Date: Fri, 28 May 93 10:48:20 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V16 #632 To: Space Digest Readers Precedence: bulk Space Digest Fri, 28 May 93 Volume 16 : Issue 632 Today's Topics: Adaptive Optics (was Space Marketing) August Meteor Shower May Threaten Earth Satellites (2 msgs) Hey Ken! You awake? You exist? (LEO Cost; Return cost) Magellan Update #3 - 05/25/93 Moon Base (3 msgs) Tom Wolfe's THE RIGHT STUFF - Truth or Fiction? Voyager Discovers the First Direct Evidence of the Heliopause Why a far side Science station. Why is everyone picking on Carl Sagan? 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: 24 May 93 17:38:02 GMT From: Dani Eder Subject: Adaptive Optics (was Space Marketing) Newsgroups: sci.astro,sci.space In article <1993May21.170848.18186@ucsu.Colorado.EDU> fcrary@ucsu.Colorado.EDU (Frank Crary) writes: > >Exactly how small? Unless I'm very much mistaken, it can't be arbitrarily >small and the size scales with the size of the primary. 5 - 10cm >is typical of the current ~1m telescopes, but wouldn't you need >something more like 50 cm for a 5-m primary? > > >Does this mean you can have an arbitrarily small mirror, so long as >you could also make the individual elements arbitrarily small? I'm >not sure how you could: Can you actuate a 2mm mirror accurately >enough. I assume the distance it would have to be moved would >similarly be scaled down. Does that mean it has to be accurately >moved distances on the order of a micron? > > >But how quickly can these hundreds of element arrays be adjusted? >The required time scale increases faster than linearly with >the observed frequency. All in all, I think my original remark >was reasonably accurate: Large (~5m) adaptive telescopes working >in the visible are still a long way away. > Last year I was involved with a NASA study on laser power beaming to orbiting spacecraft (I was working the spacecraft end). As a result, I got to sit in on presentations on the current state of the art in wavefront control. The coherence scale of the atmosphere is on the order of 6 cm on the ground. The deformable mirror can be any mirror in your optical train, but the preferred location is the last surface before your imaging electronics (CCD). This way you can not only adjust for atmospheric distortion, but also for any mechanical distortion caused by the primary and secondary mirrors due to temperature and gravity. The deformable mirror can be small, limited by diffraction onto your imaging electronics, and by the ability to fabricate small actuators. The NASA program was looking at hexagonal segments 2 cm across for the deformable mirror. Each segment has 3 peizo-electric acuators. Quartz has the property of changing shape under electric fields. A sufficiently long rod of quartz can provide the several tens of wavelengths of movement needed to handle the distortions. The positioning resolution acheived is about 4 nanometers, which gives a tilt resolution of .2 microradian for a 2cm segment (or 0.04 arc second). The 2 cm segment size was chosen for manufacturing reasons. The concept is to have a control chip for each segment mounted on the backplane, and driving the peizoelectric actuators. The segment is mounted on the front side, and the actuators are mounted to the back of the segment and to a structual backing. The whole mirror has to be driven at about 200Hz, since that is the characteristic time for the atmospheric distortions (it is a funtion of wind velocity in the atmosphere, and the turbulence it generates. The current limiting factor on the adaptived optics is the computer power to analyze the distorted guide star image and calculate how to command the mirror segments. For an 8m telescope with 0.1 arc second resolution, it would (in 1992) take 30 racks full of signal processing chips to do solutions at 200 Hz (those are 19 inch wide by 6 foot high racks). Where n is the number of segments, the processing to solve the distortion goes as n*ln(n), and n goes as diameter squared. Today, you can back down by restricting to a smaller mirror, or by not solving as fast, thus losing some resolution. But you can in the lab today show real performance gain in the visible for dozens to a few hundred elements, good for up to about a 1 meter telescope. Hopefully in a decade or two the cost of the processing chips will come down to where you can afford to drive a big telescope. Dani Eder -- Dani Eder/Meridian Investment Company/(205)464-2697(w)/232-7467(h)/ Rt.1, Box 188-2, Athens AL 35611/Location: 34deg 37' N 86deg 43' W +100m alt. ------------------------------ Date: 26 May 1993 15:38 UT From: Ron Baalke Subject: August Meteor Shower May Threaten Earth Satellites Newsgroups: sci.space >PRESS NOTICE FROM ROYAL ASTRONOMICAL SOCIETY >Over the last few years, meteor watchers have noticed an enhanced >activity peak in the Perseids lasting for about one hour. Material ejected >recently from the comet appears to be responsible. This year, the Earth >will cross the Perseid meteoroid stream behind the comet when it has not >long passed our way. Peter Brown noticed that the circumstances of this >encounter will be very similar to the ones that produced the spectacular >Leonid meteor storms of 1966 and 1833. Were any satellites affected by the meteor storm of 1966? ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | Never laugh at anyone's /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | dreams. |_____|/ |_|/ |_____|/ | ------------------------------ Date: Wed, 26 May 1993 15:59:16 GMT From: Dave Michelson Subject: August Meteor Shower May Threaten Earth Satellites Newsgroups: sci.space In article <26MAY199315383516@kelvin.jpl.nasa.gov> baalke@kelvin.jpl.nasa.gov (Ron Baalke) writes: > >Were any satellites affected by the meteor storm of 1966? It would be interesting to see the data from Pegasus during that period. (I assume they were still operating.) Does anyone have access and can they possibly post a summary? Pegasus was a Marshall satellite so would the data be archived there? I've never seen a NASA report on Pegasus; just popular accounts :-( -- Dave Michelson -- davem@ee.ubc.ca -- University of British Columbia ------------------------------ Date: 26 May 1993 12:06:52 -0400 From: Pat Subject: Hey Ken! You awake? You exist? (LEO Cost; Return cost) Newsgroups: sci.space In article <1tu2va$2ts@nml1sun.hsc.usc.edu> khayash@nml1sun.hsc.usc.edu (Ken Hayashida) writes: |unfamiliar with the technical demands of spaceflight. When you |over sell DC-Y/X/ SX-2, you do the samething that your predecessors |did for shuttle...over sell to the populous while understanding the |engineering limitations behind closed doors. Actually I see the DC, as being sold exactly right. They are listing exactly what criteria are needed to make it fly, where the risk items are, what their weight, time and service bdgets are and what their contingency plans are. DC-X cost 60 Million, maybe 10-15 more, if they have to build another flight test article, which i really think is a neccesity.IMO, If DC-X dramatically underperforms, they will apply these lessons to DC-Y. IF DC-Y, underperforms, they'll stop program until the probblems are fixed. If DC-X performs, and the follow-on vehicle underperforms, then they'll stop program until they have a fix, and go on with the DC-1. Shuttle would have been way ahead, if they had built a small scale vehicle to test critical technologies, of course, too small and it would have had real different problems, like the TPS would have to be even better. pat ------------------------------ Date: 26 May 1993 15:53 UT From: Ron Baalke Subject: Magellan Update #3 - 05/25/93 Newsgroups: sci.space,sci.astro,alt.sci.planetary Forwarded from Doug Griffith, Magellan Project Manager MAGELLAN STATUS REPORT May 25, 1993 8:30 PM PDT 1. The Magellan spacecraft started its Transition Experiment this morning at 10:31 AM PDT with an Orbit Trim Maneuver which lowered its periapsis (closest approach to Venus) to 149.4 km. 2. Telemetry indicated that the 11.3 minute burn of the thrusters was normal, and the resulting periapsis altitude was 149.7 km. 3. Following the first atmospheric drag pass, all subsystems were reported to be nominal. Temperatures of the solar panels increased by about 7 to 9 degrees C as a result of atmospheric friction. This is about half the expected value. 4. The attitude control system generated about 2800 thruster pulses as the control shifted from reaction wheel control to thrusters and back during the pass. Much of this activity is caused by the residual momentum from the wheels being transferred to the body of the craft. 5. Power and Telecom were nominal. 6. Nearly identical telemetry measurements were received following the next two drag passes (Orbits 7628, 7629). 7. During the next four days a series of walk-in trim maneuvers will further lower the periapsis until the spacecraft is in the desired corridor. 8. Based on the present navigation and spacecraft data, the next two OTMs (Orbit Trim Maneuvers) will be the "double down" magnitude. The first of the corridor-adjustment OTMs is scheduled for 5:46 AM PDT tomorrow. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | Never laugh at anyone's /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | dreams. |_____|/ |_|/ |_____|/ | ------------------------------ Date: Wed, 26 May 1993 11:54:44 GMT From: Gary Coffman Subject: Moon Base Newsgroups: sci.space In article <24652@mindlink.bc.ca> Nick_Janow@mindlink.bc.ca (Nick Janow) writes: > >I agree that free space is a better environment for industry. However, I >don't think that the leap in technology is the best choice at this time. A >lunar base might be. The scenario you hint at above requires the development >of new technology and techniques in a lot more areas than a Lunar base would. >Extraction and processing of minerals from an asteroid requires completely >different techniques, and will undoubtedly face many unexpected