Date: Thu, 12 Nov 92 05:04:30 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #412 To: Space Digest Readers Precedence: bulk Space Digest Thu, 12 Nov 92 Volume 15 : Issue 412 Today's Topics: Apollo fire Lunar "colony" reality check (4 msgs) Lunar "colony" reality check and Apollo fire (2 msgs) Man in space... Man in the loop NASA is too big O2 spacecraft (was Re: Lunar "colony" reality check) Obscure Help Needed (3 msgs) oxygen atmospheres Pioneer 6 Update - 11/11/92 Sikhote-Aline-Meteorite (was Re: "Earth Gains a Retinue of Mini-Ast.") The Big Picture What kind of computers are in the shuttle? Where are Pioneer and Voyager Headed? 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: Wed, 11 Nov 92 18:37:53 GMT From: "John P. Mechalas" Subject: Apollo fire Newsgroups: sci.space,alt.sci.planetary In article mheney@access.digex.com (Michael K. Heney) writes: >Finally, the image of being killed by Velcro is mind-boggling. (Lunatic >Loop-strips! Hook-strips from Hell!) Toxic fumes in the smoke were the >cause of death - burning velcro could have been one source, but wiring, >insulation, etc also contributed. The burn rate of the velcro and nylon was so rapid that they were the most likely contributors to the toxic fumes that led to the deaths outright. Kinda makes you lose faith in synthetics, doesn't it? :) What's also sad about the whole affair, was that Harrison Storms was turned into the scapegoat at the end. He wasn't even allowed on the launch site of the Apollo 12 mission, and he had been basically the centerpiece of the whole Apollo project... -- John Mechalas "I'm not an actor, but mechalas@gn.ecn.purdue.edu I play one on TV." Aero Engineering, Purdue University #include disclaimer.h ------------------------------ Date: Wed, 11 Nov 92 16:39:40 GMT From: "John P. Mechalas" Subject: Lunar "colony" reality check Newsgroups: sci.space,alt.sci.planetary In article <1992Nov11.143903.17831@news.weeg.uiowa.edu> jboggs@umaxc.weeg.uiowa.edu (John D. Boggs) writes: >From article <1992Nov11.020940.4767@gn.ecn.purdue.edu>, by mechalas@gn.ecn.purdue.edu (John P. Mechalas): >> >> This is true for the most part, but at high O2 pressure, normally inflammable >> objects burn quite well. So in that respect, it is indirectly a fire >> hazard...sort of. :) >> > >Actually, normally inflammable objects burn quite well at sea-level pressure >of pure *air*. However, you need the high pressure to get normally >*non*flammable objects to burn. [high pressure O2] I guess that explains why I'm not an English major, huh? :) I'll get this "in-" "non-" thing straigthened out one of these days... -- John Mechalas "I'm not an actor, but mechalas@gn.ecn.purdue.edu I play one on TV." Aero Engineering, Purdue University #include disclaimer.h ------------------------------ Date: Wed, 11 Nov 1992 17:01:05 GMT From: "Phil G. Fraering" Subject: Lunar "colony" reality check Newsgroups: sci.space,alt.sci.planetary In article <1992Nov11.143433.18514@news.weeg.uiowa.edu> jboggs@umaxc.weeg.uiowa.edu (John D. Boggs) writes: >From article <1992Nov11.005151.15358@jpl-devvax.jpl.nasa.gov>, by jenkins@fritz (Steve Jenkins): >> >> Oxygen, like many gases, has narcotic effects at very high pressures, >> such as in deep-sea diving. It can cause blindness in newborns >> >Yes to blindness in newborns, but it is the *nitrogen* that has the narcotic >effect in deep sea diving -- hence the use of helium for the really really >deep dives. >Trust me, I'm a librarian. _MAYBE_ to blindness in newborns. There are anti-blindness drugs that apparently sometimes work and have been used on newborns who are born with lung disorders and need pure oxygen in their first weeks of life. I personally ;-) know of _one_ case... -- Phil Fraering In the country of the blind.... 60 minutes doesn't run stories about people trying to ban hearing implants! ------------------------------ Date: 11 Nov 92 17:52:42 GMT From: Carl J Lydick Subject: Lunar "colony" reality check Newsgroups: sci.space,alt.sci.planetary In article <1992Nov11.143433.18514@news.weeg.uiowa.edu>, jboggs@umaxc.weeg.uiowa.edu (John D. Boggs) writes: =From article <1992Nov11.005151.15358@jpl-devvax.jpl.nasa.gov>, by jenkins@fritz (Steve Jenkins): => => Oxygen, like many gases, has narcotic effects at very high pressures, => such as in deep-sea diving. It can cause blindness in newborns => = =Yes to blindness in newborns, but it is the *nitrogen* that has the narcotic =effect in deep sea diving -- hence the use of helium for the really really =deep dives. If oxygen at high pressures DIDN'T cause the bad effects, why bother mixing it with helium? Yes, nitrogen has narcotic effects at high pressure, but so does