Date: Sun, 2 May 93 06:17:40 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V16 #513 To: Space Digest Readers Precedence: bulk Space Digest Sun, 2 May 93 Volume 16 : Issue 513 Today's Topics: Combo Propulsion System!? Electrical Spacecraft via Magnetic field of earth? (2 msgs) Gamma Ray Bursters How energetic could they be? HST Servicing Mission Scheduled for 11 Days (2 msgs) LLNL Inflated space stations (was Deployable Space Dock..) moon image in weather sat image Mothership for Flybys and cutting costs.. Political banner in space Space Manuevering Tug (was HST servicing mission_) Teflon (Re: Long term Human Missions Vandalizing the sky Welcome to the Space Digest!! Please send your messages to "space@isu.isunet.edu", and (un)subscription requests of the form "Subscribe Space " to one of these addresses: listserv@uga (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle (THENET), or space-REQUEST@isu.isunet.edu (Internet). ---------------------------------------------------------------------- Date: Sat, 1 May 1993 23:01:44 GMT From: Henry Spencer Subject: Combo Propulsion System!? Newsgroups: sci.space In article <1993May1.043916.1@aurora.alaska.edu> nsmca@aurora.alaska.edu writes: >How hard or easy would it be to have a combo mission such as a solar sail on >the way out to the outer planets, but once in near to orbit to use more normal >means.. If you've got a good propulsion system that's not useful for deceleration, sure you can use chemical rockets for that part... but even just doing the deceleration chemically is a major headache. We're talking seriously high cruising velocities; taking the velocity down nearly to zero for a Pluto orbit isn't easy with chemical fuels. Incidentally, solar sails are not going to be suitable as the acceleration system for something like this. They don't go anywhere quickly. (I speak as head of mission planning for the Canadian Solar Sail Project, although that is more or less an honorary title right now because CSSP is dormant.) They can't fly a mission like this unless you start talking about very advanced systems that drop in very close to the Sun first. -- SVR4 resembles a high-speed collision | Henry Spencer @ U of Toronto Zoology between SVR3 and SunOS. - Dick Dunn | henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Sat, 1 May 1993 23:13:39 GMT From: Henry Spencer Subject: Electrical Spacecraft via Magnetic field of earth? Newsgroups: sci.space In article <1993May1.044441.1@aurora.alaska.edu> nsmca@aurora.alaska.edu writes: >Okay, the earth has a magnetic field ... >...if you put a object in the earth magnetic field, it produces electricty.. Well, it's not that simple -- you're in Earth's magnetic field, and you don't generate electricity -- but it can be done. >Now the question. Can you use electricity to power a space/low earth orbit >vehicle? and i fyou can, can you use the magnetic field of the earth to power >it?? The way you power things is with electricity, so the answer to the first question is definitely yes. (If you meant to say "propel" rather than "power", the answer is "sort of".) Yes, you can use interaction with the Earth's magnetic field to get electrical power, and there are potential applications for this. However, bear in mind that there is no free lunch. The energy isn't coming from nowhere. What such systems do is convert some of the energy of your orbital velocity into electrical energy. There are cases where this is a useful tradeoff. Using power obtained in this way for propulsion is useful only in special situations, however. What you *can* do is get your power by some other means, e.g. solar arrays, and run the interaction with the magnetic field in reverse, pumping energy *into* the orbit rather than taking energy out of it. If you want more information, trying looking up "electrodynamic propulsion", "tether applications", and "magsails". >Can the idea of a "dragless" satellite be used in part to create the >electrical field? No. A "dragless" satellite does not magically have no drag; it burns fuel constantly to fight drag, maintaining the exact orbit it would have *if* there was no drag. This is why there are quotes around "dragless". -- SVR4 resembles a high-speed collision | Henry Spencer @ U of Toronto Zoology between SVR3 and SunOS. - Dick Dunn | henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 2 May 1993 09:13:32 GMT From: Isaac Kuo Subject: Electrical Spacecraft via Magnetic field of earth? Newsgroups: sci.space In article <1993May1.044441.1@aurora.alaska.edu> nsmca@aurora.alaska.edu writes: >Okay, the earth has a magnetic field (unless someone missed something?) > >Okay if you put a object in the earth magnetic field, it produces electricty.. No, if you put a conductor in a changing magnetic field, it produces a voltage. The two ways