Date: Wed, 16 Dec 92 05:00:21 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #549 To: Space Digest Readers Precedence: bulk Space Digest Wed, 16 Dec 92 Volume 15 : Issue 549 Today's Topics: Aurora (2 msgs) DC-X cost figures (was : Terminal Velocity of DCX?) liquid fuels (2 msgs) range safety Relay to Follow Galileo? (2 msgs) Returned mail: Unable to deliver mail (2 msgs) Saturn history Solid fuel rockets SSF Budgets '88' -> '92' Stationary 'orbits' over the poles Terminal Velocity of DCX? (was Re: Shuttle ...) (5 msgs) What is a VSAT? 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: Tue, 15 Dec 92 15:57:37 MET From: PHARABOD@FRCPN11.IN2P3.FR Subject: Aurora Dean Adams writes (Fri, 11 Dec 92 13:49:51 GMT): >>The first sightings (1990-1991) were of a "primarily delta-shaped" >>aircraft. (J. Pharabod) >Not really... The first reported Aurora design ideas were of a smaller >"almond" shaped sort of vehicle, also called the "pulser". The more >recent reports seem to be of something much larger. (D. Adams) I was speaking only of the sightings reported in the August 24, 1992, AW&ST issue. I was not speaking of previous articles, such as: "Possible 'Black' Aircraft Seen Flying In Formation With F-117s, KC-135s" AW&ST, March 9, 1992 (p. 66) "New Evidence Bolsters Reports of Secret, High-Speed Aircraft", AW&ST, May 11, 1992 (p. 62) >>Only in the two last sightings (1992) were reported a "narrow >>fuselage" and/or a "forward wing or canard". Maybe these two last >>sightings can be discarded >WHAT?? The previous reports were based on "design concepts", >these are much more direct reports. There is no logical reason >for simply "discarding" such information. I still think that the sightings reported in this August 24 issue are not better than UFO sightings: 1. 1990 sightings: occurred during night or late evening (visibility?), number of witnesses not reported, apparently no inquiry about the witnesses (tired? drunk? ill?) 2. April 1991 sighting: daytime, but the craft was said "dwarfing an F-16 chasing it". This casts a doubt on this sighting: is it usual that US military planes chase US secret aircrafts? (well, maybe it was an exercise). Same questions about the witnesses. 3. May 10, 1992: daytime over Atlanta suburbs, but only one witness in a populated area. Why other people did not see or report anything? 4. July 12, 1992: during night, only one witness (a motorist), no inquiry reported about this witness. 5. No photos, no video films. >>3). In its December 1991 issue, Popular Mechanics (article "America's >>New Secret Aircraft") reports, near Edwards AFB, a big triangular object >>which, like the Belgian object, can hover silently horizontally and >>vertically... >99% of that article consisted of repeating the previous AW&ST report. >Then they threw in that one extra report. It did not sound like it >was very highly substantiated... It was no more substantiated than the above criticized sightings. However, since the object was hovering or flying at very low speed, the sightings lasted for more than a few seconds, which was probably not the case for the AW&ST sightings: "[...] The craft moved so slowly one observer said he could jog along with it.[...] Observers who followed the craft long enough detailed unlikely maneuvers in which the vehicle stopped, rotated in place and hovered vertically, presenting a thin trailing edge to the ground." >>c) Popular Mechanics and AW&ST are no more serious than UFO reviews. >Strike Three. :-> Where is the logic there? I can't speak for P.M., >but have you ever read AW&ST? It is VERY serious. Yes, I have read it. It's generally serious... except when it reports sightings. In this last case, it seems no more serious than UFO reviews (at least I think so, since I don't read UFO reviews). J. Pharabod ------------------------------ Date: Tue, 15 Dec 92 17:28:24 MET From: PHARABOD@FRCPN11.IN2P3.FR Subject: Aurora Brad Whitehurst writes (Thu, 10 Dec 1992 23:31:26 GMT): > I'll believe AW&ST over the Wall Street Journal and Pop >Mechanics any day! They've got an intelligence net second only to the >CIA...hmmm, mebbe even better! Sounds generally true, but when they report sightings, they don't look very serious. See my answer to Dean Adams on sci.space this day