oxygen. -------------------------------------------------------------------------------- Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL Disclaimer: Hey, I understand VAXen and VMS. That's what I get paid for. My understanding of astronomy is purely at the amateur level (or below). So unless what I'm saying is directly related to VAX/VMS, don't hold me or my organization responsible for it. If it IS related to VAX/VMS, you can try to hold me responsible for it, but my organization had nothing to do with it. ------------------------------ Date: Wed, 11 Nov 1992 18:46:37 GMT From: "Thomas E. Smith [LORAL]" Subject: Lunar "colony" reality check Newsgroups: sci.space,alt.sci.planetary >> >> This is true for the most part, but at high O2 pressure, normally inflammable >> objects burn quite well. So in that respect, it is indirectly a fire >> hazard...sort of. :) >> > >Actually, normally inflammable objects burn quite well at sea-level pressure >of pure *air*. However, you need the high pressure to get normally >*non*flammable objects to burn. [high pressure O2] This is alt.sci.planetary isn't it? ------------------------------ Date: Wed, 11 Nov 92 16:36:43 GMT From: "John P. Mechalas" Subject: Lunar "colony" reality check and Apollo fire Newsgroups: sci.space,alt.sci.planetary In article <11NOV199208300719@vx.cis.umn.edu> soc1070 writes: >> The fire ignited the velcro under high-pressure, and the resultant toxic >>fumes killed the astronauts within seconds. > >I beg to differ. It was in fact Apollo 1, as many have pointed out. If you >check your Apollo history, you will see that 8 circled the moon, 9 did >LEO tests, 10 tested the LM in lunar orbit, 11 landed, 12 landed next to >the Surveyor, 13 blew an oxygen tank on the way to the moon, etc. You are right, of course... Rechecking my refs., I should have said "Spacecraft 12" and not "Apollo 12". Damn naming conventions. :) Apollo 1 was the mission number, and Spacecraft 12 was the spacecraft name...Pardon my confusion. >Secondly, the cause of the fire was never traced to any specific source. >According to Micheal Collens in _Carrying The Fire_, the inside of the >craft was so fried that a single cause could not be found; rather there >were several *probable* causes that resulted in an almost complete redesign >of the inside of the capsule. Correct. >You were right that almost anything will burn at 16psi pure O2, even >stainless steel. Unfortunatly for Grissom, White, and Chaffee, they didn't >die of toxic fumes. It was the fire that did them. I beg to differ on this point. The burns weren't fatal. The astronauts had suffocated. The velcro and nylon netting in the spacecraft burned very *very* rapidly under 16psi of pure O2( later tests showed that the velcro burned at a rate of almost 3 inches per second), and filled the entire cabin with gas. The fire itself was very selective...a flight manual inside the craft (where White was located) was almost untouched. -- John Mechalas "I'm not an actor, but mechalas@gn.ecn.purdue.edu I play one on TV." Aero Engineering, Purdue University #include disclaimer.h ------------------------------ Date: 11 Nov 92 18:30:34 GMT From: Henry Spencer Subject: Lunar "colony" reality check and Apollo fire Newsgroups: sci.space In article <1992Nov11.163643.20662@gn.ecn.purdue.edu> mechalas@gn.ecn.purdue.edu (John P. Mechalas) writes: >You are right, of course... Rechecking my refs., I should have said >"Spacecraft 12" and not "Apollo 12". Damn naming conventions. :) >Apollo 1 was the mission number, and Spacecraft 12 was the spacecraft >name...Pardon my confusion. Actually, the mission code at the time of the fire was AS-204, aka Apollo 204. There was no official name; the astronauts were calling it Apollo 1 but the booster people were calling it Apollo 4 (since three unmanned tests had preceded it), and NASA HQ had not issued a decision. The astronauts' wishes were complied with posthumously, at the request of their widows, and the Apollo 1 name was made official. -- MS-DOS is the OS/360 of the 1980s. | Henry Spencer @ U of Toronto Zoology -Hal W. Hardenbergh (1985)| henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 11 Nov 92 17:24:10 GMT From: Steve Jenkins Subject: Man in space... Newsgroups: sci.space In article roberts@cmr.ncsl.nist.gov (John Roberts) writes: >The world record for voluntarily remaining underwater (and conscious) is >something like 13 minutes. The fellow hyperventilated pure (1 Atm) oxygen >(don't try this at home!) ahead of time. Does this fit in with your model? >(I realize his lungs weren't exposed to vacuum, but he didn't have any way >of getting more oxygen except perhaps very slow diffusion from the water.) First of all, it's