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#1
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Running multiple HET in parallel?
Are there any known issues with running multiple HET
(Hall Effect Thruster) in parallel to get increased performance? Is it being already used somewhere? -- Sander +++ Out of cheese error +++ |
#2
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Sander Vesik wrote:
Are there any known issues with running multiple HET (Hall Effect Thruster) in parallel to get increased performance? Is it being already used somewhere? As long as you seperate them enough, sure. |
#3
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On Wed, 9 Feb 2005 07:46:49 +0000 (UTC)
Sander Vesik wrote: Are there any known issues with running multiple HET (Hall Effect Thruster) in parallel to get increased performance? Is it being already used somewhere? Just the energy cost, I think. It would be interesting to work out how much of a spacecraft you would have with a couple of submarine style fission reactors and as many ion or hall thrusters as you had power for. Given the lack of enthusiasm for this approach I can only assume that it doesn't deliver transit times short enough to be safe for humans. -- Michael Smith Network Applications www.netapps.com.au | +61 (0) 416 062 898 Web Hosting | Internet Services |
#4
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Michael Smith wrote:
It would be interesting to work out how much of a spacecraft you would have with a couple of submarine style fission reactors and as many ion or hall thrusters as you had power for. Given the lack of enthusiasm for this approach I can only assume that it doesn't deliver transit times short enough to be safe for humans. It would be interesting to know if there is currently any propulsion approach available that would allow significantly faster than Hohmann trips for humans to other planets/moons/major asteroids. (Our moon excepted, of course.) "Currently available" can be interpreted to mean "available by 2025 at a development + procurement cost of no more than $10G in 2004 dollars per year between now and then." Equally intresting would be to know about the technology for life support systems that would reasonably reliably sustain a half-dozen people for two or more years in space without help from Earth. |
#5
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In article .com,
Allen Thomson wrote: It would be interesting to know if there is currently any propulsion approach available that would allow significantly faster than Hohmann trips for humans to other planets/moons/major asteroids... "Currently available" can be interpreted to mean "available by 2025 at a development + procurement cost of no more than $10G in 2004 dollars per year between now and then." Yes: orbital assembly/fueling will let you do faster-than-Hohmann trips for small expeditions with chemical propulsion. You need an orbital fuel depot, and lots of fuel launches, but the former is fairly straightforward if you don't insist on using LH2, and the latter provides high flight rates for RLVs and a large competitive market for launchers of all sorts. Double yes: if you're willing to spend a bunch on R&D to reduce launch rates -- which is probably a bad deal, but is undeniably attractive to organizations that specialize in R&D -- solid-core nuclear rockets can considerably improve the picture, speeding things up further or permitting larger expeditions or both. Rover/NERVA solved most of the major technical problems of a first-cut version in the 60s, and demonstrated that a fast-paced program could improve the state of the art remarkably quickly in this area. You can start with NERVA derivatives, and pursue more ambitious designs in parallel with the first expeditions. The one big hassle is low-emissions test facilities, and it's one that should yield quickly to substantial amounts of money -- no breakthroughs are required. Liquid-core or nuclear-lightbulb is substantially better, and gas-core is much better, although they are longer-term options with significant development issues. Equally intresting would be to know about the technology for life support systems that would reasonably reliably sustain a half-dozen people for two or more years in space without help from Earth. Adequate water recycling -- the big issue -- has been demonstrated, on a modest scale. (Air is a minor side issue by comparison.) The simplest way to address the food loop is not to try, given that freeze-dried food weighs less than half a ton per man-year. Generally, much the simplest and most reliable way to tackle a lot of the smaller recycling/repair issues is brute force: more mass, and more fuel to push it, is cheaper than major engineering R&D. Of course, trying to sell that approach to R&D-oriented organizations is a bit of a challenge. "Anything which they do not wish to do is always lacking in technology. Whether single stage to orbit or Mars missions, the technology is never quite ready..." (Jim French) -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
#7
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Michael Smith wrote:
Correct me if I am wrong, but I can't see anybody supporting the development of nuclear rocket engines, given the political problems associated with simple RTGs. Why should this follow? RTGs are much more radioactive at launch than are reactors. The bigger problem with space reactors is development cost and lack of application. Paul |
#8
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Michael Smith wrote:
On Mon, 14 Feb 2005 05:18:28 GMT (Henry Spencer) wrote: You can start with NERVA derivatives, and pursue more ambitious designs in parallel with the first expeditions. The one big hassle is low-emissions test facilities, and it's one that should yield quickly to substantial amounts of money -- no breakthroughs are required. Liquid-core or nuclear-lightbulb is substantially better, and gas-core is much better, although they are longer-term options with significant development issues. Correct me if I am wrong, but I can't see anybody supporting the development of nuclear rocket engines, given the political problems associated with simple RTGs. Well, I support it. |
#9
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Michael Smith writes:
On Mon, 14 Feb 2005 05:18:28 GMT (Henry Spencer) wrote: You can start with NERVA derivatives, and pursue more ambitious designs in parallel with the first expeditions. The one big hassle is low-emissions test facilities, and it's one that should yield quickly to substantial amounts of money -- no breakthroughs are required. Liquid-core or nuclear-lightbulb is substantially better, and gas-core is much better, although they are longer-term options with significant development issues. Correct me if I am wrong, but I can't see anybody supporting the development of nuclear rocket engines, given the political problems associated with simple RTGs. A nuclear-electric thruster system, while inefficent, can at least be built from well understood components. I'm not following your logic. The "political problems associated with simple RTGs", were entirely due to A: some minor but non-negligible safety issues pertaining *only* to RTGs and not to any other space nuclear power system, and B: the fact that they used the N word. "Nuclear rocket" and "nuclear electric thruster system", both use the N word. If the political problems associated with simple RTGs will suffice to kill the one, they will just as surely suffice to kill the other. In fact, the political problems associated with simple RTGs, were overcome, and the RTGs flew. With that trail now blazed, I don't think nuclear systems are unthinkable. But if they are, they are *all* unthinkable. -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-718-0955 or 661-275-6795 * -58th Rule of Acquisition * |
#10
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Henry Spencer wrote: The simplest way to address the food loop is not to try, given that freeze-dried food weighs less than half a ton per man-year. Generally, much the simplest and most reliable way to tackle a lot of the smaller recycling/ repair issues is brute force: more mass, and more fuel to push it, is cheaper than major engineering R&D. Of course, trying to sell that approach to R&D-oriented organizations is a bit of a challenge. "Anything which they do not wish to do is always lacking in technology. Whether single stage to orbit or Mars missions, the technology is never quite ready..." (Jim French) I don't know enough about long-term nutrition and related matters to have an opinion, but note that the manned-Mars presentation at the recent Mars roadmap meeting contains the following assertions at slide 21: http://www.hq.nasa.gov/office/apio/p...an_studies.ppt Closing the life-support air and water loops with low expendables is a key leveraging technology for long duration human exploration missions Current food preservation technology is not capable of providing nutritionally viable food for the longer mission durations under study. Food production technologies under the environmental conditions of these missions is not developed to the point of being the primary source of food. Power requirements for both closed loop life support and food production can be significant, indicating that advanced life support and advanced power systems are closely coupled. [Boxed summary] Closing the air and water loops is essential to reduce the total mass of long duration missions to a reasonable level. Improvements in food storage technology or production technology are also needed to reduce overall mass and ensure crew health. |
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