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Moral Equivalent Of A Space Program
In article ,
Fred J. McCall wrote: Seems to me that it's expensive enough to get mass up there that we ought to plan on not bringing it back. And a space station, in particular, *wants* to be as heavy as possible -- that reduces the effect of air drag and hence the frequency of reboosts. (The average annual reboost fuel consumption is, to a good first approximation, unaffected. The reboosts take more fuel each, but they're less frequent.) -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#42
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Moral Equivalent Of A Space Program
On Wed, 15 Feb 2006 04:15:41 -0500, in a place far, far away, "Fred J.
McCall" made the phosphor on my monitor glow in such a way as to indicate that: ::No, I told you. Add up the development costs, and the ongoing :perational costs (including the costs of launching the cargo that is ::no longer launched by the manned vehicle, but can be by the Shuttle), ::divide by the flight rates, and you get an infrastructure that costs ::as much, or more than, the Shuttle. Even ignoring the amortization of ::the development costs, the marginal costs of the Shaft + CEV launch ::will be at least a couple hundred million, to deliver four crew ::instead of seven. Shuttle's marginal cost are about the same, to ::deliver a crew of seven, plus fifty thousand pounds of payload. : :Except you cheat the numbers because you don't include the development :and infrastructure development costs of the Shuttle in *that* number. : :That is not *cheating*. I told you, they're sunk. We have no choice ver whether or not to spend them, because that expenditure has :already taken place, and we don't have a time machine. When you're :making a decision to make a future investment in something that's stensibly to save you money, you *have to* include the investment as art of the total costs. Note that this is *NOT* the same question as whether it would be cheaper to get a pound to orbit than Shuttle. You're now asking if it makes free-market economic sense - and you haven't answered that question adequately, either. Either in the free market, or in a government expenditure, an economic decision has to be based on future costs, not sunk ones. There's an expression for your kind of thinking--"throwing good money after bad." |
#43
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Why The SM? (was Moral Equivalent Of A Space Program)
Rand Simberg wrote:
And the CaLV is already maxed out carrying the LSAM and EDS. It would be easier (and make more sense) to make that bigger, than the Satay. You would prefer NASA to make an even larger CaLV than it plans to? Who are you and what have you done with Rand Simberg? Will McLean |
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Why The SM? (was Moral Equivalent Of A Space Program)
On Wed, 15 Feb 2006 09:23:49 -0500, in a place far, far away, "Will
McLean" made the phosphor on my monitor glow in such a way as to indicate that: Rand Simberg wrote: And the CaLV is already maxed out carrying the LSAM and EDS. It would be easier (and make more sense) to make that bigger, than the Satay. You would prefer NASA to make an even larger CaLV than it plans to? No, I'd prefer that they dump ESAS entirely. But if you're going to build a heavy lifter, you might as well make it heavy (they're talking about a mondo grosso one for the Mars missions anyway). If the philosophy is to have a launcher dedicated to crew launches, and put everything else up on the heavy, then truly dedicate it to crew, and make the job easier on it. |
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Moral Equivalent Of A Space Program
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Moral Equivalent Of A Space Program
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#48
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Moral Equivalent Of A Space Program
In article , Gene Cash wrote:
And a space station, in particular, *wants* to be as heavy as possible... (The average annual reboost fuel consumption is, to a good first approximation, unaffected. The reboosts take more fuel each, but they're less frequent.) Hm. I think I'd consider fuel budget more important than frequency of reboosts. Note what I said: the fuel budget is *unaffected*. Loosely speaking, the requirement for reboost is that reboost thrust, averaged over the period between reboosts, equal the air-drag force averaged over the same period. Station frontal area affects fuel budget, but station mass does not. The one place where mass makes a difference to reboosts is that it slows down the effects of air drag. So if you reboost at the same frequency, your altitude varies over a narrower range, while if you let the altitude vary over the same range, reboosts are less frequent. I didn't think a reboost was that inconvenient, if you have to haul up the extra station mass *and* more fuel to keep it in orbit. Please read what I wrote: you *don't* need more fuel. And the mass in question is stuff that is already being hauled up there; the question is whether to go to added inconvenience to get rid of it. Reboosts actually are inconvenient, not least because they disrupt the microgravity environment that is one major reason to have a station. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#49
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Why The SM? (was Moral Equivalent Of A Space Program)
Ed Kyle wrote:
The choice of an Apollo-like ablative heat shield means that trying to protect propulsion module equipment, especially an engine bell, would add a lot of mass to the reentry module, and probably drive up overall spacecraft mass. When the reentry module gets heavier, parachute (and terminal retro) recovery systems get more complicated in a hurry too. If they used a lighter heat shield system (shuttle tiles?), it might be an easier problem to tackle. Of course you could go the Russian VA capsule route and put the retro system on the top of the capsule rather than on its base, and turn it into a jettisonable unit to decrease landing weight. You really want to save landing weight, jettison the whole heatshield after reentry like Soyuz does. Another problem with putting the retro/manuvering engines in the CEV CM itself would be noise when they are fired. Pat |
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Moral Equivalent Of A Space Program
"Will McLean" wrote in
ups.com: The CEV/CLV *could* do assembly, delivering modules instead of the unpressurized cargo module. They've chosen not to do that, choosing not to modify modules designed to launch on the shuttle. But there's nothing impossible about it. They'd have to modify the CLV as well; some of the modules will be beyond its lift capacity once the propulsion, guidance, and ISS docking/berthing systems are added in. Like you said, not fundamentally impossible, but costly in terms of both money and time. -- JRF Reply-to address spam-proofed - to reply by E-mail, check "Organization" (I am not assimilated) and think one step ahead of IBM. |
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