X-Andrew-Authenticated-As: 32766 Return-path: 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 ; Sun, 21 Oct 1990 02:46:53 -0400 (EDT) Message-ID: Precedence: junk Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sun, 21 Oct 1990 02:46:22 -0400 (EDT) Subject: SPACE Digest V12 #476 SPACE Digest Volume 12 : Issue 476 Today's Topics: Re: Deep Lunar Dust Story? Re: Theories needed on life Deep Lunar Dust Story? Re: SPACE Digest V12 #464 Ulysses Update #2 - 10/19/90 Re: Theories needed on life Re: Venus/Magellan, poles Administrivia: Submissions to the SPACE Digest/sci.space should be mailed to space+@andrew.cmu.edu. Other mail, esp. [un]subscription notices, should be sent to space-request+@andrew.cmu.edu, or, if urgent, to tm2b+@andrew.cmu.edu ---------------------------------------------------------------------- Date: 19 Oct 90 15:19:06 GMT From: ubc-cs!news-server.csri.toronto.edu!utgpu!utzoo!henry@beaver.cs.washington.edu (Henry Spencer) Subject: Re: Deep Lunar Dust Story? In article <60200@bbn.BBN.COM> ncramer@labs-n.bbn.com (Nichael Cramer) writes: > ... Actually, Australian radio physicists, > working on 24,000 Mc/s, have already got about a meter inside the Moon! > They have shown that the dust layer is probably only about 1mm thick, > with solid rock underneath... And of course, they were wrong, since the lunar regolith is quite a bit more than 1mm thick. Solid rock is a long way down; the surface layer has been churned to dust and fragments by meteorite bombardment. -- The type syntax for C is essentially | Henry Spencer at U of Toronto Zoology unparsable. --Rob Pike | henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: 20 Oct 90 15:58:41 GMT From: usc!cs.utexas.edu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!physics.utoronto.ca!neufeld@ucsd.edu (Christopher Neufeld) Subject: Re: Theories needed on life In article <10168@ubc-cs.UUCP> mgobbi@cs.ubc.ca (Mike Gobbi) writes: > >A planet 3 or 4 times the size of earth? Do you mean 3xmass or 3xradius? > >In the former case, I suspect that the life forms would have short thick >legs, and would be unlikely to be humanoid. Far more likely, they would have >four or more legs to distribute their mass. > >In the latter case, we are talking about a 27-G planet! > Not at all! If we assume that the mean density remains constant, tripling the radius triples the surface gravity. Tripling the mass raises the surface gravity by a factor of 3^(1/3) which is roughly a 44% increase. I don't see that a 44% higher gravity is completely outside the realm of humanoid shape. Birds might be a bit huskier, though :-) -- Christopher Neufeld....Just a graduate student | "The pizza was just a neufeld@helios.physics.utoronto.ca Ad astra! | detonator; I mean, if cneufeld@{pnet91,pro-micol}.cts.com | it had set off the "Don't edit reality for the sake of simplicity" | hams...." Downtown Brown ------------------------------ Date: 19 Oct 90 07:55:30 GMT From: bbn.com!ncramer@apple.com (Nichael Cramer) Subject: Deep Lunar Dust Story? A couple of weeks back on Sci.Physics someone [sorry, can't seem to find the original posting] recounted the "NASA was concerned that the lunar-lander might sink in the deep moondust" story. On the other hand, I recently came across the following (in _Astounding Days_, the second volume of Arthur C. Clarke's "autobiography"). It is from a letter by ACC that was published in in the Dec 1950 issue of "Astounding": "[Clarke is commenting on an article in which] Whitton remarks, re the lunar dust layer, 'Our experimental limitations keep us, of course, from probing farther beneath.' Actually, Australian radio physicists, working on 24,000 Mc/s, have already got about a meter inside the Moon! They have shown that the dust layer is probably only about 1mm thick, with solid rock underneath. For full details, see 'Microwave Thermal Radiation From the Moon,' J. H. Piddington and H. C. Minnett (Aus. J. Sci. Res. 2, 63-77 -- March 1949)." (Now, obviously "Astounding" is not the journal of choice in these matters, but while ACC may not be a true expert on these things, he is usually quite well-informed and does cite what appears to be a credible source.) So my question --preferably to someone who was on the scene: Was this (the possible sinking in lunar dust) a real concern? If it wasn't, is this just another NASA- related urban legend? If it was, why was there still concern ~two decades after the issue was apparently resolved? N P.S. BTW, I hope it's clear this not meant in any way as a flame; just trying to resolve an apparent contradiction. -- N Note follow-ups. ------------------------------ Date: Fri, 19 Oct 90 15:32:09 CDT From: David Smith Subject: Re: SPACE Digest V12 #464 please unsub. me from this list, it is very interesting, but I no longer have the time to read these, thank you for this list and the info though. David Smith TCDS000 at TCSVM or at VM.TCS.Tulane.Edu ------------------------------ Date: 19 Oct 90 23:44:34 GMT From: sdd.hp.com!uakari.primate.wisc.edu!abcfd20.larc.nasa.gov!