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Accumulate Fuel at Space Station?
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#12
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Accumulate Fuel at Space Station?
Markus Redeker writes:
(Gordon D. Pusch) writes: Rick Jones writes: [...] Only because certain electrical components within the tank were overloaded and caught on fire. Why were these electrical component _within_ the tank? The electrical components in question we 1.) The thermostat that sensed the tempertaure inside the supercritical oxygen tank, which necessarily had to be inside the tank to sense its internal temperature. It was this component that was overloaded; it was originally rated to run at 28 VDC, and when the tank heater design voltage was raised to 65 VDC to allow them to run directly off the launch-pad DC service, the tank thermostats were accidentally neglected when all the other components were upgraded. 2.) The circulation pump that circulated the supercritical oxygen through the tank heater when the thermostat indicated that the tank was too cold. it is possible that this latter Note that, while the ultimate cause of the accident was the thermostat contacts welding themselves closed, it was the _TEFLON ELECTRICAL INSULATION_ around the wiring to the above devices that initially caught fire. (In a supercritical oxygen environment, even relatively "inert" substances such as teflon burn quite cheerily!) Would they be necessary in a tank of a space station, too? Unlike the Apollo Service Module, the ISS does not appear to use "slushed" supercritical oxygen cooled by the excess heat capacity of liquid hydrogen, so it presumably does not need internal heaters nor stirring fans... -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
#13
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Accumulate Fuel at Space Station?
In article ,
wrote: I would like to know why we don't travel to Mars by first lifting many loads of fuel to the space station. The actual spaceship would be assembled in space, at the space station, from parts that are lifted there the same as the fuel is lifted, by conventional rockets... The idea is an old one -- early studies simply *assumed* that even a lunar expedition, never mind one to Mars, would have to be done that way -- and things will undoubtedly be done that way (using some space station, not necessarily the current one) eventually. The question is whether it's worth doing this for initial, relatively modest expeditions. The answer depends quite sensitively on the assumptions you make, like whether the current space station is used (it's in a poor orbit and is not equipped for the job), just how big your expedition is, and whether your goal is a one-shot program like what Apollo became, or something with an orderly growth path. There are two classical problems with this concept. First, it incurs some up-front investment which isn't repaid quickly, so it scores poorly by the standards of people who propose one-shot programs (some of whom don't realize that that is what they are proposing...). Second, it involves you immediately with the extremely expensive and inefficient bureaucracy that runs current US manned spaceflight, and some advocates of NASA Mars expeditions fantasize that their schemes can somehow avoid such involvement if only they avoid using the shuttle and the station. ...the thrust required might be only 1/20 of what it would be if launched from earth, so a small propulsive system will do the job. Yes and no. There are still efficiency losses if thrust is too low, so you don't want to make the propulsion system too small. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#14
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Accumulate Fuel at Space Station?
In article ,
wrote: OTOH, if the fuel was two components, say oxygen and hydrogen, then neither oxygen tanks not hydrogen tanks are explosive on their own. To keep them cold in space mainly requires sheilding from sunlight. True for oxygen, rather tricky for hydrogen (which has to be kept so much colder, and which can tolerate so much less heat leakage, that being able to store it without active refrigeration is questionable). Kerosene, of course, is no problem. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#15
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Accumulate Fuel at Space Station?
In article ,
nafod40 wrote: We could send up water, then just let solar array-powered electrolysis slowly do its magic to make the fuel. Two years for a bag of fuel? No problem, no rush. Such schemes have been looked at repeatedly, but unfortunately they tend to require inordinately large amounts of power. Water electrolysis needs roughly 10kW-hr/kg, and that is a *lot* of power by space standards. Electrolyzing 80t of water -- enough fuel for an Apollo-sized lunar mission, nowhere near enough for a Mars expedition -- in a year requires 90kW of continuous power. (Nearly double that if your electrolysis plant runs only when the station is in sunlight.) The full continuous design power of ISS when completed, assuming no further major Russian contributions, is under 80kW, and nearly half of that is required for station systems. That way no volatile components in the launch. You could freeze the water, and use it as part of the structure of the launch vehicle to reduce weight. Ice is not a good structural material, unfortunately. Alternate launch techniques such as rail guns? The payload would certainly tolerate the G's. So would most any liquid fuel. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#16
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Accumulate Fuel at Space Station?