problems. On >the moon, you can use (modified) existing techniques. Exactly. And those modifications wouldn't be simple or cheap, but most importantly *they would have no application to space processing*. Therefore they are a waste of time and money unless they can stand on their own economic merit. No realistic study of lunar resources shows them to be economically viable, now or any time in the projectable future. However, some ET materials studies do show that processing of comets and asteroids may be economically viable with technologies within our projected reach. Going back to the Moon to develop technique is a dead end drain on resources better spent elsewhere. >>+ The technology and facilities developed with a lunar base project would >>+ greatly reduce the cost of developing open-space projects. It would be a >>+ more gradual development; technology in small steps, rather than one risky >>+ leap. >> >> Are we sure of this? None of the material transport systems developed would >> be useful in open space. > >No? The Al-O rockets sound quite useful for moving things around. >Hydrogen/oxygen rockets fueled from asteroids/comets would be better, but I >expect that developing the technology for that would require a lot more time >and funding. I'm talking here about moving the materials around for processing. You know, things like conveyer belts, trucks, draglines, bulldozers, etc. None of the techniques developed in a gravity well have any application in open space. >> Few of the radiation protection or thermal shielding techniques would >> translate. > >They probably would. I can imagine improvements in small pumps and other >things associated with heat transfer. Techniques developed for turning lunar >dust into shielding and structural elements should be useful, if not directly >applicable to orbital structures. The handling of dust in a vacuum is >probably going to be troublesome, gravity or no gravity. In any event it's certainly going to be *different* in gravity than in free fall. So again few techniques would translate from one arena to another. >> Most of the processes would be totally different because of the gravity >> well and differences in ores. > >That's in favour of building a lunar base first. You can apply a number of >known techniques, rather than having to develop _everything_ all at once. A >lunar mine can use draglines, hoppers, etc, with some modification from >off-the-shelf designs. You can make buildings using good old concrete and >steel construction. :) A zero-g mine is going to be a risky project; not >something you want to base the success of _the_ major space development (the >first one is critical). This is looking under the streetlamp for your dropped keys. Unless Lunar processing can stand on it's own as a viable economic activity, there's no reason to develop these modified techniques and any effort directed toward doing so is just a drag on the development of techniques for economic processing of free space materials that do offer economic return. >> Long term recycling in a closed environment, and teleoperation could both >> be developed just as easily in open space as on Luna. > >No, it would probably be much easier to develop with a couple of seconds >round-trip communication lag than with several hours of lag, and much less >reliable communication links (greater precision and more expensive hardware >needed). That depends on where you start your telepresence development. If you do it in LEO, the delays are even less than at Luna. And if you do it in the next room, with suitable delay lines, it's cheaper still. There's nothing about telepresence or closed cycle environment development that *requires* bases on the Moon, or even in orbit. These techniques are best *matured* right here before being put into space. Once they are matured, replacing the artificial delays with real ones should pose no additional problems. If you are saying that very long delay telepresence is infeasible, I won't argue. That's what closed environments are for, to substitute on the spot humans for ineffective remote humans. Again, such environments are best developed close to home at first, say in the next room. Then they can be migrated to LEO or deep space. There's no need for a Lunar base to develop them. Only if you want to learn to operate at 1/6 G is a Lunar base useful. If your ultimate target is zero G, or 1/3 G, your Lunar experience is of limited value. >>+ A mining company would probably choose a lower-grade ore body in a >>+ temperate, developed area rather than a higher-grade one in Antarctica, >>+ where they'd face new problems (redesigning equipment for extreme cold) >>+ and the hassle of time delays (no FedEx overnight delivery). >> >> Oh, and BTW, every major oil company in the world is itching to drill in >> Antarctica. Only a UN treaty is stopping them. > >Sure, the profits are high and the costs of developing the technology is much >lower than that required for mining