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 ; Fri, 23 Feb 90 01:26:42 -0500 (EST) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Fri, 23 Feb 90 01:26:19 -0500 (EST) Subject: SPACE Digest V11 #71 SPACE Digest Volume 11 : Issue 71 Today's Topics: Re: Spacecraft drives and fuel efficiency Re: Why we need Earth Re: Galileo Update - 02/16/90 Astronaut Mullane to retire from NASA, Air Force (Forwarded) Re: Why we would need a planet. Re: inter stellar travel Re: Approaching light speed in space travel Re: Spacecraft on Venus Re: Did SEASAT See More Than It Was Supposed To? Re: Fun Space Fact #1: Launcher Development Costs Re: Spacecraft on Venus ---------------------------------------------------------------------- Date: 20 Feb 90 18:17:42 GMT From: cs.utexas.edu!uwm.edu!ogicse!littlei!nosun!snidely@tut.cis.ohio-state.edu (David Schneider) Subject: Re: Spacecraft drives and fuel efficiency In article <1990Feb2.182755.20167@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >[...] Practical interstellar missions >need not only very high exhaust velocities, but also respectable acceleration, >otherwise the acceleration phase simply takes too long. Accelerating to >0.1c at 0.001G takes most of a century; a substantial fraction of one >gee is pretty much a requirement. [r-o-t: scale from c = 1G * 1 yr] >[...] >If you want really high exhaust velocities, antimatter is better. The >idea of antimatter rockets is now being taken very seriously. We >(probably) know how to make antihydrogen cheaply enough to make them viable. I'm desperately trying to remember the details, but I do recall an academic advisor (back when I was a physicist-to-be) showing me his back-of-the-envelope calculations that showed an matter-anitmatter reaction for 1G acceleration (producing gamma rays as a matter of efficiency) would fry the departure site. Take your pick of departure sites :-). Dave Schneider Tuesday, Feb 20 ------------------------------ Date: 21 Feb 90 22:11:00 GMT From: apollo!nelson_p@eddie.mit.edu (Peter Nelson) Subject: Re: Why we need Earth : paul dietz: :>Why? Planets are a terribly inefficient way to use mass. All that :>inaccessible matter just to provide gravity, when rotating structures :>(of sufficiently large size) would do just as well, using much :>less material. "It's people like you what cause unrest." Seriously, the Japanese are sending satellites to the moon and are seriously planning a space station. The Chinese, Japanese, Europeans, and Soviets are continuing to advance their commercial space programs. And the Americans have been debating the merits of a space station, manned Mars mission, return to the moon and a lot of other important questions FOR YEARS without making up their minds. Meanwhile the US lead in aerospace, once apparently invincible, evaporates daily. Fewer and fewer US children choose careers in science and engineering and many who do often graduate college with a similar level of preparation to a good high school student in some other countries. I CAN'T BELIEVE that space enthusiasts in the US would waste their time on silly debates about planet deconstruction. It reminds me of the frequent objectivist and libertarian lectures we used to see here about how they would spend their retirement years in the asteroid belts if only the government would conveniently get out of their way by vanishing! Dreamers!! Dreaming is good up to a point; it can provide motivation and interest. But American space enthusiasts spend too much time dreaming and thinking about far-off future things, and not enough time addressing the boring and dirty but neccessary tasks of building political consensus, reaching compromises with other space enthusiasts to present an effective united front, and addressing social, economic, and infrastructure problems which prevent more US space activity, in an *effective* manner. The pros and cons of planetary deconstruction are irrelevant because the way things are going, Americans won't be the ones to decide. ---Peter ------------------------------ Date: 22 Feb 90 14:29:26 GMT From: astroatc!nicmad!otto@speedy.wisc.edu (Douglas Otto) Subject: Re: Galileo Update - 02/16/90 In article #2876@jato.Jpl.Nasa.Gov> baalke@mars.jpl.nasa.gov (Ron Baalke) writes: # # GALILEO # MISSION STATUS REPORT # FEBRUARY 16, 1990 # #Since a single compressed #image being returned contains a little over 3 x 106 bits and the imaging data #is transmitted to Earth at 256 bits/sec. (imaging data portion of the 1.2 #kbps), the time to retrieve a picture from the telemetry standpoint only is #roughly 3.6 hours. This is odd since 3.6hr * 3600 sec/hr * 256 bits/sec = 3317760 bits = 3 x 1105920 bits per image! This is a "bit" larger than 3 x 106 bits. Don't these PR people check what they write? I know it's not your fault Ron. By the way, thanks to Ron for providing these reports so consistantly. -- UUCP:harvard-\ att--\ | Douglas Otto 608 271-3333 ext 2346 ucbvax!uwvax!astroatc!nicmad!otto | Nicolet Instrument Corp. rutgers--/ rolls--/ | 5225-1 Verona Rd ames--/ decvax-/ | Madison, Wis 53711-0508 ------------------------------ Date: 21 Feb 90 17:19:49 GMT From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov (Peter E. Yee) Subject: Astronaut Mullane to retire from NASA, Air Force (Forwarded) Ed Campion Headquarters, Washington, D.C, February 21, 1990 Jeff Carr Johnson Space Center, Houston RELEASE: 90-28 ASTRONAUT MULLANE TO RETIRE FROM NASA, AIR FORCE Effective July 1, 1990, Colonel Richard M. Mullane will retire from NASA and the Air Force. Mullane was selected as a mission specialist astronaut in 1978 and has flown two Space Shuttle missions. His third flight is scheduled for launch Thursday aboard Atlantis. He flew on Discovery's maiden flight, STS 41-D, in August 1984 and on the third flight of Atlantis, STS-27, in December 1988. After leaving NASA and the Air Force, Mullane will return to his hometown of Albuquerque, N.M. ------------------------------ Date: 21 Feb 90 18:07:15 GMT From: zaphod.mps.ohio-state.edu!samsung!aplcen!aplvax.jhuapl.edu!jwm@tut.cis.ohio-state.edu (Jim Meritt) Subject: Re: Why we would need a planet. Does a phrase containing the word "eggs" and the sub-phrase "one basket" ring a bell as to why we should disperse? That that is is that that is. That that is not is that that is not. That that is is not that that is not. That that is not is not that that is. And that includes these opinions, which are solely mine! jwm@aplvax.jhuapl.edu - or - jwm@aplvax.uucp - or - meritt%aplvm.BITNET ------------------------------ Date: 21 Feb 90 18:41:07 GMT From: zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!aplcen!aplvax.jhuapl.edu!jwm@tut.cis.ohio-state.edu (Jim Meritt) Subject: Re: inter stellar travel In article <21016@watdragon.waterloo.edu> jdnicoll@watyew.waterloo.edu (Brian or James) writes: } Imagine Lebanon's civil war in a L-5 style community. Precisely! They screw up their own bubble without (accidently?) messing up everyone elses. Given a choice of sharing a closet or a continent with two guys fighting with gernades, I prefer to keep them away. That that is is that that is. That that is not is that that is not. That that is is not that that is not. That that is not is not that that is. And that includes these opinions, which are solely mine! jwm@aplvax.jhuapl.edu - or - jwm@aplvax.uucp - or - meritt%aplvm.BITNET ------------------------------ Date: 21 Feb 90 18:17:13 GMT From: cs.utexas.edu!asuvax!hrc!valley!pfluegerm@tut.cis.ohio-state.edu (Mike Pflueger) Subject: Re: Approaching light speed in space travel In article , GILL@QUCDNAST.BITNET writes: > Scott (scott@xcf.berkeley.edu) writes: > >There is yet another major problem ... with the relativistic time dialation, > > piloting a vessel safely at such speeds will become quite a pain. Not only > > will the computer become enormously slow at reacting to potential dangers, > > but these objects will be very difficult to detect due to high speed, large > > blueshift, and relativistic "tunnel vision". > It is hard to see what you mean here. The computer will not > slow down at all - at least not for those on the ship. However, one > does have to worry about light travel time. For example, consider a > ship travelling at 0.5c. It sends out a radar signal that reflects off > of an asteroid that is 1 ly in front of the ship the instant the signal > is sent out. By the time that the ship receives the reflection, 2/3 of > a ly will have been travelled already by the ship. There is some time > to react, but not overly much. At higher speeds, the available reaction ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Yeah, only 4 months... :-) Sounds like a modern version of the arguments people had about why we'd never travel faster than the speed of sound. Of course, I believe the speed of sound is more of a big hill than a boundary condition. -- Mike Pflueger @ AG Communication Systems (formerly GTE Comm. Sys.), Phoenix, AZ UUCP: {...!ames!ncar!noao!asuvax | uunet!hrc | att}!gtephx!pfluegerm Work: 602-582-7049 FAX: 602-581-4850 Packet: WD8KPZ @ W1FJI Internet: PLEASE USE UUCP PATH (NOT INTERNET)! ------------------------------ Date: 21 Feb 90 18:33:02 GMT From: rochester!dietz@PT.CS.CMU.EDU (Paul Dietz) Subject: Re: Spacecraft on Venus In article <1990Feb21.164544.9750@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >> What would it take - in terms of alloys, etc. - for a manned >> spacecraft to survive on the planet Venus? ... > >The chemical problems are manageable. The real problem is not alloys, >but building the most ferociously capable heat-pump system you ever saw, >to pump heat out faster than it can leak in. Not impossible, but a major >engineering challenge. May I suggest a simpler system: the vehicle has very good thermal insulation & heat sink, and uses a balloon to periodically lift itself into the (relatively cool) upper atmosphere, where heat is dumped more easily. So, what sort of balloon is necessary for lifting off Venus's surface? The gas there is about 55 times the density of earth air at sea level (it is hotter, but under much more pressure, and has a higher average molecular weight), so a small balloon should have great lifting power. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: 22 Feb 90 16:36:14 GMT From: samsung!cs.utexas.edu!jarvis.csri.toronto.edu!utgpu!utzoo!henry@think.com (Henry Spencer) Subject: Re: Did SEASAT See More Than It Was Supposed To? In article <4762@aplcen.apl.jhu.edu> jwm@aplvax.jhuapl.edu.UUCP (Jim Meritt) writes: >}Seasat radar images definitely showed detailed features of the sea bottom >}in shallow areas.... > >Henry, the shaping of the geoid (outlining the bottom contours on the >surface shape) has nothing to do with the depth. Works nicely everywhere. >Trenches look neat. However, I see no way for that mechanism to be used >to detect neutrally boyant objects. Sorry, Jim, I wasn't talking about the geoid image, neat though it is, but about bottom features visible on the high-resolution SAR images. To my recollection, this happened only in shallow areas, and the apparent resolution was quite high -- at least superficially too high for geoid effects to be responsible. -- "The N in NFS stands for Not, | Henry Spencer at U of Toronto Zoology or Need, or perhaps Nightmare"| uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: 22 Feb 90 17:09:00 GMT From: snorkelwacker!usc!cs.utexas.edu!jarvis.csri.toronto.edu!utgpu!utzoo!henry@bloom-beacon.mit.edu (Henry Spencer) Subject: Re: Fun Space Fact #1: Launcher Development Costs In article <2250@syma.sussex.ac.uk> nickw@syma.susx.ac.uk (Nick Watkins) writes: >>And are the ring-burning SRB's supposed to be considered as having >>'worked well' even though the few engineers who knew the whole >>disquieting truth beforehand cringed inwardly at every launch? > >See a recent issue of The Scientist (22 Jan 90) for the latest on Roger >Boisjoly, and the price he has paid. But before you weep too hard for him, read the Rogers Commission report, noticing what he did and didn't (mostly didn't) do at the time. He's gotten the shaft not for trying to stop the launch -- he didn't try hard -- but for talking too much to the investigators afterwards. -- "The N in NFS stands for Not, | Henry Spencer at U of Toronto Zoology or Need, or perhaps Nightmare"| uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ Date: 21 Feb 90 21:33:08 GMT From: hpda!hpcupt1!hpisod2!jem@ucbvax.Berkeley.EDU (Jim McCauley) Subject: Re: Spacecraft on Venus In a recent posting, klaes@wrksys.enet.dec.com writes: What would it take - in terms of alloys, etc. - for a manned spacecraft to survive on the planet Venus? Keep in mind that this world contains an atmosphere of carbon dioxide and sulfuric acid, an atmospheric pressure ninety times that of Earth, and a surface temperature capable of melting lead. No Soviet or American lander has yet survived longer than a few hours on this hellish planet. What would it take to keep such a craft functioning for days and weeks, even months? Would there be any way to construct a permanent base, keeping in mind that the Venusian climate cannot be changed any time soon. Larry Klaes ---------- Answer: Don't land. It would be a very interesting design exercise to create a craft that was designed to aerobrake into the atmosphere of Venus, deploy a flotation system and remain suspended in the upper regions of that atmosphere, where temperature, pressure and relative cloudlessness might afford better opportunities for human survival. Such a "Venusian dirigible" (or blimp) would be able to make sustained optical, radar and infrared observations of the surface and atmosphere, offering a valuable scientific platform. Also, since the thermal gradient of the Venusian atmosphere is (per unit of height) far greater than that of any other planet, there might be interesting opportunities for energy generation. Hot gases could be pumped from below (up a low-mass pipe) to a "cold" station where energy could be extracted from the heat difference. This energy might be exploited to "mine" the Venusian atmosphere for chemicals that might be of interest to a space-faring civilization. A centrifugal tether might be employed to fling the chemical products into space for outbound transport in exchange for inbound products and raw materials necessary for the maintenance of the floating station. It is also interesting to speculate what life might be like on such a station. I suspect that it would be rather like life on a submarine -- except for those strolls on the exterior catwalks, staring down at the lower cloud deck at the misty Hades below... then retreating back into the cramped interior of the station. Not the place for claustrophobes, acrophobes or agoraphobes! USO Jim McCauley USO GSY/USO/HP-UX Learning Products USO Learning Products Engineer USO General Systems Division USO Hewlett Packard Company USO XXX USOUSOUSO XXX XXX XXX XXX 19447 Pruneridge Avenue USO XXX USOUSOUSO XXX XXX XXX XXX Mail Stop 48SO USO XXX USO USO XXX XXX XXX XXX Cupertino CA 95014 USOUSOUSO USOUSOUSO XXX XXX XXX XXXXX USOUSOUSO USOUSOUSO XXX XXX XXX XXXXX (408) 447-4993 XXX XXX USO XXX XXX XXX XXX XXX XXX USO XXXXXXXXX XXX XXX jem@hpulpcu3.hp.com XXX XXX USO XXXXXXX XXX XXX ------------------------------ End of SPACE Digest V11 #71 *******************