Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Sat, 15 Dec 1990 02:40:49 -0500 (EST) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sat, 15 Dec 1990 02:40:16 -0500 (EST) Subject: SPACE Digest V12 #662 SPACE Digest Volume 12 : Issue 662 Today's Topics: Re: $$/pound of Freedom vs LLNL (was: ELV Support...) Re: Black Holes lest we forget Re: Black Holes Re: Black Holes Voyager Update - 11/30/90 Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription notices, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 8 Dec 90 18:31:05 GMT From: sumax!thebes!polari!crad@beaver.cs.washington.edu (Charles Radley) Subject: Re: $$/pound of Freedom vs LLNL (was: ELV Support...) - In response to:- Russ Cage Ford Powertrain Engineering Development Department Work: itivax.iti.org!cfctech!fmeed1!cage (CHATTY MAIL NOT ANSWERED HERE) Home: russ@m-net.ann-arbor.mi.us (All non-business mail) Member: HASA, "S" division. - >My original statement was correct as written, read it again. +But misleading. It even misled you: - Really Mr.Cage, you are coming on too strong. It is not my intention to mislead anyone, and I was not misled, simply making a different point to what you were. On the other hand, your numbers are misleading because they address only the pressurized hull and not the internal equipment nor the unpressurized regions. - >Thank you for adding more numbers, I note that the big volume of a >spinning station means it must accomodate a very substantial >pressure load compared with a non-spinning station, another weight >penalty. + +To summarize my numbers: + +Tension from pressurization: 190 klbs +Tension from rotation: 40 klbs + +This is a very small increment, ~20%. I've already shown +that the required mass of Kevlar to construct a 14.7 PSI +module is small, ~8000 lbs. For a 7.5 PSI module, it +would be about half that, even with the extra axial +tension. Circumferential stress would not change. - For the unpressurized portion, the centrifugal loads are much more significant. I have never seen a picture of LLNL showing solar arrays and unpressurized external palletts which are the main reason for Freedom's Truss. Where does LLNL attach its arrays and palletts ? Attaching them to the spinning part of a station means they will have to support their own centrifugal weight, the added support structure means the arrays will be much heavier per watt than the Freedom counterparts (assuming the same cells are used) which are pretty darn big. Any attachment at the spin axis itself will require re-introduction of a Freedom type truss extending along the spin axis. But that in turn would introduce pointing problems because the arrays must track the Sun. The mechnisms required would be big and beeffy compared to the Freedom alpha/beta joints which cost a fair chunk of change ! Allen says LLNL saves weight by getting rid of the Freedom type Truss, how then does it solve those problems ? I get the feeling, perhaps I am wrong..(?).., that LLNL avoids the solar array problem because it does not bother carrying much sceince equipment so does not need anything to power them with... BTW I am aware of LLNL's plan to try amorphous Si cells, but their fallback is to use conventional monocrystal a' la Freedom. - Regarding the circumferential stress..... The thickness of a pressure vessel wall increases in direct proportion to hull area, for a given material for a given percent stress margin. Therefore to save mass it is advantageous to make the volume as small as possible to minimise hull area. So an optimal design will always maximise the amount of equipment in every pressurized module, so the mass of the vessel itself ends up minor compared to the mass of equipment it contains. LLNL is not efficient, its huge volume is largely unused, and acts as a drag chute to boot. Scientific and support equipment mounted inside LLNL will of necessity be heavier than their counterparts in Freedom because they have to support their own weight and be supported by sturdy+heavy mountings. On a zero-g st+ation no such support structure is required for. LLNL puts multi+-level floors inside their vessel for mounting equipment and for personnel to walk on. Freedom has no need of these floors, so avoids that mass penalty. You get more science data per kilo on a zero-g station than a spinner. This is more significant than the hull weight, for example LLNL where the hull only weighs 8000 pounds out of a 40 ton total. Your 20% hull saving would not be a small increment, try telling that to the Space Station Freedom Weight Control Board....!!!! Even 20% mass reduction of the hull alone would be most welcome. You are thinking as a physcicist (my BS major) who concerns himself with orders of magnitudes. At the practical engineering level, 1% of a system is a big number. A 20% weight saving would be a compelling reason to make a station nonspinning. So far nobody has presented an equally compelling reason to make it spinning. If you consider the unpressurized portions and the internal equipment, the weight saving overall is greater than 20 % . That is if you bother to have internal equipment, LLNL does not seem interested in carrying much of that. - Haven't LLNL decided what their air pressure is ? The design cannot be considered credible without definition of such a fundamental parameter. The choice of cabin pressure has a major impact on EVA suits, personnel endurance, pressure vessel design etc. The Freedom program has done a lot of work trading off