asteroids. Much of the technology is >already proven (in cold Arctic winters). Besides, are those companies >itching to develop those oil fields now, or are they itching to stake claims >for future exploitation? :-/ As I pointed out, oil companies, and others, are already operating in extreme environments even though lower grade temperate climate ores remain. That answered your objection. Asteroid and comet mining is high risk, but it's also high return due to the expense of launching materials from Earth's surface. The potential market is *in space* not on Earth. There's probably no ET material economically feasible to return to Earth markets, but ET materials compete against materials launched from Earth's surface. That's currently thousands of dollars a pound for even the most mundane materials. >> The only real scientific mission of value to Luna would be a radio >> observatory on the farside where the sensitive receivers could be shielded >> effectively from the radio noise of Earth. > >Wouldn't it be better to have a large, shielded antenna (or rather, an array >of them) in solar orbit. These could be made of--you guessed it--cheap lunar >aluminum. :) The Lunar farside has one unique advantage over solar orbit for this application, it's always three thousand miles of rock away from Earth's noisemakers. And two weeks a month it's also 3,000 miles of rock away from a noisy fusion reactor. An observatory antipodal to the Earth in it's orbit would be better, assuming it's shielding was sufficient. But it's cheaper for now to do it on the Moon. >> As to interesting targets, I think most industrial space interests would >> rather investigate an Earth crossing comet or asteroid than the Moon. > >Are they doing that today? No? Perhaps they're waiting until there's some >infrastructure first. Inexpensive transfer vehicles and resources might make >the difference for a corporate proposal. Some near-Earth space economic >activity (such as a Lunar base) would provide some markets for such things as >volatiles from asteroids. Large LEO industrial structures would be even better markets, and they'd be cheaper to construct. Large active adsats would want SPS equivalent power levels. This would drive demand for space materials to reduce construction costs. Adsats are excellent examples of high value space manufacturing. Their export, information, is massless and travels at the speed of light. It is worth billions annually to Earthside companies, and it's endlessly renewable. >The mere existence of a major space project reduces the risk of further >projects. I get the impression that it is difficult to get funding/approval >for a project that is totally new and unproven. Private investors might be >more likely to invest in a space manufacturing station if there were people >regularly working in orbit, and there were supplies and services in place for >them to use. I agree, but a Lunar base is "in orbit" only in a pedantic sense. That's why we need stations in orbit, to generate the traffic to make commercial ventures palatable. >> For scientific and public interest, the only other body with evidence of >> open water having moved on it's surface in recent geological time holds the >> highest interest. I'd follow that by tectonically and chemically active >> sites like the moons of the Jovians, and Venus. Mercury is another body of >> considerable interest, one of the coldest, and hottest, spots in the solar >> system, it would give us a location for observing that big fusion reactor >> up close and personal. > >Those are definitely interesting, but they'd be a lot more practical to >investigate if there was some infrastructure in place. How about a nice >long-term plan for space exploration and development? I suggest: > > Lunar resource extraction base (to provide Al & O2, and to develop > vacuum and transfer vehicle technology) > Space stations (to develop zero-g experience/technology, and a > market for space resources) > Near-Earth asteroid exploration/exploitation (to gain access to > more resources, such as carbon and water) > Mars exploration > >I'd sprinkle small scientific missions through there as funding allows. Al-O >boosters and radio/laser receivers on/around Luna could cut the cost of >planetary probes. > >If exploitation of the near-Earth asteroids was successful, and markets for >space resources were developed (ie. some space stations), then the >exploration and exploitation of other asteroids, comets, and planetary bodies >might be carried out by private companies. They're just waiting for someone >else to take the first big risk, and "break the path". :) I agree with this progression except for the Lunar base. It is too costly for the benefit of Lunar oxygen and aluminum to offset. Both can be obtained elsewhere without the necessity of developing a Lunar base. Delta-v requirements to some near Earth asteroids and comets are lower than injection into Lunar orbit and landing. The processing facility can be