Subject: Space-tech Digest #137 Contents: P2-E, lunar colonies, ringworld bobbing, etc. (24 msgs) ------------------------------------------------------------ Date: Tue, 17 Nov 92 22:29 PST To: space-tech@cs.cmu.edu Subject: P2-E Development Costs From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) Kevin Ryan writes: > Wonderful work! Hope somebody picks up the ball and runs with it. > Any numbers on development costs? Find anyone who can help you run up > such costs? I don't have any hard numbers on development costs. I would like all the help I can get on this. I would advance the argument that the development of the overall system is likely to be no more expensive than that of the shuttle SRB. Major developments needed for SRB: - very large steel casings made of segments whose edges are pinned together - casting and inspection methods for huge propellant pours - nozzle and nozzle steering mechanisms - parachute systems - water recovery systems Development needed for P2-E - gas generator system - injector and combustion chamber - upper stage (existing engine with new tankage) I don't count tankage as a development item for the P2-E; the tanks are extremely simple and welding techniques are more akin to those widely used for high pressure natural gas pipelines than aerospace work. Does anyone have any figures on the overall development cost for the SRBs? Please don't post any figures without an an indication of which year's dollars we are talking about, and if at all possible give information on the actual development cost, not the projected cost given at the beginning of the program. -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ To: henry@zoo.toronto.edu Cc: space-tech@CS.CMU.EDU Subject: Re: Fuel-rich mixtures and specific impulse Date: Wed, 18 Nov 1992 11:29:31 EST From: John F Carr > No analytic shortcuts for all this are apparent. You have to grind through > it with computerized assistance and lots of tables of thermodynamic > properties of gases. It's something I have not done myself, so I can't > comment knowledgeably on difficulties. I did some such calculations when I took MIT's rocket propulsion course. I don't remember it being very hard, but we only worked with very simple cases (hydrogen + oxygen). I wouldn't want to try computing the exhaust velocity of a hydrocarbon burning engine without a computer and a good program. I remember the instructor telling us that many of the reaction rates and thermodynamic properties of intermediate products of hydrocarbon burning were unknown. ------------------------------ Date: 18 Nov 1992 11:38:04 -0500 (EST) From: "GORDON D. PUSCH" Subject: Re: P.S. to "Reactors banned in NEO?" To: avenger@wpi.WPI.EDU Cc: space-tech@cs.cmu.edu X-VMS-To: IN%"avenger@wpi.WPI.EDU" X-VMS-Cc: SPACE-TECH,PUSCHG Content-type: TEXT/PLAIN; CHARSET=US-ASCII Content-transfer-encoding: 7BIT Samuel J. Pullara writes: > I think he meant: How long does a positron last before it is annihilated > by an electron in the Van Allen Belts? > No, I meant what I said; I'd have to work it out to be sure, but my gut feel is that the Van-Allen electron density (and therefore the annihilation rate) is so small that the positron will get scattered into the loss-cone long before it annihilates --- that's why I said it would put an *UPPER* bound on the lifetime, which annihilation will reduce somewhat. Gordon D. Pusch ------------------------------ Date: Wed, 18 Nov 92 17:26:22 GMT From: amon@elegabalus.cs.qub.ac.uk To: space-tech@cs.cmu.edu Subject: Re: P2-E > I wasn't accusing them of being a knockoff of anyone. I was just noting > a similarity, in design philosophy more than anything else, to the work > of that guy whose name I _still_ can't remember (he was the one working > on water-launched boosters). > There were two actually. Starstruck launched a Dolphin to a couple(?) of miles. The people in that company were the predecessors to AMROC. The other never got further than paper. It was a proposal to the Navy (by the designer of the Volksrocket, built but not flown) called the Sea Dragon. ------------------------------ From: henry@zoo.toronto.edu Date: Wed, 18 Nov 92 13:00:22 EST Subject: Re: lunar vs. asteroidal industry To: space-tech@cs.cmu.edu > Some of the batteries used on unmanned spacecraft appear to have operating > temperature ranges much greater than that of fresh water - which might be > helpful given the day-night cycle on the moon. Hmm, I'm not sure what this would be referring to. Batteries are one of the two components (the other being fuel tanks and plumbing) that are least tolerant of temperature extremes. They are also inordinately heavy and have quite limited lives. Most batteries *contain* water in some form (although it's often in the form of a pretty thick chemical paste), as the medium for the electrolyte. A battery is basically just a fuel cell that also serves as the storage vessel for both the fuels and the reaction products. