Date: Tue, 2 Mar 93 05:08:06 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V16 #248 To: Space Digest Readers Precedence: bulk Space Digest Tue, 2 Mar 93 Volume 16 : Issue 248 Today's Topics: A futurShades. Apollo Moon Missions ? A response from Anonymous Battery help needed! Blimps Bullets in Space Can Cassini Titan Probe float? Cassini Rover idea First Swedish space accident, Condolences.. Galileo Earth-Moon Animation Indian air-breathing solid rocket (2 msgs) JPL's 'faster, better, cheaper' goal Reboosting a denser station (was Re: payload return from Fred) Refueling in orbit (2 msgs) Spaceflight for under $1,000? SSF Resupply (Was Re: Nobody cares about Fred?) The Future of Fred Why Apollo didn't continue? 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: 27 Feb 1993 23:57:48 -0500 From: Pat Subject: A futurShades. Newsgroups: sci.space In article <1mm4u3INNcf8@gap.caltech.edu> looper@cco.caltech.edu (Mark D. Looper) writes: |The Solar Probe spacecraft, a proposed mission to whip by the sun at about |3 solar radii above the photosphere, will hide behind a big conical heat |shield of "carbon-carbon" (whatever that is) composite material. It will Carbon Fiber in a carbon based epoxy. I am sure coffman, or wingo or henry know the details of it. |not take pictures of the sun, but rather will carry instruments to measure |fields and particles that can come behind the shield to be observed; it |may also carry a camera to look _away_ from the sun to photograph light |backscattered off tenuous coronal material. The weird-o thing about this How about this. Deploy a small mirror over the edge of the cone, have light reflect off the mirror, onto a small imaging screen. Then have a camera point at the screen. With rocker servos on the mirror, one should be able to image quite a lot? |is that, whereas outer-planet spacecraft have to carry Radioisotope Thermal |Generators (RTG's) for power where sunlight is too weak for solar panels, |the Solar Probe will have to use RTG's where the sunlight is too _strong_ |for solar panels! Of course, in order to kill its angular momentum enough Hating to sound stupid, but why not put SunGlasses on the solar arrays. Not a polaroid film, but how about like those drilled aluminum ones. The aluminum is virtually impervious unless it passes the melting point, and if it's heavily mirrored, it should reflect 99% of the inbound thermal radiation. Make the drilled aluminum panels alrger then the solar cells, and you can spray the backs black and black body the waste heat to space. Am I missing something? One could build and test this on a small discovery class mission. And if aluminum is too low in heat tolerance, how about tungsten? ------------------------------ Date: Sun, 28 Feb 1993 00:39:40 GMT From: Henry Spencer Subject: Apollo Moon Missions ? Newsgroups: sci.space In article <13910.409.uupcb@the-matrix.com> roland.dobbins@the-matrix.com (Roland Dobbins) writes: >Missions were planned through Apollo 21, but funding was cut due to >Vietnam, etc. The immediate planning ran through Apollo 20, actually, but longer-range plans included two lunar missions a year on an ongoing basis. (Of course, the immediate plans were on firmer financial footing than the longer-range ones...) The break came at Apollo 20 because that's when the supply of Saturn Vs would run out, requiring major funding to re-start production. -- C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology effect since OS/360. | henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 26 Feb 93 23:21:48 GMT From: Dave Ratcliffe Subject: A response from Anonymous Newsgroups: news.admin.policy,alt.privacy,comp.org.eff.talk,sci.space,sci.astro In article , doug@cc.ysu.edu (Doug Sewell) writes: > Bruce Becker (bdb@becker.GTS.ORG) wrote: > : Anonymous postings are a really good example > : of things that are to be judged by content, > : since the typical responses of "oh that's a > : posting by X, he's an idiot", or "Aha, Y is > : always making good points" are not able to > : be made. > > No, one rapidly decides: > > "Oh, it's another post from an8785@anon.penet.fi. > > He's always casting about red herrings and and bold pronouncements like > 'having show that'... > > His posts aren't worth reading." Nope, we say: "Oh, It's another post from someone who has to hide behind an anonymous id." "Wonder what they're afraid of." One thing seems to be getting lost in all the rhetoric. Anonymous postings DO have their place, but not in groups like sci.space or any other similar groups. Examples of where they might well be acceptable have been posted already several times. Why doesn't anyone want to discuss this facet? -- vogon1!compnect!frackit!dave@psuvax1.psu.edu | Dave Ratcliffe | - or - ..uunet!wa3wbu!frackit!dave | Sys. <*> Admin. | | Harrisburg, Pa. | ------------------------------ Date: 28 Feb 93 02:46:05 GMT From: George William Herbert Subject: Battery help needed! Newsgroups: sci.space,sci.electronics,sci.aeronautics,sci.chem,sci.engr In article henry@zoo.toronto.edu (Henry Spencer) writes: >I think I'd look into the sexier battery technologies, like nickel-hydrogen >or silver-zinc, first. "Sexier battery technologies?" The Apollo spacesuits used silver-zinc nonrechargable batteries at nearly the power density (82 wh/kg) that current silver zinc batteries can get with a few recharges (102 wh/kg). Technology that's 35 years old is rarely sexy, though humans still may be. 8-) -george william herbert President, Retro Aerospace gwh@retro.com gwh@soda.berkeley.edu ------------------------------ Date: Sun, 28 Feb 1993 01:11:35 GMT From: Josh Hopkins Subject: Blimps Newsgroups: sci.space haw30@macaw.ccc.amdahl.com (Henry A Worth) writes: I wrote: >> >> If you were going to use beamed power (which isn't obvious to me) you would >> almost certainly use the huge surface area of the thing to mount your receiver. > Missed the first part of this, our news feed must be acting up again. >So please forgive if I retrace previous discussion. > While it would be nice to use some of that power to run the propulsion >system, how about using the beamed power - be it microwave, laser, or >whatever (reflected sunlight? probably too weeak) -- to directly heat >the blimp's envelope? It would certianly be possible to actively heat the lifting gas. However, given that Mars has an atmosphere of CO2 and probably has plenty of native Hydrogen available for use I don't forsee a real need for active heating. Passive lift should be just fine thank you. >For instance if using microwave, have a metalized >layer in the envelope material that is etched into little tuned antennae >and loads? There is some work being done on such things as inflatable antennas. I don't know how efficent it would be for power reception but I would assume it would be a strong candidate to fulfil your requirements. > Another approach would be a rigid half shell above the envelope that >could contain the receivers and/or heat exchangers and would double as >a shelter for the envelope and gondola. Since a hot-gas blimp would >substantialy collapse when cooled, the shell could descend over the >envelope and gondola, be anchored against storms and perhaps even >include active aerodynamic surfaces is to counter wind loading and >pitching. You don't really want a high performance balloon envelope to touch the ground. Another good reason not to count on active heating for lift (or at least not all of it). > Back to propulsion for a blimp (beam powered or otherwise). >Considering the thin atmosphere, and assuming a long-term/permanent >presence. If substantial subsurface water were found (almost a necessity >for a long-term presencence) any thoughts on what the preferable >propulsion method would be? I would assume that for any near term dirigible one would use an electric motor. It might be powered by a fuel cell or nukes, but solar power seems more likely. -- Josh Hopkins jbh55289@uxa.cso.uiuc.edu You only live once. But if you live it right, once is enough. In memoria, WDH ------------------------------ Date: Sun, 28 Feb 1993 03:28:38 GMT From: Brandon France Subject: Bullets in Space Newsgroups: sci.space I just started reading this newsgroup so if this question has been asked before please respond via email. What would happen if an astronaut was in a geostationary orbit and fired a rifle directly toward the earth? What path would the bullet take? Would the bullet actually hit the earth or would it assume some orbit? Brandon fsbgf@acad3.alaska.edu ------------------------------ Date: Sun, 28 Feb 1993 01:43:08 GMT From: Josh Hopkins Subject: Can Cassini Titan Probe float? Newsgroups: sci.space rabjab@golem.ucsd.edu (Jeff Bytof) writes: >Will the basic design of the Cassini Titan Probe allow it to >float if it lands on a liquid medium? If I recall corectly, yes. I believe it has sensors to determine its vertical orientation. Someone made a big deal out of the fact that this means you can measure "bobbing" of the probe, thus telling you something about the consistancy of the hypothetical sea and over the long term it would allow you to tell something about wave patterns. Rereading my post, it becomes obvious that I missed an important factor. We don't know exactly what Titans seas might be made out of. Therefore, at best we can say that it should float in the type of hydrocarbons we expect. Of course, if Titans turns out to be the way we expect, it