not *my* model, it's standard first-year med school physiology. So none of this should be controversial. :-) I'm assuming you haven't yet seen my reply to Henry, so I'll try not to repeat too much. It's well known that hyperventilation can extend the limit of voluntary breathholding. It's also well known that this is extremely dangerous. Last night I was checking up on myself by reading some reference material (I was right :->) and found a couple of good paragraphs about this. I'll type them in tonight. Now, hyperventilation doesn't add any appreciable amount to the stores of oxygen outside the lung, but it does reduce the CO2 stimulus to breathe. Holding a big breath of O2, however, provides at least 5 liters of O2. Normal resting O2 consumption is about 250 ml/min, so 5 l gives you plenty of O2 to hold your breath for 13 minutes. The point of all this is that breath-holding is not a good model for depressurization. When you hold your breath, you have a few minutes's worth of O2 in the lungs so you can maintain arterial oxygen partial pressure. In zero ambient pressure, your arterial PO2 will be zero, and it's lights out. >What's the mechanism by which the hemoglobin gives up its oxygen where >it's needed? And is there a 100% oxygen turnover on each pass of the >blood through the lungs? Oxygen moves from the lungs into arterial blood purely by diffusion--it moves from a region of higher to lower PO2. The magic of hemoglobin is that it binds O2 such that the PO2 on the blood side rises more slowly than the O2 content. (If O2 were merely dissolved in blood, the relationship would be linear.) The consequence is that more O2 can be loaded into the blood before partial pressure equilibrium is reached. (In normal humans equilibrium is always reached before a red blood cell leaves the lung.) At the tissues, the reverse process occurs. The tissue PO2 is lower than the blood, so O2 diffuses into the tissue. This time, hemoglobin holds the PO2 "artificially" high so that more O2 unloads before equilibrium. There are also secondary effects, in which the low arterial PCO2 assists O2 loading into blood, and the higher tissue PCO2 assists unloading O2 into tissue. O2 and CO2 have this mutual relationship; one is called the Bohr effect, the other is the Haldane effect. pH also shifts the dissociation curve. The PO2 of mixed venous blood is about 40 mmHg, so there is not complete unloading in the tissues. However, as O2 delivery to tissue is by diffusion, the low partial pressure prevents effective uptake. This is especially problematic in the brain, whose O2 demands are very high. >People seem to do "reasonably" well breathing air at around half normal >pressure, which would imply an oxygen partial pressure of 80mm Hg or not >much over. What's the lowest pressure of pure oxygen that people can >manage on? And what is the air pressure on the top of Mt. Everest? (It >has been climbed (strenuous physical activity) without supplementary >oxygen. It's very dangerous, but it has been done.) I don't believe the limits are well understood. *Slow* adaptation to low PO2 allows certain compensatory mechanisms (in particular renal adjustment of bicarbonate and left shifts in the hemoglobin dissociation curve). If you were to helicopter directly from sea level to Everest, you'd be unconscious long before the summit. On the other hand, it's clearly possible to ascend it one step at a time without supplementary oxygen. There is evidence to indicate that such feats engender brain damage. A standing joke among climbers is that you'd have to be brain-damaged to climb Everest anyway, so what the hell! >There's an article in a recent Scientific American on altitude sickness - >I haven't had time to more than scan it. Apparently it's not really healthful >to breathe air at any pressure noticeably less than sea level pressure, and >some people are much more susceptible than others to altitude-related >health problems. We're getting a little beyond my knowledge here. Altitude sickness is a complex of phenomena, at least some of which is related to low PO2, not merely low ambient pressure. It's certainly true that there is wide individual variation in response to altitude, and no good predictors of response that I'm aware of. -- Steve Jenkins jenkins@devvax.jpl.nasa.gov Caltech/Jet Propulsion Laboratory (818) 306-6438 ------------------------------ Date: Wed, 11 Nov 1992 15:50:04 -0500 From: Lawrence Curcio Subject: Man in the loop Newsgroups: sci.space Well it's strange, ain't it. Whenever there's a slow decision to be made, the responsibility in a human-machine system is given to the human, figuring the machine will make a mistake. (That's why we have