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ To: Bruce Dunn Cc: space-tech@cs.cmu.edu, gwh@lurnix.COM Subject: Re: P2-E Development Costs Date: Wed, 18 Nov 92 11:49:40 -0800 From: gwh@lurnix.COM I recall that the overall cost of the Shuttle program (Development, not operations) was roughly $50 billion dollars (and operations was about another $50 billion) in 1989 dollars through 1989 or 1990. I can't find the material that had those numbers right now, so I can't be sure or back it up. I _do_ remember that the SSME was the expensive component, and the Orbiter as a whole ate nearly all the money. The External Tank and the Solids were down around 10% of that figure total, so we're talking under $5 billion. Probably $3 billion for the solids including tooling up etc. Do remember that the cost per stage is sort of constant; upper stages cost more per pound to develop due to the extreme weight penalties as you get closer to orbital velocity.. so your upper stages may well cost as much per stage as the first (to develop). -george william herbert gwh@lurnix.com gwh@soda.berkeley.edu gwh@retro.com coming real soon ------------------------------ Date: Wed, 18 Nov 92 22:32:29 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@cs.cmu.edu Subject: Re: lunar vs. asteroidal mining >From: "Louis F. Adornato" >Subject: Re: lunar vs. asteroidal industry >Date: Wed, 18 Nov 92 7:18:45 CST >In-Reply-To: <9211170135.AA05912@cmr.ncsl.nist.gov>; from "John Roberts" at Nov 16, 92 8:35 pm >> >Storing excess generating capacity: >> >How about electrolyzing water, ... >> That might be a viable option. I think you'd want to use highly purified >> water that's not used for anything else - if fuel cells get contaminated, >> they don't work as well. >You don't run water through the fuel cells, you take water out. A >damaged fuel cell _might_ contaminate the water it produces (with >potassium), but since every manned American spaceflight since the >Gemini program produced drinking water through the fuel cells, I don't >think this is highly likely. I guess electrolyzing (or otherwise separating) the water to get hydrogen and oxygen would tend to remove the impurities. >> Some of the batteries used on unmanned spacecraft appear to have operating >> temperature ranges much greater than that of fresh water - which might be >> helpful given the day-night cycle on the moon. >I don't understand how this applies; I'm assuming that the fuel cells >and the tank farm will be inside habitable volume (to make maintenance >easier), so the operating temperature won't be a problem. Under ordinary operating conditions, I agree. But I've had a sufficient number of things I designed fall apart when conditions went out of the range I expected that I prefer to design conservatively when I can't be sure that the expected conditions will be maintained. We can presume that an inhabited lunar station will maintain an acceptable temperature range under normal conditions - but what if something unexpected happens? Are there scenarios in which the temperature control would fail (i.e. for a few days), but we would like the power system to resume operation later? (Perhaps the power system fails, but the inhabitants have sufficient stored oxygen to get by until they can fix it.) If the fuel cell contains water, and the water freezes, it could rupture the plumbing. I wouldn't say that potential problems will necessarily make the approach impractical - but precautionary measures should be taken. For instance, antifreeze could be kept on hand to pour into the fuel cell system in case of heater failure. Backup power systems should be available. If the station is to be abandoned for an extended period of time, perhaps the fuel cell plumbing could be heated and exposed to vacuum to drive out all the water. Here's a paragraph from "Lunar Science: a Post-Apollo View" from which one should be able to derive the equilibrium