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov!baalke@ucsd.edu (Ron Baalke) Subject: Ulysses Update #2 - 10/19/90 Ulysses Mission Status October 19, 1990 The Ulysses spacecraft is now 7,172,766 miles (11,543,435 km) from Earth and 498,753,202 miles (802,665,473 km) from Jupiter. It is traveling 91,503 mph (147,261 kph) relative to the Sun, and 24,752 mph (39,834 kph) relative to the Earth. The first TCM (Trajectory Correction Maneuver) was successfully completed on the October 18. Detailed evaluation of the resulting change in trajectory has commenced. The spin rate was adjusted to 5 rpm after the completion of TCM-1. The purpose of the radial manuever of TCM-1 was to correct the direction of track of the initial trajectory. Radial thrusters on the spacecraft were activated in pulsed mode for a period of twenty three hours. Intermediate spin rate corrections were made to maintain the spin rate of the spacecraft within pre-determined limits around 5 rpm. The cross coupling effects which cause a change to the spin rate during the radial thrusters firing was less than predicted and this therefore led to a reduction in the overall duration of the radial burn. The purpose of axial maneuver of TCM-1 was to increase the velocity of the spacecraft along the direction of track. Axial thrusters were activated for a total of about one hour, the burns being split into two separate manuevers. The first longer manuever was interrupted on-board forty seconds after commencement due to a higher than expected spin rate change caused on-board protection logic criteria to be exceeded. The AOCS (Attitude and Orbit Control Subsystem) was configured for on-board spin rate control during the manuever and was re-started. The manuever was completed without incident. KEP (Energetic Particle and Interstellar Neutral Gas) experiment switch-on and GAS (Neutral Gas experiment) cover release commands were uplinked to the spacecraft as time-tagged commands for execution on October 19. The initial switch-on will be almost immediately followed by the release of all protective experiment covers (with the exception of the LAN experiment). The LAN experiment measures low energy charged particles. The LAN cover will not be released until the TCM-2 has been completed. Thermal reconfigurations have been carried out to maintain the desired thermal environment. A special thermal reconfiguration was utilized during the first TCM to maintain the thruster block temperatures within limits. ___ _____ ___ /_ /| /____/ \ /_ /| | | | | __ \ /| | | | Ron Baalke | baalke@mars.jpl.nasa.gov ___| | | | |__) |/ | | |___ Jet Propulsion Lab | baalke@jems.jpl.nasa.gov /___| | | | ___/ | |/__ /| M/S 301-355 | |_____|/ |_|/ |_____|/ Pasadena, CA 91109 | ------------------------------ Date: 20 Oct 90 17:53:10 GMT From: bu.edu!slehar@EDDIE.MIT.EDU (Steve Lehar) Subject: Re: Theories needed on life joe@hanauma.stanford.edu (Joe Dellinger) states: Joe | Joe | All the animals we normally think of, things like lizards, Joe | bears, dogs, whales, horses, people, monkeys, snakes etc, are Joe | variations on a remarkably consistent theme. A backbone with Joe | vertebrae, 4 limbs, five digits per limb, one head, one tail, Joe | etc etc. Joe | . Joe | . Joe | . Joe | It's just far faster for evolution to keep ringing variations on Joe | the old themes as needed than it is to invent something new from Joe | scratch. New inventions don't stand a chance competing against Joe | the old established monopolies. Joe | Recent studies in reaction-diffusion theory reveal some interesting phenomena in morphogenesis. It seems that morphogenic substances in the early embryo (at the blastula stage, where there is essentially just a lump of uniform cells) participate in resonating chemical feedback reactions- with two morphogens catalysing the formation or destruction of themselves or each other. The result is stable spatial patterns of chemical concentrations, that 'resonate' in the 'cavity' (body mass) of the embryo creating patterns very like the vibration patterns of a drum or tuning fork. This mechanism is very different from passive diffusion of a morphogen through a tissue, because the patterns depend very much on the shape