for more details. J. Pharabod ------------------------------ Date: Tue, 15 Dec 1992 10:07:45 -0600 From: pgf@.cacs.usl.edu.cacs.usl.edu (Phil G. Fraering) Subject: DC-X cost figures (was : Terminal Velocity of DCX?) >Also note that the cost of one Shuttle flight is about the same >as the entire DC development program. \I believe that's the cost of the DC-X development, which will not /be manned, or achieve spaceflight. Believe what you want, but DC-X has a budget (the last I heard) of about $ 50 million dollars. Or 10 % the cost (yup, 1/10th!) of a shuttle flight. Remember, people developed the SR-71/A-12 out of much more intractable materials than the composites being used for DC-X, with their main design tools being pen and ink and slide rules, for a cost less than that of launching the shuttle once. Sooner or later someone is bound to try to use CAD/CAM and sophisticated materials to lower costs instead of to increace them. \ Also, if Shuttle, which is hung from the SIDE of a giant cryogenic / fuels tank, cannot meet safety requirements, how will DC-1, in which \ the crew will ride sandwiched between two cryo tanks? Actually, the way the Shuttle has the cryogenic tank hanging off to one side is much more dangerous than DC-X, where the tanks are actually integrated into the structure. \ I also wonder how much safety provisions could be built for a / passenger module located in this area. I'm not saying Shuttle is \ safer or more dangerous, just that both have considerable safety / problems to overcome, and trumpeting about DC passenger accomodations \ is definitely premature. / -Brian If one costs 1/10 as much to fly as the other, it could actually be more dangerous and still pay off... the flight insurance will just be a _little_ more expensive, that's all. Besides, what was it that Mary Shafer said a while back? -- Phil Fraering "...drag them, kicking and screaming, into the Century of the Fruitbat." <<- Terry Pratchett, _Reaper Man_ PGP key available if and when I ever get around to compiling PGP... ------------------------------ Date: 15 Dec 92 03:27:09 GMT From: BrianT@cup.portal.com Subject: liquid fuels Newsgroups: sci.space >What does the payload of the shuttle have to do with how screwed up the >design of the SRB o-rings??? That is what caused the accident in the first >place. Why would limiting payload perpellent make a difference??? > > -- Ryan Korniloff > -- rkornilo@nyx.cs.du.edu Ryan... After Challenger was lost, NASA reviewed the entire program (better late than never) and discovered a host of systems and procedures which had little, if any, backup safety measures. The O-rings were the first of many problems corrected during the 1986-88 downtime. Others were certain elements of the Main Engines and a potentially disastrous flaw in the LH2 fuel lines between the Shuttle and Tank. They also scrapped Shuttle-Centaur because the Centaur was too heavy for a safe landing in an emergency situation. There was no way to dump the Centaur's fuel safely in the time available before landing. -Brian ------------------------------ Date: Mon, 14 Dec 92 17:52:18 PST From: Brian Stuart Thorn Subject: liquid fuels Newsgroups: sci.space >Sorry, wrong. Cryogenic fuels fly in the payload bay on every extended- >duration shuttle flight. The shuttle's fuel cells use liquid hydrogen >and liquid oxygen, and the extended-duration pallet for the cargo bay >(first flown recently) is basically a set of LH2 and LOX tanks. Well, it's only flown once actually. Why on earth isn't EVERY Columbia mission an EDO mission? Budgets? Anyway, the EDO pallet doesn't carry anything like the amount of LH2 Centaur would have had. >Shuttle/Centaur, the launch system originally meant for Galileo (as well >as the other two, but it was the massively-overweight Galileo mission >that drove its specs), died partly because of an acute attack of timidity >after Challenger, partly because people distrusted some aspects of Centaur's >construction, and partly because Centaur+Galileo was so heavy that it led >to problems like needing to jettison its fuel before an emergency landing. >A somewhat smaller LOX/LH2 stage with more conservative construction could >probably be certified for shuttle use even now, but nobody wants to try. Thank