temperature of an unheated lunar base and the thermal conductivity of the lunar regolith: Measurements of conductivity indicate that the top layer is strongly insulating. There is an increase of about 47K in the top 83 cm. The top surface (2-3 cm) is a loosely packed porous layer. Surface temperatures are extreme. At the Apollo 17 site, the surface reaches a maximum of 384K (111C) and cools to 102K (-171C) at the end of the lunar night. The near-surface temperature is 216K (-57C). These temperatures are about 10K higher than those observed at the Apollo 15 site. The agreement with previous estimates based on terrestrial observations was very close. John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: Thu, 19 Nov 92 00:27:23 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@cs.cmu.edu Subject: Re: Fuel cells >Most batteries *contain* water in some form (although it's often in the >form of a pretty thick chemical paste), as the medium for the electrolyte. Since the hydrogen-oxygen fuel cells used in space are said to produce pure water, there can be problems if for some reason the temperature drops below 0C while there's water in the system. Sure you can put in safety factors to reduce the risk of this happening, but it's a nuisance, and that remains a potential weak point of the system. In comparison, fully charged lead-acid batteries can withstand extremely low temperatures - they contain water, but the acid lowers the freezing point. (Not that I'm advocating lead-acid for use in space or on the moon! :-) John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ From: henry@zoo.toronto.edu Date: Thu, 19 Nov 92 16:26:58 EST To: space-tech@cs.cmu.edu Subject: Re: lunar vs. asteroidal mining >... We can presume that >an inhabited lunar station will maintain an acceptable temperature range >under normal conditions - but what if something unexpected happens? The habitable volume is likely to be placed underground, for radiation shielding if nothing else. And the lunar-surface temperature variation drops *spectacularly* with depth. At a depth of 1m, there is no detectable day-night variation at all. Temperature there is somewhat site-dependent but otherwise constant. At the Apollo 15 site, it was 251-252K; at the Apollo 17 site, 255-256K (the ranges are between different points at the same site; there is *no* variation at any individual point, none whatsoever). There is a very slow increase of temperature with depth, again somewhat site-dependent, maybe 1-2K/m, although limited number of sites and limited depth explored would make one cautious about relying on this. [Data from Lunar Sourcebook.] Those temperatures are a bit cold, but the thermal conductivity of the regolith is very low, and any manned facility is going to have to worry much more about getting rid of waste heat. I would question, though, whether a regenerative-fuel-cell facility is going to be located indoors. Neither LH2 nor LOX is particularly wanted within a habitable space, since both are fire/explosion hazards (oxygen because it makes anything else burn ferociously; LOX accidents are nasty). In addition, by far the best insulator for cryogenic tanks is vacuum. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Thu, 19 Nov 92 22:51 PST To: space-tech@cs.cmu.edu Subject: Lunar Power Source From: Bruce_Dunn@mindlink.bc.ca (Bruce Dunn) Henry writes: > And the lunar-surface temperature variation > drops *spectacularly* with depth. At a depth of 1m, there is no > detectable day-night variation at all. So lunar regolith in a vacuum is a very good, and very cheap insulator. I propose the following power source: 1) Import to the moon three lightweight metal radiator/heat absorber panels with a circulating fluid which can withstand both lunar day and lunar night temperatures (probably some freon type chemical would do). 2) Find an outcropping of solid rock protruding slightly through the regolith. The rock will have a reasonably high thermal conductivity. Lay a panel on the rock, and cover it with a meter or so of regolith. Stick a sign over it labelled "heat source". 3) Repeat step 2) in another location, and label it "heat sink". 4) Lay the third panel anywhere on top of the regolith. Label it "heat absorber/radiator". Connect all three panels with fluid transfer lines and appropriate valving. 