the relative merits of these parameters, and has a well defined baseline in that regard. Why do I expend my time worrying about LLNL, it sounds like they do not have a basic design defined. But I will continue in order to show that claims I am "not impartial" from Cage et al are unfounded. - +I am having serious doubts about your ability to impartially +analyze and critique concepts y+ou don't like. Part of being +scientific is checking your objections against reality and +'fessing up when they don't hold water. - I think you do not underrstand the points I am trying to make. Partly a problem with this electronic medium. There are some good ideas in the LLNL proposal, such as using Kevlar to save some weight. But spinning the station and being such a large volume are bad ideas. Your numbers do not show otherwise. - >LLNL at a higher altitude will have a more severe radiation >environment than Freedom. + +It was my impression that LLNL specified a LOWER orbit. My +archives are at home. Allen? - Somebody previously stated LLNL orbits at a higher altitude to compensate for its higher drag to weight ratio, but Allen says otherwise.... - >Also, the shielding capability of LLNL's non-metallic structure is >much less than Freedoms aluminum modules. + +1.) Soft X rays are stopped b+y almost anything. Fred offers + little superiority of protection. - True enough - you see I accept facts. But that ain't the biggie. - +2.) Charged particled are stopped by Earth's magnetic field. - Untrue have you ever heard of the South Atlantic Anomaly (SAA) ? That is the dominant source of radiation for a LEO spacecraft. For those who do not know, the SAA is akin to a "hole" in the Earth's magnetic field. - + Orbiting lower would give superior protection against + protons, which LLNL does if memory serves. (Allen?) - True. But orbiting lower increases drag which is already high for LLNL. Allen says that is accounted for. And a spinner spends less time broadside than the gravity-gradient mode. But it increases risks of decay due to failure of a resupply flight. I am really concerned that LLNL has not properly addressed ACRV, Resupply and Crew Rotation spacecraft. These are big ticket items, whose costs do not seem properly recognized by the LLNL plan. And they are also mission critical. The only proposal I have seen from Allen was to use Soyuz, but Wales Larrison has shown that Soyuz is not capable of the roles required for LLNL logistics. - +3.) Cosmic rays are less dangerous than their secondary + particles. F+red's aluminum structure would be MORE + DANGEROUS than LLNL's lighter pressure hull. - Fair enough. But this is a small contribution to the LEO radiation environment. - +PS: Charles, your news-posting software is faulty; it does not +insert attributions or maintain the References: line properly. +Please have it fixed. - I do not use online Unix reply program since it costs me $$$$ to stay online. My offline IBM-PC cannot do what you want. When I log back into Unix sometimes the message I am replying to has expired so I attach to another in the same string. I will desist if it causes confusion. - +Also, if you could keep your line +length down to 70 characters, it would be appreciated. - OK, wilco. -- - . :wq ------------------------------ Date: 8 Dec 90 17:18:13 GMT From: cs.utexas.edu!news-server.csri.toronto.edu!qucdn!gilla@tut.cis.ohio-state.edu (Arnold G. Gill) Subject: Re: Black Holes In article <2389@mentor.cc.purdue.edu>, xxc@mentor.cc.purdue.edu (Raymond Seibert) says: > >According to what I know about the current theory >about them, they begin as regular supergiant stars, then collapse in on >themselves. Here is what I don't understand, it then procedes to turn >inside out, leaving a void in the center. Now let me tell my version of the >story. It keeps collapsing until it can collapse no more -- possibly forming >a donut(sp?) shape?. It can still behave as the above theory's black hole >does, but matter keeps sticking onto the top of the existing matter. Now >according to this theory, the black hole should at some point consume enough >matter to make it unstable. This in turn would cause all the compressed >matter to be spewed out in a tremendous explosion. Of course I have no >mathematics to back it up, but I think it is conceptually possible. Believe >me; its better than that 4D crap that they try to pull on us. Except that the `4D crap' is correct while your version isn't. Actually, the way you have described things isn't too far off from a supernova explosion, if you would substitute neutron star for black hole. The core of the star collapses until the pressures are so great that it `bounces'. This is the shock wave that starts the explosion. However, if the collapse goes so far as a black hole, well, then there will be no more expansion, as any additional matter will just fall into the black hole, though giving off a lot or X-ray/gamma ray radiation. You must remember that a supernova explosion is an extremely quick, dynamic process, with times under 2 hours -- some would even say minutes. There isn't much time for a stable situation to arise. Also, the doughnut shape you mention would be the rough shape of the singularity of the rotating black hole, not of the black hole itself. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- | Arnold Gill | - If I hadn't wanted it heard, | | Queen's University at Kingston | I wouldn't have said it. | | InterNet: gilla@qucdn.queensu.ca | - Astrophysician in training | -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- ------------------------------ Date: 7 Dec 90 17:08:51 GMT From: mnetor!utzoo!henry@uunet.uu.net (Henry Spencer) Subject: lest we forget On this day 18 years ago, the last ship sailed for the Moon. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 9 Dec 90 06:54:39 GMT From: cs.yale.edu!yarvin-norman@CS.YALE.EDU (Norman Yarvin) Subject: Re: Black Holes henry@zoo.toronto.edu (Henry Spencer) writes: >Maybe, but you won't like it. :-) The "4D crap" is, near as anybody can >tell, the best description of the situation available. However, you don't >really need it for an intuitive understanding. You get a black hole when >gravitational collapse of the core of a massive star goes far enough that >the core's escape velocity exceeds the speed of light. Presto, a black >hole: anything goes in, nothing comes out. I have heard this explanation many times, and find it hard to understand using a simple-minded or 'intuitive' view of relativity. Granted that if the star's escape velocity exceeds the speed of light, then a photon starting from the star's surface can't make it out. But it seems to me that if one can propel some piece of matter any distance away from the black hole, then one can lift fuel up to that distance; using this fuel one can lift the next piece of matter even farther away from the center; and thus by degrees something could escape entirely from the black hole. I grant that it seems a bit improbable for inanimate matter to organize itself so well, but black holes have always been portrayed as completely escape-proof. Now, the other half of what I have heard about black holes refers to them having an 'event horizon', where 'the space-time structure curls back upon itself' or something similar. It would seem to me that something of this nature is really necessary to explain black holes, and that quasi-Newtonian explanations just can't cut it. Corrections, clarifications, or even agreement gladly accepted. -- Norman Yarvin yarvin-norman@cs.yale.edu "...and being driven slowly and quietly into the kind of terminal craziness that comes with finally understanding that the one thing you want is not there..." - Hunter S. Thompson ------------------------------ Date: 9 Dec 90 01:33:32 GMT From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utzoo!henry@apple.com (Henry Spencer) Subject: Re: Black Holes In article <2389@mentor.cc.purdue.edu> xxc@mentor.cc.purdue.edu (Raymond Seibert) writes: >...but I think it is conceptually possible. Believe >me; its better than that 4D crap that they try to pull on us. Maybe Henry >can help me out on this one. Maybe, but you won't like it. :-) The "4D crap" is, near as anybody can tell, the best description of the situation available. However, you don't really need it for an intuitive understanding. You get a black hole when gravitational collapse of the core of a massive star goes far enough that the core's escape velocity exceeds the speed of light. Presto, a black hole: anything goes in, nothing comes out. Matter near the core, falling inwards at a good fraction of the speed of light, is greatly heated and compressed as it does, and the combination of that heating and nuclear reactions caused by it releases ample energy to blow off the outer layers of the star. Complications like spin can mess things up badly, to the point where we probably need a more sophisticated theory than General Relativity to explain all of it, and even in simpler situations you can't predict the details reliably without getting into the math, but the basic notion is not hard to grasp. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 11 Dec 90 03:57:34 GMT From: usc!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov!baalke@apple.com (Ron Baalke) Subject: Voyager Update - 11/30/90 VOYAGER STATUS REPORT November 30, 1990 Voyager 1 The Voyager 1 spacecraft collected routine UVS (Ultraviolet Spectrometer) data from sources HD193322 and HD206165. On November 20 a frame of PWS (Plasma Wave) data was recorded on the DTR (Digital Tape Recorder) for future playback. Round trip light time to Voyager 1 is 12 hours, 12 minutes. Voyager 2 The Voyager 2 spacecraft colleted routined UVS data from sources Feige 7 and Mark 335. Glimpses into the data indicate the instrument is doing well. On November 20 a frame of PWS data was recorded on the DTR for future playback. Round trip light time to Voyager 2 is 9 hours, 28 minutes. DTR Maintenance and PMPCAL (calibration of the Plasma, Magnetometer and Low Energy Charged Particles instruments) sequences were executed on November 20. Approximately two hours of the six hour DTR Maintenance activity and thirty minutes of the three and one-half hour PMPCAL activity wprior to the scheduled end of the Goldstone 70 meter track. There was station coverage for only the first few minutes of the calibration, but the limited coverage indicated the PMPCAL was going well. CONSUMABLE STATUS AS OF 11/30/90 P R O P E L L A N T S T A T U S P O W E R Consumption One Week Propellant Remaining Output Margin Spacecraft (Gm) (Kg) Watts Watts Voyager 1 7 36.2 + 2.0 366 55 Voyager 2 6 39.3 + 2.0 370 61 ___ _____ ___ /_ /| /____/ \ /_ /| | | | | __ \ /| | | | Ron Baalke | baalke@mars.jpl.nasa.gov ___| | | | |__) |/ | | |___ Jet Propulsion Lab | baalke@jems.jpl.nasa.gov /___| | | | ___/ | |/__ /| M/S 301-355 | |_____|/ |_|/ |_____|/ Pasadena, CA 91109 | ------------------------------ End of SPACE Digest V12 #662 *******************