goodness it didn't fly on Shuttle. Whatever GD did to make Centaur more powerful for the Shuttle was a real headache. The thing has failed twice in the last year or two. If that had happened on a Shuttle launch, we'd never have heard the end of it from the anti-shuttle folks. -Brian ------------------------------ Date: Tue, 15 Dec 92 10:47 EDT From: Subject: range safety Say Paul could you give us a little more info on your club/launch groupe. Are you with tripolee or some other club? How do you verify altitudes in excess of 50k ft.? What is the procedure for (routiinely recieving waivers up to 100k ft.) Thanks beaufait@cebaf2.cebaf.gov ------------------------------ Date: 15 Dec 92 03:27:47 GMT From: BrianT@cup.portal.com Subject: Relay to Follow Galileo? Newsgroups: sci.space >Well why did the HGA have to be cloed up in the first place? If it is too >big, then couldn't they have used a more powerful transmitter? I would >have rather tried to avoid such a chance for failure. If thay don't get >that HGA open then %30-%40 of the mission objectives will be lost. Or is >the radio frequncy have something to do with he size of the HGA??? > > > -- Ryan Korniloff > -- rkornilo@nyx.cs.du.edu Ryan... Galileo's umbrella-type High Gain Antenna was left in the folded position because it was thought that the high temperatures it would encounter during the Venus flyby portion of the mission could warp the antenna. They attempted to open the antenna only after the Venus flyby, when Galileo flew farther from the Sun. It was jammed. Cassini, I think, will have a standard hard HGA, similar to the Voyager and Magellan antennae. I hope the Galileo problem does not prevent future spacecraft from using the folding antenna design. It worked quite well on the TDRS satellites. -Brian ------------------------------ Date: 14 Dec 92 23:19 EST From: wlmss@peg.pegasus.oz.au Subject: Relay to Follow Galileo? Newsgroups: sci.space Subject: Re: Relay to Follow Galileo? Further to the above I hear per email ( and I thank the Sender): > This was discussed to death several months ago, so people probably didn't > re-open the discussion. The optimum time to launch a relay satellite is > NOW (galileo is on the optimal hoffman trajectory). Launching it next year > will take considerably more fuel, and no such craft is even on the planning > books. This is astonishing! Surely to NOT chase the thing is too costly! Dosen't the media, public & govt understand? If a relay is feasible the issue is the need to alert the uninformed wider public to what is being lost. The media. The public. And what about commercial sponsorship? Have any or all channels been exhausted? What if a few high profile persons spoke up at once? To think the galilean vistas were within reach of humanity - and now this! **** Lawrie Williams ------------------------------ Date: Thu, 10 Dec 92 14:42:50 -0800 From: Mail Delivery Subsystem Subject: Returned mail: Unable to deliver mail ----- Transcript of session follows ----- 554 Address too long ----- Unsent message follows ----- Received: by ucbvax.Berkeley.EDU (5.63/1.43) id AA27052; Thu, 10 Dec 92 14:42:50 -0800 Received: from USENET by ucbvax.Berkeley.EDU with netnews for space-usenet@andrew.cmu.edu (space@andrew.cmu.edu) (contact usenet@ucbvax.Berkeley.EDU if you have questions) Date: 2 Dec 92 18:57:09 GMT From: dog.ee.lbl.gov!overload.lbl.gov!agate!usenet.ins.cwru.edu!magnus.acs.ohio-state.edu!zaphod.mps.ohio-state.edu!saimiri.primate.wisc.edu!usenet.coe.montana.edu!ogicse!das-news.harvard.edu!cantaloupe.srv.cs.cmu.edu!crabapple.srv.cs.cmu.edu!C161A_30%ipfw.BITNET%husc6, .harvard.edu@ucbvax.Berkeley.EDU ("ZALBAR DELPHI, MAIL::GOD") Organization: [via International Space University] Subject: DC-1 & landing in bad weather Message-Id: Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu I'm kinda curoius... What effect would a wind shear have on a taildown landing of a DC-1... How about cross winds... The whole things SOUNDS pretty workable... but if the DC-1 comes in on empty tanks (or nearly so), what if the craft has to divert to an alternate site... As George Carlin says, "The only unsceduled landing I'm afraid of is the one in the cornfield on the far side of the airport..." Which brings another