you can do that with a permanent magnet is to move the magnet or move the conductor. The slow shifting of the Earth's magnetic field isn't really significant, especially when you consider how weak the Earth's magnetic field is to begin with. >Now the question. Can you use electricity to power a space/low earth orbit >vehicle? and i fyou can, can you use the magnetic field of the earth to power >it?? Well, it would require generating an incredibly large magnetic field to repel the Earth's magnetic field (as a magnet can repel another magnet). Of course, this force only works in one direction, and the magnetic field generated has to be unimaginably powerful. Magnetic repulsion drops off as 1/r^3, and the earth's magnetic field on the surface is already very weak. It would require some sort of unknown superconductor, and special nonmagnetic construction. And seriously hardenned electronics (optical computers, perhaps). And the physiological danger would be significant (due to the iron content in our blood, among other things). In other words, forget it. >Can the idea of a "dragless" satellite be used in part to create the electrical >field? > >After all the dragless satellite is (I might be wrong), a suspended between to >pilons, the the pilons compensate for drag.. I think I know what I want to say, >just not sure how to say it.. > >A dragless satellite sounds interestingly enough liek a generator. I missed out on the "dragless satellite" thread, but it sounds totally bogus, from this little bit. -- *Isaac Kuo (isaackuo@math.berkeley.edu) * ___ * * _____/_o_\_____ * Twinkle, twinkle, little .sig, *(==(/_______\)==) * Keep it less than 5 lines big. * \==\/ \/==/ ------------------------------ Date: 2 May 1993 01:51:04 -0500 From: Greg Howard Subject: Gamma Ray Bursters How energetic could they be? Newsgroups: sci.space,sci.astro In article <1993Apr26.200406.1@vax1.mankato.msus.edu> belgarath@vax1.mankato.msus.edu writes: >In article <1rgvjsINNbhq@senator-bedfellow.MIT.EDU>, jfc@athena.mit.edu (John F Carr) writes: >> >> >> How much energy does a burster put out? I know energy depends on >> distance, which is unknown. An answer of the form _X_ ergs per >> megaparsec^2 is OK. >> >different spheres: R=.25pc(Oort Cloud Radius), R=22.5pc(at the edge of the >galaxy), R=183.5pc or the edge of the galactic corona, and lastly at a >R=8800Mpc. > For a radius of .25 pc, we found an L around 10^32 erg/sec. Pretty >energetic for close by. for the coronal model, we found around 10^43 erg/sec. >And lastly, for the cosmological model an L=10^53. That's what you'd call >moderately energetic, I'd say. Any suggestions about what could put out that >much energy in one second? > -jeremy > > Supernovae put out 10^53 or 10^54 (i forget which, but it's only an order of magnitude...). Not in gamma rays, though. You'd hafta get all of that into gammas if they were at 9 Mpc, but if a decent fraction of the SN output was in gammas it could reasonably be extragalactic (but closer than 9 Mpc). I dunno SN theory so well, but I can't think of how to get many gammas out. Maybe I should look it up. Big radio galaxies can put out 10^46 erg/s *continually*. That's just in the radio... there are a lot of gammas around them, too, but "bursts"? Nah. Neither of these should be taken as explanations... just trying to show that those energies *are* produced by things we know about. greg ------------------------------ Date: 1 May 1993 14:44:02 -0400 From: Pat Subject: HST Servicing Mission Scheduled for 11 Days Newsgroups: sci.space,sci.space.shuttle,sci.astro In article henry@zoo.toronto.edu (Henry Spencer) writes: |In article <1rrgu7$9lp@access.digex.net> prb@access.digex.net (Pat) writes: |>>No, the thing is designed to be retrievable, in a pinch. Indeed, this |>>dictated a rather odd design for the solar arrays, since they had to be |>>retractable as well as extendable... |> |>Why not design the solar arrays to be detachable. if the shuttle is going |>to retunr the HST, what bother are some arrays... | |They can be detached in an emergency. But expensive hardware is not thrown |away casually (bearing in mind that nobody knew the design was defective). |If the deployment crew had found some nasty flaw -- the lid failing to open, |for example -- it would have been a bit embarrassing to have to throw the |solar arrays away to get the thing back in the payload bay. I guess it's kind of an aesthetics argument. I can see the solar arrays being expensive, and there could be contingencies where you would be throwing away brand new solar cells, but it seems so cheap compared toa shuttle mission, i wouldn't think they would bother. pat ------------------------------ Date: Sun, 2 May 1993 07:08:00 GMT From: David Ward Subject: HST Servicing Mission Scheduled for 11 Days Newsgroups: sci.space,sci.space.shuttle,sci.astro In article <1rrgu7$9lp@access.digex.net>, prb@access.digex.net (Pat) writes... >In article henry@zoo.toronto.edu (Henry Spencer) writes: >> >>No, the thing is designed to be retrievable, in a pinch. Indeed, this >>dictated a rather odd design for the solar arrays, since they had to be >>retractable as well as extendable, and may thus have indirectly contributed >>to the array-flapping problems. > > >Why not design the solar arrays to be detachable. if the shuttle is going >to retunr the HST, what bother are some arrays. just fit them with a quick release. > I didn't think the bi-stem design was used so much for the retrieval as for the ability to launch in a tight (size) STS envelope. This is my own guess, based on similar designs flown on other large STS-launched s/c (GRO, UARS). Also, there _might_ be some consideration given to mass requirements (bi-stems weight less than conventional S/A). Finally, the HST arrays _do_ have the ability to be detached--remember, they're going to be replaced with new arrays. However, as an ACS guy who's seen his branch management pull their collective hair out over HST, I would voice a hearty 'yea' to using conventional arrays over bi-stems, whenever possible. No half hertz flexible modes, no thermal snap, no problem. David W. @ GSFC ------------------------------ Date: Sat, 1 May 1993 20:36:23 GMT From: Josh Hopkins Subject: LLNL Inflated space stations (was Deployable Space Dock..) Newsgroups: sci.space Organization: University of Illinois at Urbana Lines: 20 Source-Info: Sender is really news@CRABAPPLE.SRV.CS.CMU.EDU Source-Info: Sender is really isu@VACATION.VENARI.CS.CMU.EDU kjenks@gothamcity.jsc.nasa.gov writes: >: In article <1993Apr30.000050.1@aurora.alaska.edu> nsmca@aurora.alaska.edu writes: >: >Why not build a inflatable space dock. [discussion of pros and cons deleted] >These are some of the technical difficulties which the LLNL proposal >for an inflatable space station dealt with to varying degrees of >success. Could someone give me the references to the LLNL proposal? I've been meaning to track it down in conjuntion with something I'm working on. It's not directly related to space stations, but I think many of the principles will carry over. -- Josh Hopkins jbh55289@uxa.cso.uiuc.edu "Find a way or make one." -attributed to Hannibal ------------------------------ Date: Sun, 2 May 1993 00:12:19 GMT From: "Mr. Krinkle" Subject: moon image in weather sat image Newsgroups: sci.astro,sci.space,sci.geo.meteorology,sci.geo.geology In article <1993Apr30.173625.10139@unocal.com> stgprao@st.unocal.COM (Richard Ottolini) writes: >In article turner@bigbang.astro.indiana.edu (George Wm Turner) writes: >> >> >>an image of the moon has been caught in a weather satellite images of the earth. >Near midsummer, you can see the relfection of the Sun in the ocean. Cool! >Also during solar eclise you can see the shadow of the sun move >across the clouds. ^^^^^^^^^^^^^^^^^ I think you mean Moon. (Sorry, I had to.) ; ) ------------------------------ Date: Sun, 2 May 1993 04:19:47 GMT From: Henry Spencer Subject: Mothership for Flybys and cutting costs.. Newsgroups: sci.space In article <1993May1.051312.1@aurora.alaska.edu> nsmca@aurora.alaska.edu writes: >... design a mother ship that has piggy backed probes for >different missions,namely different planets... Not useful unless you've got some truly wonderful propulsion system for the mother ship that can't be applied to the probes. Otherwise it's better to simply launch the probes independently. The outer planets are scattered widely across a two-dimensional solar system, and going to one is seldom helpful in going to the next one. Uranus is *not* on the way to Neptune. Don't judge interplanetary trajectories in general by what the Voyagers did: they exploited a lineup that occurs only every couple of centuries, and even so Voyager 2 took a rather indirect route to Neptune. >Also the mother ship would be powered (if not the Mars Mission) by a normal >propulsion, but also a solar sail ... Solar sails are pretty useless in the outer solar system. They're also very slow, unless you assume quite advanced versions. -- SVR4 resembles a high-speed collision | Henry Spencer @ U of Toronto Zoology between SVR3 and SunOS. - Dick Dunn | henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 1 May 1993 15:02:37 -0400 From: Pat Subject: Political banner in space Newsgroups: sci.space Well, you better not get the shuttle as your launch vehicle. and most ELV's have too far of a backlog for political messages. If during the campaign season, the candidates for president had launched one, right around now we'd be getting a launch for PEROT 92. and if they had used the shuttle, we'd be seeing launches for NIXON now more then ever. pat ------------------------------ Date: 1 May 1993 15:25:38 -0400 From: Pat Subject: Space Manuevering Tug (was HST servicing mission_) Newsgroups: sci.space In article jbh55289@uxa.cso.uiuc.edu (Josh Hopkins) writes: >prb@access.digex.net (Pat) writes: | |>Given that what i described for the HST seemed to be the SMT, and given |>the mass amrgins on the discovery mission is tight enough that spacewalking |>has to be carefully constrained..... No EDO pallets, no spare Suits, |>no extra MMU's. | |Has someone actually verified that mass is the predominant constraint on this |mission? You seem to be assuming it without giving supporting evidence. | Someone from NASA posted that there were very significant mass margins on the HST re-boost mission. A while back i had asked why not carry the EDO pallet up, and the answer was the mass margins were tight enough, they weren't even carrying extra suits. |>WHy not do this? | |> Quick Test Goldins philosophjy of faster cheaper, better. | |>Build a real fast Space TUg, to handle the re-boost of the HST using |>clean Cryo fuels, and get it ready before the HST mission. | |Pat, this would be slower, more expensive and worse. | |Slower: The shuttle mission is scheduled to go up in December. That's less |than eight months away. There is no way you could build new hardware, retrain |and reschedule the EVA's in that time. | Where's wingo when you need him:-) COme on. Knock that S**T off. YOu forget, that during skylab, they did overnight mission planning for the repair EVA's. Also during the Intelsat Mission, they did overnight WETF simulations. I somehow think they could train up a new EVA in 8 months. And as for building hardware, anything can be built if you want it bad enough. YOu forget, the BUS 1 is already built. all they'd ahve to do is soup it up, even test it on a delta mission. Don't get into this mode of negativism. besides, at the rate missions slip, the Discovery won't launch on this mission until March. that's almost a year. |More Expensive: Your proposal still requires the shuttle to do everything it |was going to do execpt fire the OMS. In addition, you've added significant |extra cost for a new piece of complex hardware. | Ah, but how much more expensive is the Second HST servicing mission. YOu forget, there is a bum FGS, the Solar array electronics, are getting hinky and there is still 8 months until the servicing mission. The time for the space walks are growing rapidly. THis was orignally planned out as 3 spacewalks, now they are at 5 EVA's with 3 reserve walks. If the SMT can avoid a second servicing mission that's $500 million saved. If the Weight savings, means they can sit on orbit for 30 Days. and handle any contingency problems, that's quite a savings. | |According to a GAO report on the OMV I have before me, there are |only two currently planned missions that could use such a vehicle -- HST and |AXAF. Since AXAF has since been scaled back and HST can rely on the shuttle, |there doesn't seem to be any need for your vehicle. Of course, there wasn't any need for the Saturn V after apollo too. as for the problems with the aperture door, I am sure they can work out some way to handle that. Maybe a Plug made from Frozen ice.? it'll keep out any contamination, yet sublime away after teh boost. pat ------------------------------ Date: 1 May 1993 15:06:54 -0400 From: Pat Subject: Teflon (Re: Long term Human Missions Newsgroups: sci.space,sci.space.shuttle,sci.astro In article <1rtghr$j9v@techbook.techbook.com> dant@techbook.techbook.com (Dan Tilque) writes: > |The material was useful for seals, but it had a major problem for, say |the linings of vessels: it wouldn't stick to metal. What the space |program did was to find a way to get it to stick. Thus we had no-stick |frypans on the market in the late '60s. Ejon Matejevic who was a full professor at Clarkson University, last I heard, developed the process for sticking Teflon to metals. I don't think it was a NASA project, cuz i heard he held the patent on it, and had made quite a bundle off it. Anyone from Clarkson know the Exact story. I never wanted to ask him myself. pat ------------------------------ Date: 1 May 1993 22:26:04 -0400 From: Pat Subject: Vandalizing the sky Newsgroups: sci.space In article 18084TM@msu.edu (Tom) writes: |On the other hand, I lived in OakBrook IL for a while, where zoning |laws prohibit billboards, as you mention above. I think it was a |fine law, despite it's contradictory basis. And I lived out there too. It was a nice sleepy farm valley until the Butler family decided to stick up all sorts of really tacky High RIse office buildings and ruin my view of the sky. I guess i should have sued somebody :-; pat ------------------------------ End of Space Digest Volume 16 : Issue 513 ------------------------------