5) During the lunar day, circulate the fluid so that it transfers heat from the solar heated "absorber/radiator" to the rock under the "heat source" sign. During the lunar night, circulate the fluid so that it transfers heat from the "heat sink" to the "absorber/radiator" which radiates it away. 6) The net result of the above over a number of day night cycles is to create two masses of lunar rock, thermally coupled to heat exchangers, which differ in temperature by perhaps a couple of hundred degrees. Run a power generation system off the temperature difference. Carnot efficiency might be surprisingly good for the temperature difference because of the availability of a very cold heat sink. Availability will be essentially 100% - at the worst case the temperature difference available for a heat engine will be the difference between the two reservoirs. Better, during the day a heat engine can be run between the temperature of the solar absorber and the "heat sink" temperature, while at night a heat engine can be run between the temperature of the "heat source" and the temperature of the surface radiator. Does anyone have the analytical skills to run some calculation on this proposal to further examine feasibility? -- Bruce Dunn Vancouver, Canada Bruce_Dunn@mindlink.bc.ca ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Fri, 20 Nov 92 08:24:40 EST X-Mailer: Mail User's Shell (6.5 4/17/89) From: davidsen@crdos1.crd.ge.com To: <@crdos1.crd.ge.com,@crdgw1:mnr@gs80.sp.cs.cmu.edu> Subject: Re: lunar colonies on the cheap I'll throw out an interesting idea on combining two projects for a lot less than the sum of the individual costs... build the supercolider on the moon. Before you say that's obviously stupid, think of the reduced construction costs on the moon. Structural loads are far lower due to gravity, vacuum is readily available, cheap energy for some tasks is available half the time (mylar mirrors in parabolic configuration). I don't have any specs on the vacuum needed to run the experiment, but if the ambient vacuum would be enough then the design sure does get simple. I would shelve the space station for now; we don't have the technology to do the shielding in a sensible way. Some sort of self healing sheild is really needed before the station becomes practical. Anyway, there it is in all it's bizarre glory, now someone can tell me why it can't be done... -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) GE Corp R&D Center, Information Systems Operation, DSS group News admin for GE Corp R&D Cntr and Upstate NY UNIX User's Group systems "A pointed truth is an honest knife" -Gnoza, _Slow Lightning_ by Steve Popkes ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Fri, 20 Nov 92 09:08:51 EST X-Mailer: Mail User's Shell (6.5 4/17/89) From: davidsen@crdos1.crd.ge.com To: <@crdos1.crd.ge.com,@5D040103:mnr@gs80.sp.cs.cmu.edu> Subject: Re: Lunar "colony" reality check > >* A livable atmosphere is mostly nitrogen, not oxygen. > > Total biological ignorance. Humans can live quite well in a > 100% oxygen atmosphere. In fact, prior to the Shuttle, every > US spacecraft had a 100% oxygen atmosphere. Well, there were some significant problems with that atmosphere, mainly that any tiny heat source could become a total inferno in seconds. We learned this the hard way. Note that this is not nearly as much of a problem in orbit, because of the tendancy of flames to smother themselves due to lack of convection. But the moon has enough gravity to make a pure atmosphere dangerous. Also note that the absolute pressure was quite low, which is good for slowing leaks but which has not been evaluated for medical effects over months or years. Obviously there may not be any problem, but I would think a more earthlike atmosphere would be safer. ------------------------------ Date: Fri, 20 Nov 1992 10:33-EST From: Donald.Lindsay@GANDALF.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Re: Stirling engine >From: SMITH@EPVAX.MSFC.NASA.GOV (The Ice-9-man Cometh) >Does anyone remember >reading about a new sealed-cylinder, linear-alternator Stirling cycle >engine/generator a few months ago, and what the reference was? This sounds exactly like the tiny little chip refrigerator which was recently patented by Intel. Apparently they successfully eliminated the vibration by balancing the masses, and it just hums. One end is cold, one hot, and they put a fan on the hot end. You'll have to ask Intel Corp. Components Research for details. Don ------------------------------ Date: Thu, 19 Nov 1992 15:53-EST From: Marc.Ringuette@GS80.SP.