built in LEO mostly by short lag teleoperations from major components assembled on the ground. This course is cheaper and more direct than adding the unnecessary complication of a Lunar base. >> A lunar base would be a mammoth undertaking. A cometary mining program >> would be similarly large. But the former offers almost no hope of economic >> return while the latter at least has a chance of being profitable. I doubt >> that the deep pockets really want to throw their money away indefinitely by >> betting on the dead horse. One that at least wheezes is a better >> investment. It's akin to attempting to plant a colony in a malarial swamp >> when there is nice fertile high ground just over the next rise. The first >> is just a plant the flag enterprise with continuing massive funding >> required for survival while the second offers a chance at self sufficiency >> and profit. > >No, I see the Lunar resource extraction project as significantly cheaper than >a cometary resource extraction project (don't forget transportation of >resources), and one that provides a useful return, if not a profit. BTW, is >water and hydrocarbons so much more valuable than O2, metals, and silicates? >You need those metals and silicates for the construction of structures to >hold people who will buy your volatiles. :) Metals and silicates are available from asteroids that are energetically less expensive to reach than the lunar surface. Add in the unavailable on the Moon hydrogen and carbon from comets and certain classes of asteroids, and you have an unbeatable combination. There's no material on the Moon that we can't get elsewhere, and without the penalty of fighting that gravity well twice. You've got to start thinking about sailing the sea of space and stop getting sucked down those gravity whirlpools. And that can be taken literally for some transport, solar sails are suitable for cargos that need no special long term protection from the space environment. >Profit is for private companies; government's responsibility is to provide >infrastructure and other support. Even if the Luna project is unprofitable, >the return from the projects that become feasible due to its resources and >existence could provide a good return on the investment. But cutting out the middleman is a time honored custom. By spending government dollars *directly* toward our ultimate objectives, we eliminate the need for commercial interests to depend on *side effects* to boost their competitive position in space. Instead they can compete directly for the government's business by supplying ET materials. The best way to do this is for the government to offer a bounty of $X per pound for materials delivered to a government orbital station. Let the private companies decide how to do it. Pricing should decline on a sliding scale as more materials are purchased to drive competition. These materials could be resold to other private companies at a subsidy at first to encourage orbital industrial development. The government acts as a market maker, but it doesn't get involved in the nuts and bolts of a particular technology, something it doesn't do well anyway. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary 534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | | ------------------------------ Date: Wed, 26 May 1993 12:18:26 GMT From: Gary Coffman Subject: Moon Base Newsgroups: sci.space In article stephens@geod.emr.ca (Dave Stephenson) writes: >gary@ke4zv.uucp (Gary Coffman) writes: > >>The only real scientific mission of value to Luna would be a radio observatory >>on the farside where the sensitive receivers could be shielded effectively >>from the radio noise of Earth. Optical observatories are probably better >>placed in open space because of the microscopic distortions introduced by >>the Lunar gravity field, though there is something to be said for a large >>inactive anchor point. That would be disturbed by lunar mining and blasting, >>so the two are unlikely to coexist happily. > >Wrong about optical observatories. Optical interferometers could be built >on the Moon, as it is a stable structure to optical wavelenght dimensions. >An array of interferometric telescopes on the Moon could image Earth-like >planets around near-by stars. This could not be done on the moving plates >of the Earth, or in space. It's highly unlikely it could be done on Earth, but for the more mundane reason of atmospheric turbulence. In space it could be done by using laser beam interferometers as a reference for the interferometer element spacings. This would allow arbitrarily fine post processing correction depending only on computational power available. Gary -- Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary Destructive Testing Systems | we break it. | uunet!rsiatl!ke4zv!gary 534 Shannon Way | Guaranteed! | emory!kd4nc!ke4zv!gary Lawrenceville, GA 30244 | | ------------------------------ Date: 26 May 1993 11:47:18 -0400 From: Pat Subject: Moon Base Newsgroups: sci.space Careful Gary, you are starting to sound like szabo :-) pat ------------------------------ Date: 26 May 1993 11:58:48 -0400 From: Pat Subject: Tom Wolfe's THE RIGHT STUFF - Truth or Fiction? Newsgroups: sci.space,sci.space.shuttle,rec.arts.books In article <1993May26.033414.24963@ee.ubc.ca> davem@ee.ubc.ca (Dave Michelson) writes: >Regarding your comment about imagining "his first words on making orbit": >If that's a joke, it's too obscure for me. At least in Wolfe's book, Grissom had a reputation for speaking Army Creole. Lines like "F***ing A, Well Told, Bubba" It was a factor in the vote for Sheperd being the first man up. The other astronauts were kind of concerned about Grissoms First words. pat ------------------------------ Date: 26 May 1993 16:02 UT From: Ron Baalke Subject: Voyager Discovers the First Direct Evidence of the Heliopause Newsgroups: sci.space,sci.astro,alt.sci.planetary Paula Cleggett-Haleim Headquarters, Washington, D.C. May 26, 1993 (Phone: 202/358-0883) Mary A. Hardin Jet Propulsion Laboratory, Pasadena, Calif. (Phone: 818/354-5011) RELEASE: 93-099 VOYAGER SPACECRAFT FIND CLUE TO ANOTHER SOLAR SYSTEM MYSTERY Nearly 15 years after they left home, the Voyager 1 and 2 spacecraft have discovered the first direct evidence of the long- sought-after heliopause -- the boundary that separates Earth's solar system from interstellar space. "This discovery is an exciting indication that still more discoveries and surprises lie ahead for the Voyagers as they continue their journey to the outer reaches of our solar system," said Dr. Edward C. Stone, Director of the Jet Propulsion Laboratory (JPL), Pasadena, Calif., and Voyager Project Scientist. Since August 1992, the radio antennas on the spacecraft, called the plasma wave subsystem, have been recording intense low- frequency radio emissions coming from beyond the solar system. For months the source of these radio emissions remained a mystery. "Our interpretation now is that these radio signals are created as a cloud of electrically charged gas, called a plasma, expands from the sun and interacts with the cold interstellar gas beyond the heliopause," said Dr. Don Gurnett, Principal Investigator of the Voyager plasma wave subsystem and a professor at the University of Iowa. The sun is the center of our solar system. The solar wind is a stream of electrically charged particles that flows steadily away from the sun. As the solar wind moves out into space, it creates a magnetized bubble of hot plasma around the sun, called the heliosphere. Eventually, the expanding solar wind encounters the charged particles and magnetic field in the interstellar gas. The boundary created between the solar wind and interstellar gas is the heliopause. "These radio emissions are probably the most powerful radio source in our solar system," said Gurnett. "We've estimated the total power radiated by the signals to be more than 10 trillion watts. However, these radio signals are at such low frequencies, only 2 to 3 kilohertz, that they can't be detected from Earth." In May and June 1992, the sun experienced a period of intense solar activity which emitted a cloud of rapidly moving charged particles. When this cloud of plasma arrived at the heliopause, the particles interacted violently with the interstellar plasma and produced the radio emissions, according to Gurnett. "We've seen the frequency of these radio emissions rise over time. Our assumption that this is the heliopause is based on the fact that there is no other known structure out there that could be causing these signals," Gurnett continued. Because of the Voyagers' unique positions in space, they serendipitously detected and recorded the radio emissions. "Earth-bound scientists would not know this phenomenon was occurring if it weren't for the Voyager spacecraft," Gurnett added. Exactly where the heliopause is remains one of the great unanswered questions in space physics. "It's this Voyager radio data combined with the plasma measurements taken at the spacecraft that give us a better guess about where the heliopause is. Based on the solar wind speed, the time that has elapsed since the mid-1992 solar event and the strength of the radio emissions, my best guess for the upper limit of the heliopause currently is about 90 to 120 astronomical units (AU) from the sun," said Dr. Ralph McNutt, a co-investigator on the Voyager plasma science experiment and a researcher at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. (One AU is equal to 93 million miles (150 million kilometers) or the mean distance from the Earth to the sun.) Voyager 1 currently is at 52 AU (4.9 billion miles or 7.8 billion kilometers from the sun), and Voyager 2 is at 40 AU (3.7 billion miles or 6 billion kilometers) from the sun. Voyager 1 was launched on Sept. 5, 1977 and completed flyby exploration of both Jupiter and Saturn. The spacecraft now is rising above the ecliptic plane -- the plane in which most of the planets orbit