it won't have been worth visiting :-) >How long will Cassini be in contact with the Titan Probe after >it enters the atmosphere? I don't know off hand. It should certainly be in contact at the planned time of landing. I think battery life is the constraint (rather than LOS of the orbiter) and that the planned life is for a "short while" after landing. I don't remeber how long a "short while" is, but I'm fairly sure it's a few hours at most. >Cassini goes on to Saturn orbit, correct? Affirmative. -- Josh Hopkins jbh55289@uxa.cso.uiuc.edu You only live once. But if you live it right, once is enough. In memoria, WDH ------------------------------ Date: Sun, 28 Feb 1993 01:33:41 GMT From: Josh Hopkins Subject: Cassini Rover idea Newsgroups: sci.space wbaird@dante.nmsu.edu (BAIRD) writes: > This is a bit of a hair brained proposal but I thought it might be a >possible idea for the Cassini mission.. > The idea is to have a relatively small autonomous rover on the Cassini >mission to get some mapping (visually) of the surface of Titan. It would >ideally weigh about 20 kg. It would drop in to the atmosphere of Titan with >the Huygens atmospheric probe. At the altitude of about 600 m it would be >jettisoned and a parachute deployed to slow the small aerial rover to lower >speeds. Uh, Huygens will do a very good job of slowing down to the low altitude you want, so it's not clear to me that jumping overboard gains you anything. The fans in the rover (three of them in a radially symmetric >configuration) would start up and allow the probe to hover at an altitude of >three meters. Lots of stuff deleted > Now that I have babbled about the idea, what do others think of it? >Too far fetched like the ice resupplying of SSF from the asteriod belt/outer >planets&moons? Questions, comments, suggestions? I hate to torpedo someone who's obviously put so much though into this but I have a very simple reply. Anyone who wants to design a rover for Titan that isn't a balloon has some serious explaining to do. Titan is probably the best place in the solar system for a balloon. Given that Titan is much to far away for teleoperation of an active probe and that we don't know enough about the surface or about AI to be able to design a good autonomous rover I don't see a big loss from the fact that a balloon can't be steered. Given that balloons can float _much_ longer than anything you want to design that uses active lift (and they do it more simply as well) they have major advantages there. If steering a serious requirment, Titan seems to be a benign enough environment to build a dirigible for. -- Josh Hopkins jbh55289@uxa.cso.uiuc.edu You only live once. But if you live it right, once is enough. In memoria, WDH ------------------------------ Date: Sat, 27 Feb 1993 23:39:14 GMT From: nsmca@acad3.alaska.edu Subject: First Swedish space accident, Condolences.. Newsgroups: sci.space In article , urf@icl.se (Urban F) writes: > A few hours ago, on the evening of Feb 27:th, a > German Orion sounding rocket undergoing calibration > at Esrange in the north of Sweden exploded. The > rocket was mounted horizontally, and its motor > ignited. It went through the wall, a wooden building > outside and exploded when it struck the next > house in line. So far one person is dead, three > injured, one critically. > -- > Urban Fredriksson urf@icl.se Condolences from Nome, AK.. And from Alaska in general.. Michael Adams NSMCA@ACAD@.ALASKA.EDU I'm not high, just jacked ------------------------------ Date: 28 Feb 1993 04:34 UT From: Ron Baalke Subject: Galileo Earth-Moon Animation Newsgroups: sci.space,sci.astro,alt.sci.planetary ============================== GALILEO EARTH-MOON ANIMATION February 27, 1993 ============================== The Galileo Earth-Moon Conjunction animation is now available at the Ames Space Archives. This animation is courtesy of Paul Geissler and Larry Kendall from the University of Arizona, with permission from Mike Belton, Galileo Imaging Team Leader. The animation was formed from 46 images taken by Galileo spaecraft shortly after its Earth flyby on December 16, 1992, and is in a compressed PICT format to be used with the NIH Image software on the Macintosh. Efforts to convert the animation to other formats is currently in progress. The animation is available using anonymous ftp to: ftp: ames.arc.nasa.gov (128.102.18.3) user: anonymous cd: pub/SPACE/ANIMATION files: Earth_Moon_Movie.Hqx Earth_Moon_Movie.txt -------------------------------------------------------------------------- Earth_Moon_Movie.txt Earth_Moon_Movie.Hqx is in BinHex format for the Macintosh. The unHexed file can be opened as a stack and animated by NIH Image, a public domain package