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Ringworld stability On another list, jrk@information-systems.east-anglia.ac.uk (Richard Kennaway) writes: > It's well known that Niven screwed up his Ringworld, because > it isn't gravitationally stable, so he had to fix it with an active > stabilising mechanism in "Ringworld Engineers". (I have heard it can > be passively stabilised by having it oscillate parallel to its axis, ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > but I don't know if this is true.) Anybody know if this is the case? -- Marc Ringuette (mnr@cs.cmu.edu) ------------------------------ Date: Thu, 19 Nov 92 21:31:49 -0500 From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Re: Ringworld stability Marc Ringuette asked about "bobbing" stabilization of ringworlds. I did some simulations last year of a point mass moving in the gravitational field of a massive ring of finite radius but zero cross sectional area. A point mass starting near the origin with low velocity is quickly swept off center (the usual ringworld instability). However, if the point is given sufficient vertical velocity, it bobs up and down through the ring plane, and apparently never comes too close to the ring. The orbit is confined to a region around the z axis roughly in the shape of a hyperboloid of revolution. The displacement required is substantial; the orbit must go out of the ring plane a distance on the order of the ring radius. I didn't do a simulation of a light, rotating ring oscillating around a massive sun, but I imagine that if the rotation rate is sufficiently high the effect would be the same. Paul ------------------------------ Date: Fri, 20 Nov 92 00:40:05 EST From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. To: space-tech@cs.cmu.edu Subject: Re: Ringworld stability -However, if the point is given sufficient vertical velocity, -it bobs up and down through the ring plane... -The displacement required is substantial; the orbit must -go out of the ring plane a distance on the order of the ring radius. So I guess the Ringworld has seasons after all. :-) John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ From: ssi!lfa@uunet.UU.NET (Louis F. Adornato) Subject: Re: lunar vs. asteroidal mining To: uunet!zoo.toronto.edu!henry@uunet.UU.NET Date: Fri, 20 Nov 92 10:28:55 CST Cc: uunet!cs.cmu.edu!space-tech@uunet.UU.NET X-Mailer: ELM [version 2.3 PL11] John Roberts writes: >... We can presume that >an inhabited lunar station will maintain an acceptable temperature range >under normal conditions - but what if something unexpected happens? I sent most of the following directly to John and forgot to copy the list: When operating in microgravity, fuel cells need to be purged of excess water periodically (I thinks it's around every 6 hours max). Pre-shuttle crews did this by hand, on the shuttle it's part of the systems management software. The purge is done by shutting off one of the gas lines (the O2?), and increasing pressure in the other line. I don't think that they're vacuum dried, although I don't know why. When operating under lunar gravity, there's no reasson why the fuel cell couldn't use a gravity feed to keep itself clear of water (just one of the many reasons why a ground based installation would be cheaper than one onorbit). I beleive the cells normally generate enough waste heat to prevent freezing - I know that a recent dedesign of the Shuttle fuel cells removed the end cell heaters. Since there is always concern with any heater's control system failing while the heater is "on", this was generally considered a Good Thing. The shuttle uses independent, redundant fuel cells as it's only source of in-flight electrical power. There's no battery backup, and before anyone asks, the APU's provide _hydraulic_ power only. If I where going to bet my life on a power generating scheme (and the flight crews _do_), I'd go with this sort of system, rather than a battery backup. IMHO, the batteries (and the junk needed to isolate/connect them to the power busses) would _lower_ the overall system reliability. Henry Spencer writes: > I would question, though, whether a regenerative-fuel-cell facility is > going to be located indoors. Neither LH2 nor LOX is particularly wanted > within a habitable space, since both are fire/explosion hazards (oxygen > because it makes anything else burn ferociously; LOX accidents are nasty). > In