point... Could (being realistic now) the DC-1 set down on ANY more or less flat surface, like a cornfield... Or would that result in a forest fire (er popcorn...). =============================================================================== Chris Sheldon C161A_30@cvax.DECnet C161A_30@cvax.ipfw.indiana.edu Zalbar Delphi, Mominium =============================================================================== ------------------------------ Date: Thu, 10 Dec 92 21:02:35 -0800 From: Mail Delivery Subsystem Subject: Returned mail: Unable to deliver mail ----- Transcript of session follows ----- 554 Address too long ----- Unsent message follows ----- Received: by ucbvax.Berkeley.EDU (5.63/1.43) id AA22305; Thu, 10 Dec 92 21:02:35 -0800 Received: from USENET by ucbvax.Berkeley.EDU with netnews for space-usenet@andrew.cmu.edu (space@andrew.cmu.edu) (contact usenet@ucbvax.Berkeley.EDU if you have questions) Date: 2 Dec 92 23:04:14 GMT From: dog.ee.lbl.gov!overload.lbl.gov!agate!usenet.ins.cwru.edu!magnus.acs.ohio-state.edu!zaphod.mps.ohio-state.edu!saimiri.primate.wisc.edu!usenet.coe.montana.edu!ogicse!das-news.harvard.edu!cantaloupe.srv.cs.cmu.edu!crabapple.srv.cs.cmu.edu!amon%elegabalus.cs.qub.ac, .uk@ucbvax.Berkeley.EDU Organization: [via International Space University] Subject: Re: Shuttle replacement Message-Id: Sender: space-request@andrew.cmu.edu To: space@andrew.cmu.edu > It seems to me that the launch requirement for something of the DC class > is small enough that there will only be a few built, and those flown > fairly infrequently. At least they will fly at nowhere near the schedule > rates of airliners. What I'm questioning here is whether airliner grade > ground servicing can work with such a system. It would take many years > of flight experience to feel confident that all the catastropic failure > Max Hunter's own words are that he is not out to build a hanger queen like the space shuttle. This bird is meant to get the pants flown off it. If DC-X works, and then DC-Y works, the DC-1 will be open for business to carry passengers into orbit. And before you talk about it being dangerous... well, as far as I'm concerned, *LET* all the chickenshits stay on the ground. Who needs them out there anyway? I certainly don't expect an operational DC-1 to be any less safe than commercial airtravel in the 1920's. Otherwise it won't be built. If grandpa and grandma had the guts to do travel in their day, then so do I in mine. -- ======================================================================= Give generously to the Dale M. Amon, Libertarian Anarchist Betty Ford Home for amon@cs.qub.ac.uk the Politically Correct Greybook: amon%cs.qub.ac.uk@andrew.cmu.edu ======================================================================= ------------------------------ Date: Mon, 14 Dec 92 17:50:37 PST From: Brian Stuart Thorn Subject: Saturn history Newsgroups: sci.space >The Saturn I/Centaur configuration is the original Saturn I multistage vehicle >I confirmed this when re-reading General Medaris's book. He specifically >names the Centaur as the Saturn I upper stage. >The Centaur was considered as the upper stage (4th) for the Saturn V. That was >to support the Grand Tour by the original Voyagers. This little beastie had >the Nerva as the Third stage with the Centaur as the 4th! Man Talk about >Delta V or lift capability! I saw this scenario carefully laid out in one of >the Marshall books on what was called the "Apollo Applications Program". This >little configuration could lift two Voyager class full up ground tours. Would >have been cool wouldn't it. > >Dennis, University of Alabama in Huntsville Thanks, Dennis. But I believe the previous message said that Centaur had actually flown on a Saturn 1. You point out that Medaris planned this, but I don't think it ever happened. -Brian ------------------------------ Date: Fri, 11 Dec 92 09:36:23 EST From: "Duncan J. Melville" Subject: Solid fuel rockets > Date: Tue, 8 Dec 1992 13:43:21 GMT > From: Gary Giles > Subject: Cryogen costs > > In article John Roberts, > roberts@cmr.ncsl.nist.gov writes: > >In article John Roberts, > roberts@cmr.ncsl.nist.gov writes: > >...I've never been able > >to find out where NASA gets the fuel (they have big spherical tanks, but > that > >doesn't necessarily mean it's produced on-site), or what they do with the > >stuff that's drained out of the tanks when a launch attempt is cancelled. > > I saw a NASA report detailing a plan to ship coal to Florida and So, that's what they mean by solid fuel! Duncan J. Melville Dept of Mathematics St. Lawrence University Canton, NY 13617 dmel@slumus.bitnet ------------------------------ Date: 14 Dec 92 16:09:27 GMT From: tffreeba@indyvax.iupui.edu Subject: SSF Budgets '88' -> '92' Newsgroups: sci.space SSF Budgets '88' - '92' in $millions Requested Recieved % of request 1988 767 393 51% 1989 967 900 93% 1990 2050 1750 85% 1991 2451 1900 77% 1992 2029 2029 100% * SSF Media Handbook 1992 ------------------------------ Date: Tue, 15 Dec 92 17:17:47 EST From: Tom <18084TM@msu.edu> Subject: Stationary 'orbits' over the poles In article , 18084TM@msu.edu (Tom) writes: |> For the poles, forget about tethers. What you want is some kind of giant |> charged ring that you use sunlight to spin, creating a force from the |> magnetic field of the Earth that balances gravity... James Reed asks: >Yeah, but what happens next time the Earth's magnetic field reverses? > :-) :-) Good question. I guess you either ride the change (if it's graudal) over to the other pole or just reverse the current (if it's quick). Or, you take the opportunity, before the reversal, to build a whole bunch of supports to the whole ring, until it's completely self-supporting, removing your dependence on the magnetic field, or on a continuous supply of energy! Ha ha! Gaia's Halo! -Tommy Mac -----------------------------============================================ Tom McWilliams | What a tangled web we weave, when at ". | 18084tm@ibm.cl.msu.edu | , .first we .practice .*' .| (517) 355-2178 -or- 353-2986| '. ' . . to decieve , | a scrub Astronomy undergrad | After that, the , + | at Michigan State University| improvement is tremendous! '. , .' | ------------------------------=========================================== ------------------------------ Date: 15 Dec 92 03:26:36 GMT From: BrianT@cup.portal.com Subject: Terminal Velocity of DCX? (was Re: Shuttle ...) Newsgroups: sci.space >Not quite. It wold take about 1.5 years of Shuttle funding to develop DC. Now >for the cost of a Shuttle flight, you could run a program to answer all the >open technical questions and have enough left over to buy a Titan IV to >launch the payload which would have gone up in the Shuttle. > > Allen Assuming everything works right, Allen. In the history of spaceflight, that has seldom been the case. -Brian ------------------------------ Date: 15 Dec 92 03:57:59 GMT From: kentm@rebecca.its.rpi.edu Subject: Terminal Velocity of DCX? (was Re: Shuttle ...) Newsgroups: sci.space >Now >for the cost of a Shuttle flight, you could run a program to answer all the >open technical questions and have enough left over to buy a Titan IV to >launch the payload which would have gone up in the Shuttle. > Allen That a DC-X and a Titan IV launch could be had for the cost of a Shuttle mission I believe. What I don't believe is that you'd get any knowldgeable volunteers to fly a Spacelab mission on a Titan IV. Mike -- Michael Kent kentm@rpi.edu Flight Test Engineer Tute-Screwed Aero '92 McDonnell Douglas Rensselaer Polytechnic Institute These views are solely those of the author. Apple II Forever !! ------------------------------ Date: 15 Dec 92 03:26:00 GMT From: BrianT@cup.portal.com Subject: Terminal Velocity of DCX? (was Re: Shuttle ...) Newsgroups: sci.space >Nope. You might get more than 10 people in it, but it would >never get off the ground. NASA studied this idea years ago. >It was dropped because it couldn't meet minimum safety requirements. > >Also note that the cost of one Shuttle flight is about the same >as the entire DC development program. I believe that's the cost of the DC-X development, which will not be manned, or achieve spaceflight. Also, if Shuttle, which is hung from the SIDE of a giant cryogenic fuels tank, cannot meet safety requirements, how will DC-1, in which the crew will ride sandwiched between two cryo tanks? I also wonder how much safety provisions could be built for a passenger module located in this area. I'm not saying Shuttle is safer