available from Wayne Rasband at the National Institutes of Health. When uncompressed, the movie takes up about 6 Mb of memory. This is a time-lapse sequence taken by the Galileo spacecraft on December 16, 1992, eight days after its flyby of the Earth/Moon system en route to Jupiter. The 46 frames span 15 hours of motion by the Earth, Moon and spacecraft. These images were acquired with the 0.968 micron filter so that both vegetated and unvegetated land masses appear bright in contrast to the oceans. South is at top. Visible are the Pacific basin, Australia, Southeast Asia, India, and finally Arabia and the horn of Africa. A remarkable feature of this time-lapse sequence is the specular reflection or sun glint from the sea surface. Depending on the roughness of the water the extent of specular reflection varies rapidly, expanding over rough waters and contracting to a point over still oceanic pools such as near the west coast of Australia. Source: Paul Geissler and Larry Kendall, University of Arizona, with permission of M.J.S. Belton ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | If you don't stand for /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | something, you'll fall |_____|/ |_|/ |_____|/ | for anything. ------------------------------ Date: 28 Feb 93 01:56:08 GMT From: Josh Hopkins Subject: Indian air-breathing solid rocket Newsgroups: sci.space The most recent "Space News" reported on tests by ISRO of air breathing solid engines. They were apparently launched as the second stage of sounding rockets and acheived velocities up to Mach 23 (which SN then goes on to explain means 23 times the speed sound :-) As usual, SN just printed enough to arouse my curiosity. While I realize that part of the reason is because the data simply isn't available, I'd like to know more. I'm envisioning an AMROC "rubber rocket" with a Japanese LACE engine on top, but that seems a little more advanced than ISRO could handle in a tiny project. I can imagine other, simpler ideas but I can't convince myself that they could get off the ground. Anybody want to explain the design fundamentals for an air breathing solid booster? -- Josh Hopkins jbh55289@uxa.cso.uiuc.edu You only live once. But if you live it right, once is enough. In memoria, WDH ------------------------------ Date: 28 Feb 1993 02:54:46 GMT From: George William Herbert Subject: Indian air-breathing solid rocket Newsgroups: sci.space Go check out the last few years of the AIAA's "Journal of Propulsion" for good references on solid-fuel ramjets. THey're not really new, though a solid fuel scramjet (which is what this sounds like from what you posted) most definitely would be... -george william herbert Retro Aerospace gwh@retro.com gwh@soda.berkeley.edu ------------------------------ Date: 28 Feb 1993 00:05:38 -0500 From: Pat Subject: JPL's 'faster, better, cheaper' goal Newsgroups: sci.space,sci.astro,alt.sci.planetary I sincerely hope JPL can pull off the missions on the budget planned and in the time frames. We need to get more packages out to maore places then as we find interesting things, rapidly follow on with more advanced better oriented missions. Now let's see the other NASA centers buy into this philosophy. I think the DIscovery program will provide much needed balance to a psace science program dominated for 15 years by Great projects. pat ------------------------------ Date: Sun, 28 Feb 1993 00:37:51 GMT From: Henry Spencer Subject: Reboosting a denser station (was Re: payload return from Fred) Newsgroups: sci.space In article <1993Feb26.102807.1@fnalf.fnal.gov> higgins@fnalf.fnal.gov (Bill Higgins-- Beam Jockey) writes: >> a heavier station is *better*, because it reduces the frequency with >> which reboost is needed... > >This is because air resistance is kinder to a dense object than a >flimsy one, for equal surface area. But obviously you need to consume >more propellant to reboost the heavier station when it eventually >*does* need a reboost. Henry implies that this tradeoff is >favorable. Why? To a first approximation, the reboost fuel mass is independent of the station mass: the key requirement is that the thrust of the reboost engines, averaged over the period between reboosts, equal the average air-drag force on the station. Station surface area matters, because it affects drag, but mass is unimportant. The benefits of a heavier station come in secondary issues. There will be longer periods of uninterrupted microgravity between reboosts. The air-drag deceleration (one of the things that messes up the microgravity environment) will be lower. Reboost accelerations will be lower. And having things happen more slowly gives you more time to deal with problems that delay