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Project Constellation Questions
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#22
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Project Constellation Questions
In article ,
Edward Wright wrote: Double that. It would take 5-6 EELV Heavy launches to perform a single lunar mission, It *could* take that many, but it could be done with less also. Lunar Gemini would have required two launches -- and the launchers they proposed were smaller than Delta IV Heavy. The only lunar mission that Lunar Gemini *definitely* could have performed with two launches was a free-return flyby -- not even lunar orbit, much less landing. When I break down typical lunar mission designs into launchable components, I find that a launcher in the 27-30 ton to LEO class would be about right. What do you consider a "typical" lunar mission, and what can't be disassembled down into components smaller than 27-30 tons? If we take the Apollo/Saturn design as nominal -- not because it is necessarily optimal, but just as a reference point with well-established mass numbers from actual hardware (as opposed to viewgraphs) -- the heaviest single lump was the S-IVB stage, dry, at about 17t. If you plan to fuel it in orbit, you probably want to go with some sort of modular tankage, which will increase the overall dry mass but reduce the mass of the base unit a little bit. (The performance hit from the extra dry mass can be recovered by draining one tank module at a time and jettisoning the empties immediately.) Given modular tanks for everything except the LM ascent stage (where dry mass is particularly critical), 15t is plenty. That's enough for the TLI-stage base unit, and for the LM with the ascent stage already fueled. The SM goes up with one not-quite-full tank module, and gets another added. The LM descent stage gets a tank module added. The TLI stage gets four LOX/LH2 tank modules, or a somewhat larger number for storables. And the CM goes up with the crew. You can go somewhat lower without significant changes to anything except the TLI stage. 10t ought to be straightforward. You can go *much* lower if you're willing to accept somewhat higher dry masses and get rather more aggressive about orbital assembly. But 10-15t is plenty for a scheme that does nothing but plug modules together, which we have already done and can certainly do again. The largest one I can think of is a human being, and they're more in the range of 0.1 tons. They're more like 0.3-0.5t by the time you add life support and safety equipment, although in a reusable launcher in particular, some of that might not count against payload mass. However, it's a *lot* of trouble to put together a lunar spacecraft from pieces of that size. Not impossible, but a big job for orbital assembly. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
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Project Constellation Questions
ed kyle wrote:
(Alex Terrell) wrote: A half descent moon program would require about 12 Delta IV Heavies (20-25 tons to LEO) every 2 years. (This would be in addition to USAF, commercial and ISS launches). Double that. It would take 5-6 EELV Heavy launches to perform a single lunar mission, This is not strictly true. I have at least two identified mission architectures which can fly one astronaut to the moon, land them, and return them to Earth on a single EELV payload (even Atlas V 551, not just Delta-IVH). One of them is an evolved Lunar Millennium, the other one is a different optimization but similar in some ways. The question of what good is a single astronaut, with a few days supplies and a Lunar Rover, is a valid question. But I presume we could land near a base and stay longer and operate longer as well. Throwing mass at problems is not always the right option. -george william herbert |
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Project Constellation Questions
(George William Herbert) wrote in message ...
ed kyle wrote: (Alex Terrell) wrote: A half descent moon program would require about 12 Delta IV Heavies (20-25 tons to LEO) every 2 years. (This would be in addition to USAF, commercial and ISS launches). Double that. It would take 5-6 EELV Heavy launches to perform a single lunar mission, This is not strictly true. I have at least two identified mission architectures which can fly one astronaut to the moon, land them, and return them to Earth on a single EELV payload (even Atlas V 551, not just Delta-IVH). One of them is an evolved Lunar Millennium, the other one is a different optimization but similar in some ways. Yes. You can send a single astronaut to the moon in a single EELV launch after spending about $1.5 to $2.0 billion on payload hardware. The question of what good is a single astronaut, with a few days supplies and a Lunar Rover, is a valid question. The same hardware can be adapted to unmanned one way flights. That means you can pre-position lots more payload for extended stays with enough equipment to do serious science. Ask this question, what good are a dozen astronauts spending a year on the moon? That's a valid question too! Imagine a moon program where there are two EELV launches per month - one with a single astronaut, one with a one way supply capsule. Imagine a stay time of twelve months. This is a way given this mission profile, a dozen scientists can be operating continuously on the moon - either together at a single site, moonbase fashion, or spread across the lunar landscape in a number of smaller more interesting sites. Rocket belts that burn the same propellant as the return engines could provide emergency long range transport between sites. With communications delay in the two second range its also possible to consider augmenting astronauts on the scene with rovers, instruments, etc., to increase their range of operations. A mix of automated systems tended by an astronaut on-site has a lot to recommend it. There are also business models like that of Lunacorp - where you send lunar rovers that can be driven by folks on the ground for a fee. You can also send and receive keepsakes from the lunar surface if you send even modest payloads back and forth. I don't think any of this can do the heavy lifting of making the program pay, but it can defer some costs at very little risk and involve the private sector. Then there is the Zubrin idea of using local resources to make propellants. THis could be done on the moon as well as mars. But on the moon we get oxygen from the soil. If this can be done, we can send larger manned vehicles on our small launchers and increase the amounts of equipment per dollar we send to the moon - increasing our presence there. But I presume we could land near a base and stay longer and operate longer as well. As I said, you could send 12 months supplies one way by adapting the manned harware to an unmanned supply capsule. So, in two launches you could have a long-term presence. A series of launches over the course of a year could in a few years build a substantial base. Throwing mass at problems is not always the right option. That's right. The central figure of merit is cost per kg-km/sec. Invest to lower this figure and what you can do in a given budget increases. -george william herbert William Mook |
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Project Constellation Questions
jeff findley wrote in message ...
Assuming NASA uses EELV at all. From last week's Space News, it appears Adm. Steigle has already decided he wants to develop a heavy lift vehicle, either Shuttle-C or an entirely new design. Given his position, would you really expect he propose anything other than a shuttle derived vehicle? He'll certainly lobby hard for such a vehicle, but that lobbying would be as much self preservation (and preservation of all of the people he manages) than anything else. Since he just came from DoD, I would have expected him to share DoD's fascination with EELV, rather than NASA's fascination with Shuttle and Saturn. If he's been captured by the bureaucracy after less than a month on the job, what's going to happen after a year... or a decade? |
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