and volume of the tissue. (Welsh et al. [1] illustrates this phenomenon with spatial patterns of concentration in a test tube of originally uniform composition) Consider the case of the hydra- you cut it in half, and the bottom half develops tentacles at the severed end, while the top half develops a foot. This occurs regardless of where you bisect the creature. Passive diffusion of morphogens cannot explain such phenomena, but the reaction diffusion model can. Where this bears on the argument about the shapes of life forms is that there are certain types of patterns that morphogens can form. For instance, James Murray [2] shows that spots, stripes and other markings on animals always follow certain patterns- since they are produced by the same diffusion reaction mechanism- the difference in the patterns being a result of the geometry of the embryo at the time that the pigmented cells are determined. For instance, all spotted animals get rings at the tapered tips of their tails- and yet no striped animal ever has spots on their tail. Similar morphogenic reactions in effect in the early embryo determine the fundamental morphology of the creature. In particular, repeated segmentation of the body plan is as natural as rings on a tail. This explains why such diverse creatures as humans and insects have a fundamentally segmented architecture. Here is another interesting model put forward by Newman & Frisch [3] to explain the differentiation of the limb bud tissue in a chick embryo into muscle and bone progenitors. It seems that a reaction diffusion resonance takes place in the tip of the limb bud, where the resonant patterns change as the limb bud grows. The initial pattern has a one striped resonance, which then becomes a two striped and finally a three striped pattern as the resonant 'cavity' expands. All this time, the tip of the limb bud is growing outwards, so it 'leaves behind' first a single, then a double and finally a triple trail of bone progenitor. STAGE 1 STAGE 2 STAGE 3 ff ffff ffffff BB ffBB ffffBB ff BBff ffBBff ffBB BBffBB <-proximal ffff ffBBff distal-> ffffBB ^ ffffff f = flesh | ^ B = bone | | | | Growth AND chemical resonance only occurs in the tip of the limb bud- i.e. the right hand column in this figure. The tip grows left to right, leaving behind a limb, and the limb expands in size the whole time. This explains why the chick has three toes, two distal leg bones (radius and ulna) and one proximal leg bone (femur). What is significant about this model is that it suggests that the pattern of fewer bones proximally to many bones distally is a fundamental property of diffusion reaction in a growing limb bud, and might well appear in alien life forms as well. This is not to refute Joe Dellinger's statement that it is easier for nature to adapt an old life form to a new environment than to start from scratch, but simply to say that a lot of the apparantly arbitrary choices made by nature along the way (such as why we have a segmented body plan, or why we have one bone in the upper leg and two in the lower leg) may not have been as arbitrary as they first seemed. [1] Welsh, B., Gomatam, J., & Burgess, A. (1983) Three Dimensional Chemical Waves in the Belousov-Zhabotinskii Reaction. NATURE Vol. 304 611-614 [2] Murray, J. (1988) How The Leopard Gets Its Spots. SCIENTIFIC AMERICAN, March 1988 Volume 258 Number 3 [3] Newman S. & Frisch H. (1979) Dynamics of Skeletal Pattern Formation in Developing Chick Limb. SCIENCE VOL 205, 662-668 -- (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O) (O)((O))((( slehar@park.bu.edu )))((O))(O) (O)((O))((( Steve Lehar Boston University Boston MA )))((O))(O) (O)((O))((( (617) 424-7035 (H) (617) 353-6741 (W) )))((O))(O) (O)((O))(((O)))((((O))))(((((O)))))(((((O)))))((((O))))(((O)))((O))(O) ------------------------------ Date: 19 Oct 90 03:49:07 GMT From: usc!samsung!munnari.oz.au!metro!cluster!minnie!paulod@ucsd.edu (Paul O'Donnell) Subject: Re: Venus/Magellan, poles In article <1990Oct17.170350.27044@jato.jpl.nasa.gov> baalke@mars.UUCP (Ron Baalke) writes: >In article <901017.113902.EDT.JEFF@UTCVM> JEFF@UTCVM.BITNET (Jeffrey R Kell) writes: >>spin, etc., but to ask a possibly silly question, HOW do you determine >>where a longitude grid BEGINS? Find Greenwich, Venus? ( ;-) ) >Ariadna Crater is used as the prime meridian on Venus. It is a small Yes, but is there a general rule for this or does someone need to specify a geographical point for each planet? Paul O'Donnell paulod@basser.cs.su.OZ.AU .signature: No such file or directory ------------------------------ End of SPACE Digest V12 #476 *******************