the sun -- at an angle of about 35 degrees at a rate of about 320 million miles (about 520 million kilometers) a year. Voyager 2 was launched on Aug. 20, 1977 and also completed visits to Jupiter and Saturn and then went on to explore Uranus and Neptune, completing the reconnaissance of the giant outer planets. The spacecraft is now diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 290 million miles (about 470 million kilometers) a year. Gurnett presented his findings today at a meeting of the American Geophysical Union in Baltimore. The Voyager Interstellar Mission is managed by JPL for NASA's Office of Space Science, Washington, D.C. - end - ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | Never laugh at anyone's /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | dreams. |_____|/ |_|/ |_____|/ | ------------------------------ Date: 26 May 1993 11:42:28 -0400 From: Pat Subject: Why a far side Science station. Newsgroups: sci.space I hate to ask this, but Everytime someone talks about a lunar science base, they say "Far side, Radio dead, no Light glare". Am i missing something, or could some sort of reasonably directional radio antenna or optical scope avoid picking up earth scatter? Sure, you have a big black out zone in the center of the sky where you can't observe, but you'd get a lot of operational advantages from being on the near side, even if you were close to the edges. any comments? pat ------------------------------ Date: Wed, 26 May 1993 13:24:54 GMT From: Alan Carter Subject: Why is everyone picking on Carl Sagan? Newsgroups: sci.space In article <26MAY199308281366@stars.gsfc.nasa.gov>, bhill@stars.gsfc.nasa.gov (Robert S. Hill) writes: |> I think the combination of jealousy and suspicion of popularizers with |> some obvious breaches of taste in Sagan's public self-presentation are |> the reasons some scientists react rather badly to him. (What breaches |> of taste? Nearly all of Cosmos, for example. He did everything but put |> on a cape and pointy hat and wave a magic wand. Ludwig von Drake was a |> more dignified picture of the scientist than Sagan.) I was irritated by the silly spaceship in Cosmos. I kept waiting for a really nifty special effect, but it never happened. That said, I suggest that much of the value of the series was in its ability to communicate ideas to an audience *not* already intimately familiar with the subject matter, which it seemed to do well. People are still talking about the series over 10 years later. There is a problem that any scientist will face when trying to communicate with an audience that does not have its own strong motivation to make the effort to listen carefully to carefully qualified and quantified statements. (Such as many students!) The scientist can either stick his or her nose up in the air, dryly mutter on for the given interval, and then wander off feeling self-rightous at having turned yet another audience totally away from nerdy science, or alternatively he or she can use a little showmanship and buzz up the lecture. On network TV, where many of the audience are there by chance to start with, a scientist needs a *lot* of showmanship, or is better off not bothering and doing more harm than good. On the other hand if it is well done, there is the possibility of bringing the fascination and enjoyment of science to a wider audience, that is expected to pay taxes to fund much of science whether they understand what it's for or not. Would anyone be a scientist if it wasn't for the fun bits? Anyway, the evolution cartoon was brilliant and the image of "A World War II every second for the length of a summer afternoon" most potent, although I laughed at the review in a UK newspaper that talked about the possibility of "Yumens in the Doonz of Murruz" :-) |> Jealousy of |> popularizers is one of those unfortunate things that happens in any |> specialized profession, but Sagan did nothing to disarm it. He goes and gets the funding *and doesn't even apologise*? The swine. |> |> My understanding is that he has had a solid, productive scientific |> career in the usual sense of that term. He did co-author the English |> edition of I. S. Shklovskii's book on exobiology, which is probably |> where the humorous, but evidently incorrect, thesis legend came from. Even worse. Now let's see if he weighs the same as a duck so we can burn him. Alan P.S. Anyone heard the rumour that Sagan did the voice for Kermit the Frog? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 1 Belle Vue Court |"We've entered a synchronous | Home: 0684 564438 32 Belle Vue Terrace | orbit above the southern | Away: 0628 784351 Great Malvern | pole." | Work: 0628 794137 Worcestershire | | WR14 4PZ | Lt. Commander Geordi LaForge | Temporary: agc@bnr.ca England | Star Trek The Next Generation| Permanent: alan@gid.co.uk ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ------------------------------ End of Space Digest Volume 16 : Issue 632 ------------------------------