#91
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Rand Simberg wrote: So? We end up with a lot of launches (assuming we can't get propellant from the moon). Big deal. Last time I had a house built, I don't recall demanding that it be delivered assembled on a giant truck. Assuming that your component parts go up on rockets that have around 95% reliability (which is around what most have, particularly the larger ones) and you've got to assemble something from say 20 or more parts...then you can be pretty sure of losing a part of it along the way....and that means building back-up parts for all the parts if you want to be fairly sure that you have all the components you need to assemble it, which won't be cheap. The cost of building a lunar base to extract propellant for the ship would be far more than any savings accrued from not bringing it up from Earth, at least if only a flight or two to Mars is intended. The Moon propellant extraction base option only makes sense if you intend to start doing a permanent Mars base, which is going to be one hell of a way down the road compared to what we are planning now. Pat |
#92
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"Jorge R. Frank" wrote in message
... "Neil Gerace" wrote in : " wrote in message ups.com... the DIV has to fly an odd trajectory (due to structural concerns) that means that there are points in the ascent when abort is *not* survivable. Is that bad? Seems to me that it happens to STS as well. No. That's due to not being able to terminate the SRBs safely, not due to trajectory as is the case with the D-IV. Well, I was only referring to the second part of the sentence: "there are points in the ascent when abort is *not* survivable." |
#93
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Andrew Gray wrote: this would be equivalent to saying that there's a dead-zone during takeoff where you can't try to do an emergency landing of the airliner, surely? Stop calling me Shirley. :-) The Ottopilot |
#94
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On Mon, 09 May 2005 21:35:49 -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 we actually intend to do a manned Mars mission we are going to need a heavy lift vehicle of some sort, Many believe this. That doesn't render it a fact. You are going to end up with a lot of launches if you try to do it with anything smaller than some of the proposed souped-up Delta IV heavy variants from the viewpoint of crew life support requirements alone. So? We end up with a lot of launches (assuming we can't get propellant from the moon). Big deal. Last time I had a house built, I don't recall demanding that it be delivered assembled on a giant truck. |
#95
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On Mon, 09 May 2005 21:47:38 -0500, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in such a way as to indicate that: Which cuts into your payload weight, and therefore ups your launch price per pound for large numbers of launches. That's an interesting theoretical argument, but in practice, what do you think that Thiokol would do differently in manufacturing a motor for an unmanned launch that they do for a manned one? The recovered SRB segments wouldn't have to meet the strict inspection requirements they now do. After Challenger, Thiokol is probably extremely paranoid about the recovered booster segments it fills and ships. I'll bet any scratches or small dents get the segment rejected, even though they shouldn't really compromise its structural integrity in any significant way. But they'd be far more likely to use something that isn't all bright and gleaming on a unmanned launch. If fact, for warm weather launches, you could use the old style pre-Challenger booster segments without any real problem. You could do all those things for manned launches as well. If you were sensible, anyway. |
#96
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On 2005-05-10, Pat Flannery wrote:
Assuming that your component parts go up on rockets that have around 95% reliability (which is around what most have, particularly the larger ones) and you've got to assemble something from say 20 or more parts...then you can be pretty sure of losing a part of it along the way....and that means building back-up parts for all the parts if you want to be fairly sure that you have all the components you need to assemble it, which won't be cheap. So, what you do, is you build one flight's worth of hardware in advance, so there's always a spare of each part "in stock" (this also protects you against manufacturing accidents, or the like)... which then gets used for the next flight, anyway. A little more sunk cost at the beginning, trivial increases for storage through the life of the program, and (possibly) some non-trivial savings on your final flight. -- -Andrew Gray |
#97
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Rand Simberg wrote: Not if a replacement part can go up on another cheap (something that heavy lift will never be at planned usage rates) ) launch. There's an old saying about eggs and baskets... I was concerned about the cost of the parts themselves- which could be more than the rocket that carries them. The big problem is needing replacements for ones that may get lost during launch. With our unmanned planetary missions we have many times used dual spacecraft in case one was lost for some reason. If you have to build a complete back-up modular Mars ship that will be expensive; the other concern is the launch window- can you get the replacement component for the lost one up and docked while the launch window is still open? Pat |
#98
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Rand Simberg wrote: Of course you should have backups for all the parts. It's not like you're only going to go once. To Mars? With all that entails? There'll be a very long time interval between the first manned flight for the prestige factor and the second one...for whatever reason it is done. It would be nutty to go to Mars at all if only a flight or two is intended. Remember the Bush administration suggested a manned flyby flight of Mars with no manned landing- which is about the nuttiest, most pointless thing I ever heard suggested in the field of spaceflight outside of the Soviet Voskhod test EVA by a dog. :-) Pat |
#99
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Andrew Gray wrote: So, what you do, is you build one flight's worth of hardware in advance, so there's always a spare of each part "in stock" (this also protects you against manufacturing accidents, or the like)... which then gets used for the next flight, anyway. A little more sunk cost at the beginning, trivial increases for storage through the life of the program, and (possibly) some non-trivial savings on your final flight. If we are talking Lunar flights, that makes sense. But if you think that the Apollo flights got truncated due to lack of public interest and the perceived high cost, wait till you see how fast manned Mars missions get ditched after the first one... especially considering the time factor involved for each flight. About the only thing one could do is build the component parts for the first mission in duplicate, so that you could be pretty sure that you could get at least one fully assembled ship in orbit for the first mission, and two if you are lucky. The journey to and from Mars will be about as exciting as the astronauts living on the ISS to the general public- and to tell you the truth, I sometimes forget there is even a crew on the ISS, or an ISS itself for that matter. Can you name the current ISS crew off of the top of your head? I sure can't. :-) Pat |
#100
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On Tue, 10 May 2005 18:49:56 GMT, h (Rand
Simberg) wrote: If it's going to be flags and footprints, as you imply, then we shouldn't do it at all. ....Gosh, then I guess scaling Everest shouldn't be done, either. Much less crossing the street. Coward. OM -- "No ******* ever won a war by dying for | http://www.io.com/~o_m his country. He won it by making the other | Sergeant-At-Arms poor dumb ******* die for his country." | Human O-Ring Society - General George S. Patton, Jr |
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