decision *support* systems instead of decision *making* systems.) Whenever there's a fast decision to be made, as in fly-by-wire and nuclear power plant control, the responsibility is given to the machine, figuring the human will make a mistake. It's true that the human is always given the last word, but then if you look at nuclear power plant accidents, they seem to occur most when the human intervenes. Bottom line: Never trust a human, and never trust a machine. ------------------------------ Date: Wed, 11 Nov 1992 17:01:30 GMT From: "I am a terminator." Subject: NASA is too big Newsgroups: sci.space I was reading Feynman's account of his work investigating the Challenger and he was complaining about how NASA is so backward. Now the shuttles are flying again, what is NASA's situation? Henry Choy choy@cs.usask.ca ------------------------------ Date: Wed, 11 Nov 1992 13:54:43 -0500 From: Kevin William Ryan Subject: O2 spacecraft (was Re: Lunar "colony" reality check) Newsgroups: alt.sci.planetary,sci.space roelle@uars_mag.jhuapl.edu (Curtis Roelle) >>Suffice it to say that Mercury, Gemini, and Apollo astronauts worked in a >>5 psi pure O2 environment. This simplified the environmental control system >>and eliminated the need to purge N2 prior to EVA. > >Are you certain that Apollo astronauts breathed pure O2? I thought that >after the fatal Apollo 1 fire, which killed astronauts Grissom, White, and >Chaffee on January 27, 1967, pure O2 was no longer used because it was a >proven fire hazard. Or did NASA simply reduce the cabin pressure as >suggested by Carl Lydick? People can withstand a long term pure O2 environment, as long as the O2 pressure is on the order of the partial pressure of O2 in standard air. Since oxygen is about 20% of the atmosphere, about 3psi of oxygen would suffice. Somewhat higher pressure (the 5psi referred to) would be preferable simply for reasons of sound and temperature conduction. 15psi of oxygen is manageble for a time but not a good idea for the long run, due to problems with flammability, and I believe to problems related to hyperventilating (I could be wrong on the last point). The fatal Apollo fire happened with 15psi oxygen in the cabin during a ground test. That was an intermediate step leading to 5psi oxygen for orbital conditions, where the standard atmosphere was flushed. Following this the flushdown procedure was changed, as well as the Apollo hatch. The original hatch design sealed under positive pressure and opened inward: the new design, although heavier, opened owtward and therefore could be opened under a high internal pressure, such as that caused by a fire. The cabin atmosphere expansion of the fire effectively sealed the cabin until far too late for the crew. Incidentally, a number of the spacesuit designs have specified internal pressures on the order of 3psi in order to simplify design, including the Space Activity Suit of the early 70's, which was basically a multilayer leotard with a air tight neck seal. The air bag for the head and chest was at 200 torr (760 torr in one atmosphere) with pressure tapering to ~150 torr at the extremities, supplied by the stretch of the suit. (Sorry, pet project of mine, had to throw it in...) kwr Internet: kr0u+@andrew.cmu.edu ------------------------------ Date: Wed, 11 Nov 1992 17:06:02 GMT From: "Phil G. Fraering" Subject: Obscure Help Needed Newsgroups: sci.space In article <1992Nov11.013658.6395@julian.uwo.ca> jdnicoll@prism.ccs.uwo.ca (James Davis Nicoll) writes: An embarrassing request: my HP died and I discover I cannot remember how to do logs with a slide-rule, nor can I find my sr-related texts. Clearly, I am senile. Anyone out there recall how the damn things work? Hell, I would like to find out where to get a slide rule for when my calculator breaks... -- Phil Fraering In the country of the blind.... 60 minutes doesn't run stories about people trying to ban hearing implants! ------------------------------ Date: 11 Nov 1992 17:07:10 GMT From: "David M. Palmer" Subject: Obscure Help Needed Newsgroups: sci.space jdnicoll@prism.ccs.uwo.ca (James Davis Nicoll) writes: > An embarrassing request: my HP died and I discover I cannot >remember how to do logs with a slide-rule, nor can I find my sr-related >texts. Clearly, I am senile. Anyone out there recall how the damn things >work? > James Nicoll Sorry to post this to the net, but mail to jdnicoll@prism.ccs.uwo.ca bounces. Look for linear scales. The linear scale which goes from 0 to 1.0 is your base-10 log scale: put the cursor on the number you want the log of on the "A" scale, and read off the mantissa(? the fractional part of the log) on the linear scale. The characteristic(? the