In article ,
Gordon D. Pusch wrote: Note that, while the ultimate cause of the accident was the thermostat contacts welding themselves closed, it was the _TEFLON ELECTRICAL INSULATION_ around the wiring to the above devices that initially caught fire. (In a supercritical oxygen environment, even relatively "inert" substances such as teflon burn quite cheerily!) Normal Teflon is not too bad even in such an environment... but the Teflon in the Apollo 13 oxygen tank had been roasted severely when the tank heaters were earlier used (improperly) to try to empty the tank on the pad. The result was a crumbly material that was very flammable in supercritical oxygen. Unlike the Apollo Service Module, the ISS does not appear to use "slushed" supercritical oxygen cooled by the excess heat capacity of liquid hydrogen, so it presumably does not need internal heaters nor stirring fans... The conclusion is generally correct -- bulk storage of LOX for propulsion use would store it at or around its boiling point, and wouldn't need anything fancy inside the tank -- but the first part is messed up. Supercritical oxygen isn't slush, and the Apollo oxygen tank wasn't cooled by the hydrogen tank. "Supercritical" just means that storage pressure is high enough that the distinction between gas and liquid has vanished. This avoids the various complications of managing a tank which contains both liquid and gas in free fall, so supercritical storage is generally preferred when quantities are small and easy trouble-free operation without gravity is wanted. The price is that the high-pressure tanks are relatively heavy, so it's not practical for bulk storage. The S-IVB's LOX tank was cooled by heat leakage from the LH2 tank, but the Apollo SM oxygen tanks weren't. They just relied on good insulation, plus the fact that oxygen was constantly in use and hence a modest boiloff rate was perfectly acceptable. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#17
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Accumulate Fuel at Space Station?
In article , Markus Redeker wrote:
That said, ISS isn't in a good orbit to use as a stepping stone, Which orbit would you prefer? The best orbit for an orbital assembly base is equatorial, although that requires an equatorial launch site (not just near the equator, mind you, but very nearly on it -- even Kourou, at 5.2degN, is not really suitable). The big win is launch windows once per orbit instead of once or twice a day, and there are some lesser issues like lower radiation dose too. If it's a US project and you're not prepared to build a new launch base (or operate from floating platforms like Sea Launch), then a 28.5deg orbit like that originally planned for the space station is best. It doesn't have the unique advantages of an equatorial orbit, but it does maximize payload capacity for launches from the Cape. -- MOST launched 30 June; science observations running | Henry Spencer since Oct; first surprises seen; papers pending. | |
#18
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Accumulate Fuel at Space Station?
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#19
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Accumulate Fuel at Space Station?
Anthony Frost writes:
In message (Henry Spencer) wrote: In article , Markus Redeker wrote: That said, ISS isn't in a good orbit to use as a stepping stone, Which orbit would you prefer? The best orbit for an orbital assembly base is equatorial, The big win is launch windows once per orbit instead of once or twice a day, and there are some lesser issues like lower radiation dose too. If it's a US project and you're not prepared to build a new launch base (or operate from floating platforms like Sea Launch), then a 28.5deg orbit like that originally planned for the space station is best. Would there be any advantage in using a 23.5 degree orbit, arranged to be on the ecliptic, if your assembly is for interplanetary trips? The problem with any such inclined orbital plane is, it won't stay there. The perturbation exerted by the Earth's equatorial bulge will cause the plane of any orbit except 0 degrees and 90 degrees to precess. Hence, your "23.5 degree orbit" will only occasionally be well aligned with the ecliptic, and can be as far off alignment with the ecliptic as 47 degrees! I can't work out if being able to not have your assembled craft do a plane change is actually an advantage, let alone worth the payload and timing hit for delivering stuff to the assembly station. Plane changes are only a big deal if you are going from one orbit deep in a gravity well to another orbit deep in the _SAME_ gravity well. For translunar or "escape" transfers, the "plane change" can be handled during one of the mid-course corrections, after one is no longer deep in Earth's gravity well. -- Gordon D. Pusch perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;' |
#20
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Accumulate Fuel at Space Station?
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