the price of relaunching? This notion of reliability being of no relevance for unmanned systems gets tiresome. Not to the same degree... for a manned launch you want around 99+% reliability if at all possible; for unmanned you can settle for 95%-97% (like most operational expendable rockets have) and realize that the loss of a couple in 100 launches will be more than offset by the money you save in not having to design and build to quite the high standards required to get to 99+%. It's where those last few percentage points start coming into play that you run into lots of added dollars- and extra equipment weight to overbuild things to make critical things redundant. Which cuts into your payload weight, and therefore ups your launch price per pound for large numbers of launches. Pat |
#33
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Ed Kyle wrote: (An aside - I once watched a hydrogen fire burning on Pad 39A after an abort. The flames licked right up the side of the orbiter (Discovery I think it was - with crew on board and ET fueled) discoloring the exterior. It burned for awhile and was more than a little uncomfortable to watch). Does anyone have more info on this incident? Pat |
#34
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Reed Snellenberger wrote: Leaving aside the six that have been lost in flight, there seem to be about 40 engines in the inventory (2005 through 2109), most of which have fewer than 10 flights. Even omitting the workhorse engines (i.e., 2012 with 22 flights), sufficient engines remain for several flights of a shuttle-derived heavy lifter. (I get my numbers from the available vehicle descriptions in press kits -- STS-108 omitted that info for some reason). Of course, the engines would be a mix of base, Block I, Block II, etc -- but if overall performance is an issue, either mix similar engines in the same cluster or design the flights around the nominal thrust levels for the least-capable engine (i.e., use 100% if the flight includes a base engine, 104% if the worst engine is a Block I). They're bought & paid for, and their only other use is as expensive paperweights in a few museums. It would actually be *more* expensive to replace them with RS-68s, since they'd have to be purchased (assuming that the SSMEs have been stored in reasonably controlled conditions). I was basing this on the idea that the Shuttle cargo carrier is kept around as an operational type of vehicle, with new build ETs and missions going into the 2020-2030 timeframe. If we actually intend to do a manned Mars mission we are going to need a heavy lift vehicle of some sort, and a Shuttle derived vehicle sounds like the quickest and simplest way to get it. pat |
#35
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On 2005-05-09, Scott Hedrick wrote:
"Henry Spencer" wrote in message ... Generally speaking, you cannot get a truly low-cost process by paring bits off a high-cost one. It ought to be a good way to use any leftover tanks and SRBs, rather than using them as museum pieces. There aren't likely to be many. NASA knows (roughly) how many flights it needs to make; they will, unless they explicitly plan to go over to a shuttle-derived vehicle, the production lines will close down. There may be a couple of tanks or SRBs "in reserve", in case of storage accidents, but not enough to justify a SDV development program. -- -Andrew Gray |
#36
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Pat Flannery wrote:
Looking at the LockMart CEV design with add-on living/docking area at the back reminds me of the way Hermes slowly grew into a reusable spaceplane with the nonreusable section hanging on the back, ruining the economics of the system- but at least in that case they had it going up on one Ariane booster; in this case it takes two launches to get to the same sort of configuration. The Lockheed design can fly earth orbital missions with just one launch. And, unlike the Russian Kliper design, the Lockheed CEV brings its earth orbit propulsion system home with it. That may or may not be a good thing... - Ed Kyle |
#37
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On Mon, 09 May 2005 11:53:20 -0700, Ed Kyle wrote:
...Both Delta IV and Atlas V have the same problems when it comes to CEV adaptation. Neither can handle a projected 20 ton CEV without core booster augmentation, (solid or liquid strap-on boosters). But NASA is either going to have to live with this or go shuttle-derived. I don't see the U.S. government (at least not the current one) coming up with the billions it will take to develop a new, more powerful core rocket just to launch CEV a few times a year. - Ed Kyle This is my second try at posting this. To me this brings to mind another question: Does the CEV need to be twenty tons? Soyuz was designed in the 60's and weighs seven metric tons. Phil |
#38
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On Mon, 09 May 2005 14:12:05 -0500, Pat Flannery wrote:
Given the present administration's desire for military space control, one can wonder if the great cross range requirement had a similar origin to that of the Shuttle's, with its delta wings- something the military wants for a military derivative of the CEV. Sorry, PAT, no conspiracy here. It was quite well known that the military wanted the crossrange for the "once-around" recon sat polar orbit launches from Vandenberg. This gave them a reason to buy into the shuttle, which got the shuttle needed funding. This also drove the large capacity of the payload bay. Pat -- Chuck Stewart "Anime-style catgirls: Threat? Menace? Or just studying algebra?" |
#39
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On Mon, 09 May 2005 15:00:31 -0500, Pat Flannery wrote:
Rand Simberg wrote: So we don't care if we lose a billion-dollar payload? Or the price of relaunching? This notion of reliability being of no relevance for unmanned systems gets tiresome. Not to the same degree... for a manned launch you want around 99+% reliability if at all possible; for unmanned you can settle for 95%-97% (like most operational expendable rockets have) and realize that the loss of a couple in 100 launches will be more than offset by the money you save in not having to design and build to quite the high standards required to get to 99+%. It's where those last few percentage points start coming into play that you run into lots of added dollars- and extra equipment weight to overbuild things to make critical things redundant. Which cuts into your payload weight, and therefore ups your launch price per pound for large numbers of launches. This only holds true if whoever is insuring these launches is doing so out of the goodness of their hearts, and they can afford to lose a couple hundred million dollars now and then. I think at one point in the mid-90's we were discussing this here, and it came up that over the decade previous to then, the space insurance industry had gone bankrupt. TWICE. I suspect that's what's eventually going to drive the development of reusable space transports and high flight rates. Phil |
#40
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On Mon, 09 May 2005 13:36:51 -0500, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in such a way as to indicate that: If these are using cryogenic propellants, you've got to get them all into LEO in fairly short order to prevent excessive propellant boil-off. Or subcool the propellants and insulate the tanks properly... |
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