integer part) you get trivally by remembering where your decimal point is. For natural logs, there is a stack of linear scales, one for each of a range of decades. Hope this helps. If all else fails, you can use tables, or see if you can figure it out on an abacus. There may be computers on the net which can calculate logs as well. Followups to comp.sys.super, expecially if you are going to talk about logs in ARBITRARY BASES!!! (it's possible). -- David Palmer palmer@alumni.caltech.edu ------------------------------ Date: 11 Nov 92 17:28:31 GMT From: James Davis Nicoll Subject: Obscure Help Needed Newsgroups: sci.space In article <1992Nov11.152829.25858@pixel.kodak.com> dj@ekcolor.ssd.kodak.com (Dave Jones) writes: >James Davis Nicoll (jdnicoll@prism.ccs.uwo.ca) displaying brain-death wrote: >> >> An embarrassing request: my HP died and I discover I cannot >> remember how to do logs with a slide-rule, nor can I find my sr-related >> texts. Clearly, I am senile. Anyone out there recall how the damn things >> work? >> >You're serious, right? I mean praying to the netgods is easier than dashing >down to the university bookstore with a $10 bill in hand? OK, maybe you'd >need $20 for a calculator these days. > Advice for the slide-rule-challenged deleted Yes, it was a stupid request. At least I didn't ask for the time... I still find it hard to believe that I could so completely forget a skill I used every day not so long ago. It's also hard to believe no book store seems to stock books on the subject anymore. Are there no slide-rule makers left? At least sliderules never run out of power, nor do they suddenly decide to display '0.00' only, just when the user is calculating mass ratios. >Now when is my 1965 Faber-Castell going to become a collectors' item? I think it may be already... James Nicoll ------------------------------ Date: Wed, 11 Nov 1992 16:59:16 GMT From: Pat Subject: oxygen atmospheres Newsgroups: sci.space In article roberts@cmr.ncsl.nist.gov (John Roberts) writes: > >-From: henry@zoo.toronto.edu (Henry Spencer) >-Subject: oxygen atmospheres >-Date: 10 Nov 92 21:29:43 GMT > >-Neither. In space, the Apollo spacecraft used the atmosphere it was >-designed for: low-pressure pure oxygen. It wasn't feasible to run that >-way on the pad, though, because the spacecraft wasn't built to stand an >-external pressure exceeding internal pressure. After some attempts to >-fireproof the interior for 1atm of oxygen -- abandoned as impossibly >-difficult -- they switched to using a mixed-gas atmosphere before and >-during launch, with switchover to low-pressure pure oxygen on the way up. > Why didn't the SHuttle do this? i would have thought following apollo's lead, of reducing cabin pressure and going to pure O2, you could reduce the difficulty of EVA which is a primary shuttle mission. what win do they get out of having a 1 atm cabin at 80/20 N2/O2? ------------------------------ Date: Thu, 12 Nov 1992 01:08:36 GMT From: Ron Baalke Subject: Pioneer 6 Update - 11/11/92 Newsgroups: sci.space,sci.astro PIONEER 6 STATUS REPORT November 11, 1992 Yesterday, the Deep Space Network's 70 meter antenna in Goldstone, California supported a tracking pass of the Pioneer 6 spacecraft. Receiver lock was attained, but we were unable to attain telemetry lock because no subcarrier was detected. The expected bit rate was 16 bps uncoded telemetry. The AGC (Automatic Gain Control) was initially at -175.3 dbm, but was seen to fluctuate causing the receiver to toggle in and out-of-lock. The problem is under investigation. Pioneer 6 was launched on December 16, 1965 and is the oldest surviving spacecraft. Pioneer 6 was last supported on December 16, 1990, on the 25th anniversary of its launch, and no problems were encountered then. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | Give people a second /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | chance, but not a third. |_____|/ |_|/ |_____|/ | ------------------------------ Date: Tuesday, 10 Nov 1992 10:46:23 CET From: K3032E0@ALIJKU11.BITNET Subject: Sikhote-Aline-Meteorite (was Re: "Earth Gains a Retinue of Mini-Ast.") Newsgroups: sci.astro,sci.space I suppose Sikhote-Aline was the largest space-rock ever OBSERVED to come down Although it had probably around 200t before it entered the atmosphere, "only" 23t were collected. (By the way, 47 grams finally landed in my home...) Sure enough, thousands of small pieces (less than a few grams) and probably some large masses were not found in the dense forest, bringing the total weight well up to 50t. But Sikhote-Aline is NOT a Stony-Iron-Meteorite: It's a iron-meteorite (coarsest Octahedrite, chemical group IIB). Keep looking up| Herbert ------------------------------ Date: Wed, 11 Nov 92 14:06:22 GMT From: Daniel Briggs Subject: The Big Picture Newsgroups: sci.space In article <1041@dgaust.dg.oz> young@wattle.dg.oz (Philip Young) writes: >Given our propensity to fling hardware into the heavens, and our desire >to get a good handle on what's very old and far away, has anybody done >any serious investigation of the possibility of tacking astronomical eyes >on craft headed for interstellar space which would be suitable for >verrrrrrrrrrrry long baseline interferometry? We're not just talking >Earth orbit here. Seems to me we have the clocks, the computers, the >comms. What would be the shortest frequency we could realistically >deal with? Could costs be contained with a standardized, shrink-wrapped >observatory package? What might we discover with a (radio?) telescope >whose effective diameter increases 10E+4 km/sec or more for the forseeable >future? Well, I don't know of any serious investigation into this, but I can think of at least a few problems that are going to be very tough to beat. Basically, sensitivity is going to be the limiting factor. First of all, the existing space VLBI projects are designed around 10m class antennas, and they are none too sensitive. With antenna, receivers, electronics and maybe a maser, you're talking about a full sized mission right there. It's not anything you're going to tack onto a mission that happens to be going in that direction. (If you want to timeshare the main antenna between earth communications and observing, you'll need an onboard maser and a very high density tape recorder to record the astronomical signals. If you send up the "local" oscillator from earth, you'll need two big antennas on the spacecraft.) And of course, there's the question of bandwidth on the comm link, never mind the LO. Normal earthbound VLBI stations typically record the order of hundreds of kilobits per second or more, and it's this bandwidth that is typically the limiting factor in such systems. This isn't the sort of data you're going to send over a 300 baud link to a Voyager style spacecraft out beyond Pluto. There's also the fact that we don't know that there is going to be anything to see on au scale baselines. Essentially, interferometers are blind to emission distributed on a scale larger than lambda/baseline. So as the baseline gets longer, more and more of the flux resolves out. One of the OVLBI missions currently in the works plans to extend the orbit to 10 earth radii. It may or may not see anything on those size scales, assuming that it ever flies in the first place. Multiple au baselines are definitely dicey! Finally, you'll eventually run up against scattering disk caused by propagation thought the interstellar medium. It's a direct analog to visual seeing. We can already see this effect looking at maser spots towards the Galactic center. Out of the plane of the galaxy the FWHM of the seeing disk is .0015 l^2 / sqrt(|sin(b)|) milliarcseconds, where l is the wavelength in cm, and b is the galactic latitude. At the longer wavelengths, the existing OVLBI missions will be flirting with these limits. At 100 GHz, which is fairly tough even from the ground at the moment, you're limited to about 1 microarcsecond, which is only a baseline of .003 au, or 80 earth radii. So depressing as the thought may be, we couldn't even begin to mount an au scale VLBI mission at the moment, and if we could, it wouldn't tell us a whole lot since we can't see through the ISM. -- | Daniel Briggs (dbriggs@nrao.edu) | USPA B-14993 | New Mexico Tech / National Radio Astronomy Observatory | DoD #387 | P.O. Box O / Socorro, NM 87801 (505) 835-7391 | Support the League for Programming Freedom (info from lpf@uunet.uu.net) ------------------------------ Date: Wed, 11 Nov 1992 17:53:36 GMT From: "I am a terminator." Subject: What kind of computers are in the shuttle? Newsgroups: sci.space The computers used to control the shuttle use very complex programs that people don't want to rewrite for newer computers. Has any upgrades been done or are the computers still the same old beasts? Henry Choy choy@cs.usask.ca ------------------------------ Date: Wed, 11 Nov 1992 17:38:58 GMT From: mbobrowsky@scivax.stsci.edu Subject: Where are Pioneer and Voyager Headed? Newsgroups: sci.space A student asked me what direction the Pioneer and Voyager spacecraft are headed. I had no idea but I said I'd try to find out. Does anyone have an approximate RA and Dec for the asymptote of the trajectories of any of the four spacecraft that are beyond Pluto's orbit? Thank you, Matt ------------------------------ End of Space Digest Volume 15 : Issue 412 ------------------------------