or more dangerous, just that both have considerable safety problems to overcome, and trumpeting about DC passenger accomodations is definitely premature. -Brian ------------------------------ Date: Tue, 15 Dec 1992 18:21:11 GMT From: "Edward V. Wright" Subject: Terminal Velocity of DCX? (was Re: Shuttle ...) Newsgroups: sci.space In <1992Dec11.175719.24880@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes: >Snide remarks not withstanding, chamber pressure isn't the only form >of stress on a vehicle. While I like Truax's Sea Dragon proposal >on several grounds, the low chamber pressures lead to very high >loads on the turbopumps because so much more fuel per unit time >has to flow to achieve the high thrust required with low pressure >engines. Reducing stress in one area can lead to increased stress >in another area when the objective remains to get a vehicle from >surface to orbit in a single leap. The high speed pumps, not combustion >chamber stresses, are the main reliability concern of liquid fuel rockets >anyway. I'm sure that Truax, who worked alongside Robert Goddard, will appreciate your educating him about the main concerns in building liquid rockets. :-) >>No, it's not. The mass of propellent required for a vertical landing >>is much less than the weight of the wings. The only way you can possibly >>come out ahead is if you use the wings for lift on both takeoff and landing. >I'm not convinced this is true, especially if most of the "wing" is really >lifting body. Also the fuel is not the only mass penalty of VTOL, bigger >tankage and structure are required as well. Again, people like Truax are convinced, and they have the advantage of actually having done the math. You are completely adamant about not believing anyone who has done the math, yet have never shown us any figures of your own to prove they are wrong. If you don't do the math, it isn't science, it's opinion. ------------------------------ Date: Tue, 15 Dec 1992 18:28:28 GMT From: "Edward V. Wright" Subject: Terminal Velocity of DCX? (was Re: Shuttle ...) Newsgroups: sci.space In <1992Dec13.174759.9626@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes: >If the cost per pound of space transportation drops enough, we won't want to >do *any* space assembly since that's very expensive, difficult, and time >consuming. Only if space transport remains high cost will space assembly >be worthwhile, at least until we are much further down the learning curve >of doing assembly work in space. Difficult? Nah. No more so than working under water. How many man-hours of SCUBA experience and experimentation were required before divers started to get much work done? How does that compare with the number of man hours that have been spent in EVA? How often do astronauts have their work interrupted by a passing shark. Expensive? If it becomes inexpensive to get workers into space, to get materials into space, and to get equipment into space, why should assembly and construction work be expensive? This is a technological superstition. "It will always that way, because that's the way it's always been." "Aluminum has always been more expensive than platinum and gold, and always will be." Time consuming? Again, if transportation costs drop, so do life- support costs. People can afford to stay in space for longer periods of time, so they have time to do the job. Where's the problem? >>True, a passenger version of the DC-1 couldn't carry more than >>about 20 people. Of course, the Shuttle can only carry 7-10. >>What's your point? >The Shuttle can carry large *working* crews while the proposed DC would >carry sardine packed *passengers* because there's no room for them to work. >That point should be obvious. Well, you got me there. Yeah, the DC will be just like the old DC-3, or the modern B-747. Passengers are crammed in like sardines. No room for them to work. But I'll think you find that most people who fly on business don't do their business on the plane anyway. An airliner makes a poor factory and a lousy hotel. >>I don't really see why not, as long as the arm can be folded to >>fit the DC's cargo bay. Of course, a man in a space suit is more >>versatile than Canadarm and, if the transportation costs are low >>enough, cheaper