reboost or accelerate altitude loss. -- C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology effect since OS/360. | henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 28 Feb 93 02:48:56 GMT From: "Allen W. Sherzer" Subject: Refueling in orbit Newsgroups: sci.space In article <1mp2sjINNme2@phantom.gatech.edu> matthew@phantom.gatech.edu (Matthew DeLuca) writes: >>Suppose you are the PI of a multi-billion $$ Mars sample return mission. >>Are you going to risk your entire project on a technology which hasn't >>been done yet and which may or may not work? >So why do you expect NASA to do just that? I don't. What I expect is for NASA to anticipate these problems and chances for cost reduction and act on them. I agree that we should wait for them to work; the problem is NASA won't work the problems. >AS: "See, we can get cargo down with no problem at all for a fraction of the >cost of other methods...we just put it in a big can, stick some tiles on it, >and use a tether tied to the station to get it down." Yep. I assert working on such a system will save us billions every year if it works. NASA should be working on it. > >MD: "Nobody's tried that... Ah, but it HAS been tried and works quite well. The Russians and their primitive space program have been doing it for years. Surely your not saying our superior program can't duplicate it? Come to think of it, we have: Mercury, Gemini, and Apollo. Allen -- +---------------------------------------------------------------------------+ | Allen W. Sherzer | "A great man is one who does nothing but leaves | | aws@iti.org | nothing undone" | +----------------------108 DAYS TO FIRST FLIGHT OF DCX----------------------+ ------------------------------ Date: 27 Feb 1993 22:50:55 -0500 From: Matthew DeLuca Subject: Refueling in orbit Newsgroups: sci.space In article <1993Feb28.024856.26588@iti.org> aws@iti.org (Allen W. Sherzer) writes: >>MD: "Nobody's tried that... >Ah, but it HAS been tried and works quite well. The Russians and their >primitive space program have been doing it for years. Surely your not >saying our superior program can't duplicate it? Allen, did you read the article I wrote? I was referring to tethering objects down into the atmosphere as a return mechanism, as you have proposed in the past. Nobody's done it, not us, not the Soviets. -- Matthew DeLuca Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!matthew Internet: matthew@phantom.gatech.edu ------------------------------ Date: 28 Feb 1993 02:51:37 GMT From: George William Herbert Subject: Spaceflight for under $1,000? Newsgroups: sci.space In article henry@zoo.toronto.edu (Henry Spencer) writes: >"It" is launch vibration, higher radiation levels, and some complications >like the lack of convection for cooling. Assuming his hard disk survived >the trip up, and his cooling-fan setup was good enough to avoid problems >with overheating, John would find that his machine would work, but not >too reliably (especially when passing through the South Atlantic Anomaly, >where radiation levels are particularly high). More-or-less off-the-shelf >commercial laptops see extensive use for non-critical functions aboard >the shuttle, but the flight computers -- without which the orbiter cannot >be landed, among other things -- have to meet far more demanding specs. It is worthwhile noting, in these arguments, that if one works the numbers on how much dedicated radiation shielding is needed to make say a 486/33 space-rated as a package (a mini motherboard + various I/O cards and a hard drive within the shielding, and the power supply etc. external) that you get only moderate shielding (under 2" thick) and for a minimum package mass in the tens of kg you get more MIPS/kg with a well shielded current-tech chip than with older technologies that are rad-hard. This is not true of say the rad-hard RISC chips that (for one, AMD) has built for space applications, that combine the best of both worlds. But if you have the mass, and need the CPU, it can be done with current non space rated CPUs. -george william herbert Retro Aerospace gwh@retro.com gwh@soda.berkeley.edu ------------------------------ Date: 28 Feb 93 03:07:29 GMT From: George William Herbert Subject: SSF Resupply (Was Re: Nobody cares about Fred?) Newsgroups: sci.space In article steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes: >This is false; you repeatedly assume that the cost per pound is the >total operation cost+amortised cost divided by pounds flown; it is >no such thing - if NASA stopped in its tracks and flew nothing >it would still cost several billion per year. If that happened it wouldn't be a space program, it would be a jobs welfare program for space engineers