addition, by far the best insulator for cryogenic tanks is vacuum. Hospitals have tanks of O2 all over the place. In fact, they have O2 lines running through the walls (at least, they do in the U.S. Can't speak for the socialized medicine of the second-and-a-half world to the north ;^). Is there any need to liquify either component? Going to cryo will mean tank stirrers, heaters, and vents. If cryo can't be avoided, I'd certainly recommend having the cryo tanks outside, but I'd still try to keep the rest of the system in the shirtsleeve environment. Doing maintenance with pressure gloves on is a bitch. Redarding power generation during the lunar day: Rather than using a mechanical system to convert solar heat to electical energy, why couldn't a thermocouple be used? Lou Adornato uunet!ssi!lfa | The secretary (and the rest of the company) Supercomputer Systems, Inc | have disavowed any knowledge of my actions. Eau Claire, WI | ** Space IS our future! ** ------------------------------ Date: Fri, 20 Nov 1992 13:29-EST From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: lunar colonies on the cheap Reply-To: davidsen@crdos1.crd.ge.com Sender: mnr@GS80.SP.CS.CMU.EDU I'll throw out an interesting idea on combining two projects for a lot less than the sum of the individual costs... build the supercolider on the moon. Before you say that's obviously stupid, think of the reduced construction costs on the moon. Structural loads are far lower due to gravity, vacuum is readily available, cheap energy for some tasks is available half the time (mylar mirrors in parabolic configuration). I don't have any specs on the vacuum needed to run the experiment, but if the ambient vacuum would be enough then the design sure does get simple. I would shelve the space station for now; we don't have the technology to do the shielding in a sensible way. Some sort of self healing sheild is really needed before the station becomes practical. Anyway, there it is in all it's bizarre glory, now someone can tell me why it can't be done... -- bill davidsen (davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen) GE Corp R&D Center, Information Systems Operation, DSS group News admin for GE Corp R&D Cntr and Upstate NY UNIX User's Group systems "A pointed truth is an honest knife" -Gnoza, _Slow Lightning_ by Steve Popkes ------------------------------ Date: Fri, 20 Nov 1992 13:30-EST From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: Lunar "colony" reality check Reply-To: davidsen@crdos1.crd.ge.com Sender: mnr@GS80.SP.CS.CMU.EDU > >* A livable atmosphere is mostly nitrogen, not oxygen. > > Total biological ignorance. Humans can live quite well in a > 100% oxygen atmosphere. In fact, prior to the Shuttle, every > US spacecraft had a 100% oxygen atmosphere. Well, there were some significant problems with that atmosphere, mainly that any tiny heat source could become a total inferno in seconds. We learned this the hard way. Note that this is not nearly as much of a problem in orbit, because of the tendancy of flames to smother themselves due to lack of convection. But the moon has enough gravity to make a pure atmosphere dangerous. Also note that the absolute pressure was quite low, which is good for slowing leaks but which has not been evaluated for medical effects over months or years. Obviously there may not be any problem, but I would think a more earthlike atmosphere would be safer. ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 20 Nov 92 14:02:25 EST To: space-tech@cs.cmu.edu Subject: Re: lunar vs. asteroidal mining Cc: space-tech@cs.cmu.edu >> I would question, though, whether a regenerative-fuel-cell facility is >> going to be located indoors. Neither LH2 nor LOX is particularly wanted >> within a habitable space... > >Hospitals have tanks of O2 all over the place. In fact, they have O2 lines >running through the walls (at least, they do in the U.S. Can't speak for >the socialized medicine of the second-and-a-half world to the north ;^). The socialized medicine of the northern wastes *invented* the treatment that Tsongas claimed he couldn't have gotten up here... Hospitals have O2 plumbing all over the place, yes, because they need it. They treat it with considerable respect. I believe they convert it from LOX to gaseous oxygen before they bring it inside; the tanks are always outside. The Saturn V program found that liquid oxygen was a much bigger handling hazard than liquid hydrogen, popular mythology notwithstanding. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ To: davidsen@crdos1.crd.ge.com Cc: space-tech@cs.cmu.edu Subject: Re: Lunar "colony" reality check Date: Fri, 20 Nov 1992 14:33:47 EST From: John F Carr > Well, there were some significant problems with that atmosphere, mainly > that any tiny heat source could become a total inferno in seconds. I thought the problem was using 1 atmosphere pure oxygen. Is pure oxygen at 3 PSI dangerous? Will plants grow in pure oxygen? Do they need nitrogen from the air? ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 20 Nov 92 15:42:44 EST To: space-tech@cs.cmu.edu Subject: Re: lunar vs. asteroidal mining Cc: space-tech@cs.cmu.edu >Is there any need to liquify either component? Going to cryo will mean >tank stirrers, heaters, and vents... Unfortunately, you probably need cryogenic storage. Even compressed, gases aren't very dense. For all the hassles, the NASA designs for regenerative fuel cells use cryo storage; anything else takes more mass hauled up. >Redarding power generation during the lunar day: >Rather than using a mechanical system to convert solar heat to electical >energy, why couldn't a thermocouple be used? Thermocouples are wretchedly inefficient. A turbogenerator is much the most efficient method currently known for converting heat to electricity. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 20 Nov 92 15:56:46 EST To: davidsen@crdos1.crd.ge.com Cc: space-tech@cs.cmu.edu Subject: Re: Lunar "colony" reality check >> ... In fact, prior to the Shuttle, every >> US spacecraft had a 100% oxygen atmosphere. > >Well, there were some significant problems with that atmosphere, mainly >that any tiny heat source could become a total inferno in seconds... 5psi of oxygen, which is what was used in orbit, is not significantly worse for fires than normal air. It's 15psi+ of oxygen, used for on-pad tests, that's the killer. Apollo kept its pure-oxygen in-space atmosphere even after the on-pad atmosphere was changed. (This is why, for example, there had to be an airlock module between Apollo and Soyuz for the Apollo-Soyuz mission.) Actually, the original statement isn't quite accurate. Skylab ran with a nitrogen-oxygen atmosphere, although I think it was lower in pressure and heavier on oxygen than normal air. >... Also note that the absolute pressure >was quite low, which is good for slowing leaks but which has not been >evaluated for medical effects over months or years. Obviously there may >not be any problem, but I would think a more earthlike atmosphere would >be safer. I believe the medical people do recommend normal air when practical, because of long-term unknowns (not just low pressure, but lingering suspicions of possible minor biological effects from nitrogen). You also probably want to air-cool your electronics, which is nearly impossible in low-pressure pure oxygen. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ From: henry@zoo.toronto.edu Date: Fri, 20 Nov 92 15:49:17 EST To: space-tech@cs.cmu.edu Subject: Re: Lunar "colony" reality check >Will plants grow in pure oxygen? Do they need nitrogen from the air? Most plants don't care whether there's nitrogen present or not; they are not equipped to use atmospheric nitrogen anyway (their nitrogen requirements have to be met from the soil). They do need some CO2, though. :-) Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Fri, 20 Nov 1992 16:45:08 -0500 (EST) From: PANITZ@ZWICKY.GSFC.NASA.GOV (Aliza R. Panitz - The Bug Lady) Subject: Plants and Nitrogen To: space-tech@cs.cmu.edu X-Vmsmail-To: SMTP%"space-tech@cs.cmu.edu" Someone asked: >Will plants grow in pure oxygen? Do they need nitrogen from the air? Henry Spencer (henry@zoo.toronto.edu) responded: !! Most plants don't care whether there's nitrogen present or not; they are !! not equipped to use atmospheric nitrogen anyway (their nitrogen requirements !! have to be met from the soil). Note, though, that on Earth there are a great many biological mechanisms for converting nitrogen to the forms that plants use. A significant lunar greenhouse would need a significant source of nitrogen fertilizer. (I'm no botanist, so don't look to me for numbers...) !! They do need some CO2, though. :-) Amazing how symbiosis works. :-) - Aliza (I don't speak for NASA, and NASA doesn't speak for me.) ------------------------------ End of Space-tech Digest #137 *******************