too. >The current arm cannot be made to fit the proposed DC payload bay, >a new one would have to be designed with either considerably less >capability, or some very intricate folding geometry. That's probably >only a billion dollar project so it would likely be done if DC works >out. The complicated part of the arm is the joints. Shortening the length of the pipes between the joints shouldn't be a major undertaking. >Spending two days in a spacesuit isn't likely to be either practical >or cost efficient. As we've found out from Shuttle, work in a suit is >slow and cumbersome. Yeah. We've got tens of hours of experience, so that settles that.... Obviously there are no new ideas left to try. >Some things are just easier with a bigger vehicle that has both a crew >space *and* a cargo bay at the *same* time and that can stay in orbit >for 10 to 30 days. A service station needs a repair bay, a work crew, and enough time to do the job. I don't understand why it needs to be a transportation system also. Most garages own a tow truck. I've never seen a garage that was a tow truck. >Rockets aren't more complex, an SRB has fewer moving parts than a 747 >engine for example. But that doesn't automatically mean that an SRB >is cheaper per mile to operate. If you scrapped the 747 after one flight, or crash-landed it in the ocean, then towed it back to land for refurbishment up to ten times, it would be much more expensive than the SRB. >Jets have massive amounts of "free" air to feed them oxygen and to >cool them. But LOX is cheap, and you've just said that propellents are a small part of the cost. >They have the benefit of wings to bear most of the loads so that >they don't have to support the vehicle by brute force as well as >move it horizontally to it's destination. Wings also produce drag. >They operate at lower temperatures and pressures than >rocket engines. And their fuel is non-corrosive and storable at >room temperature (though some lower performance rockets share this >feature) Liquid hydrogen, methane, propane -- none of those are corrosive. LOX is corrosive, but so is the gaseous O2 used by turbojets. Look in the Yellow Pages under "bottled gas" and find out how hard it is to store liquid propane at room temperature. >Rockets have to work in a more hostile and varied environment >than jets. So, when was the last time LEO was hit by a blizzard, typhoon, thunderstorm, monsoon, tornado, or hurricane? >Man has been building rockets for 2,000 years while he has >only been building jets for 50, I think the ancient Greeks, who built a working jet engine, lived a little more than 50 years ago. ------------------------------ Date: 14 Dec 1992 09:42:32 GMT From: Dieter Kreuer Subject: What is a VSAT? Newsgroups: sci.space In article <1992Dec11.175249.21479@athena.mit.edu>, mock@space.mit.edu (Patrick C. Mock) wrote: > > > Does anyone know what does VSAT (Very Small Aperature Terminal) mean > in the context of satellite communications? It means an earth station with a very small dish (and therefore limited power and sensitivity). There are VSATs which fit inside a briefcase, with the dish inside the lid. The signal emitted by a VSAT is too weak to be directly received by another VSAT, therefore, there is a so called hub-station in the middle of the net, which has a much bigger dish and sensitivity, so that it can receive all the stations in the net and retransmit their messages with higher power. The hub transmis- sions can then be received by the VSATs. So, you need two satellite "hops" to communicate with another VSAT. The increased propagation delay, the channel access scheme and the high bit error probability of this low link budget communication leads asks for special communication protocols, which distinguish VSATs form other satellite communication systems. ----------------------- --------------------------------- Dieter Kreuer ## ======== / dieter@informatik.rwth-aachen.de Lehrstuhl Informatik IV __ /// /# / dieter%informatik.rwth- RWTH Aachen ## /// # # / aachen.de@uunet.uu.net Ahornstr. 55 ## /// ##### /...!informatik.rwth-aachen.de!dieter W-5100 Aachen, Germany ==== # / PHONE: +49 241 80 21413 ------------------------------ End of Space Digest Volume 15 : Issue 549 ------------------------------