and technicians. As it is a space program, a responsible accounting methodology is to sum its operations costs and divide by payload mass flown. If it stops being a space program then it stops getting treated as one for accounting purposes. Until then, it's irresponsible not to account that way. >Which is sheer fantasy, the $4 billion up front don't exist and >therefore there is no payback. NASA doesn't get a tax write off >for investments, if they reduce future operations they probably >just get less money to operate with. More importantly they never >get the upfront money in the first place - they certainly can't >borrow it on the open market! I would not attempt a project unless I had enough up-front financing to do it right. NASA can't get it, muddles along, and ends up wasting a lot of money. Is it better to do space programs this way? I don't know, political and policy issues related to space are a whole different ballgame than the economics. >This is pure nonsense. NASA is not a group of trading companies, >and its purpose is to find out how to carry out certain objectives, >if possible, given this years budget. They can't borrow upfront costs >and they are not free to buy from arbitary suppliers, a significant >part of their mission has been to find out how to carry out certain >objectives in space and to maintain a group of people who have the >experience of carrying out those activities. Yes, but if there are other paths to those activities that were not chosen for political reasons or for funding reasons, that would have been cheaper in the long run, you MUST acknowledge that the US taxpayer is getting less for his space dollars than he could BECAUSE OF THE POLITICAL SYSTEM HE HAS CHOSEN. On a purely technical level, the alternative methods are often blindingly obvious and easy, but our governmental structure won't allow itself to save money all the time. >Allen is wrong because he treats NASA as if it were a small business >operating in a free market, and it isn't. It is not at all clear to >me that it should be either. That's a flaw of Allen's posts, agreed. He's pointing out idealized technical solutions in what currently is a massively muddled technical, political, social, economic, and media problem. There is nothing wrong with doing this: a reasonable goal for a space program might be to change its external environment so that it can operate more reasonably at the technical level that it should be most concerned with. Deciding to do so is a necessary prerequisite for implimenting teh "quick technical fixes" that come up so often here, and is rarely discussed because it's so massive a problem that it often can't be solved except by top-down fiat, rare in this age. -george william herbert Retro Aerospace gwh@retro.com gwh@soda.berkeley.edu ------------------------------ Date: 27 Feb 1993 23:42:02 -0500 From: Pat Subject: The Future of Fred Newsgroups: sci.space I remember talking to Henry back in 1988? maybe 89? last time you were in DC about this. Back then we both thaought it was terribly silly of an idea. I am sure, Doug, Gary and Dennis can all find good reasons for why it was even proposed, and how great it would have been except for those communist congressmen and foreign devils with their ideas on standardization. pat ------------------------------ Date: Sun, 28 Feb 1993 00:45:46 GMT From: Henry Spencer Subject: Why Apollo didn't continue? Newsgroups: sci.space In article car57812@uxa.cso.uiuc.edu (Charles Adam Rummel) writes: >They used the left-over Saturn parts to make Skylab, but was that because >they had run out of LEM/CSM and rovers or had too many Saturns, or...??? All the Apollo and Saturn V hardware for Apollos 18-20 was on hand; the cancellations were for financial reasons, not lack of hardware. Going past Apollo 20 would have required re-starting the Saturn V production line. Somewhere around Apollo 22, I think, the spacecraft production lines would likewise have required restarting. Skylab was planned around an S-IVB stage basically because it was a convenient large pressure hull that could easily be put into orbit as the second stage of a Saturn IB. That approach, the "wet workshop", would have required that Skylab be refitted into a lab after reaching orbit. It probably would have worked, but it wasn't easy. When Apollo 20 was cancelled, it became possible to release a Saturn V to launch Skylab fully equipped -- the "dry workshop" -- and that did make things easier, so it was done. -- C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology effect since OS/360. | henry@zoo.toronto.edu utzoo!henry ------------------------------ End of Space Digest Volume 16 : Issue 248 ------------------------------