Date: Sun, 13 Dec 92 05:00:10 From: Space Digest maintainer Reply-To: Space-request@isu.isunet.edu Subject: Space Digest V15 #539 To: Space Digest Readers Precedence: bulk Space Digest Sun, 13 Dec 92 Volume 15 : Issue 539 Today's Topics: Cassini Undergoes Intensive Design Review DC vs Shuttle capabilities Mariner 2's 30th Anniversary Mariner 2 Radio Tracking - 12/28/92 Mariner 2 Venus Flyby - 12/14/62 (2 msgs) New Moon race (was Re: NASA town meetings) Titan what the little bird told Henry 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: 12 Dec 92 00:34:16 GMT From: Ron Baalke Subject: Cassini Undergoes Intensive Design Review Newsgroups: sci.space In article <1992Dec10.232527.643937@locus.com>, hayim@locus.com (Hayim Hendeles) writes... >In article <1992Dec10.053616.8145@news.arc.nasa.gov> baalke@kelvin.jpl.nasa.gov writes: >> ... >> After flybys of Venus (twice), Earth and Jupiter as it loops >>around the sun to pick up energy, Cassini will arrive at Saturn >>in November 2004, beginning a four-year orbital tour of the >>ringed planet and its 18 moons. The Huygens probe will descend to >>the surface of Titan in June 2005. > >Pardon my asking an ignorant question, but I can't understand why it >should take 7 years to get to Saturn. When Voyager went to Jupiter and >Saturn, it took (if I recall correctly) 4 years and a Jupiter flyby to >make it to Saturn. Here, you are using 4 flybys, and it's taking you 7 >years! I would think that if you were to adjust the launch date so that >Jupiter and Saturn were in the same relative positions as they were in >1977 (when Voyager was launched), you could do the same trick again (in >the same 4 years). Inherently, orbiters will take longer to get to their destination than flybyers. Spacecraft that will orbit a planet (like Cassini) tend to be bigger than spacecraft that are on flyby missions because they have to carry additional propellant that will be used for orbit insertion. Cassini is also carrying a Titan probe which adds additional mass to the spacecraft. The orbital mechanics are more constrained for an orbiting mission because the approach speed to the planet has to be less, where this was not much of a concern with Voyager. To further complicate the situation, the U.S. do not have any launch vehicles that are powerful enough to send Cassini on a direct trajectory to the outer planets. To make up for this, the spacecraft has to circle around the inner solar system for gravity assists from Venus and Earth to pick up enough momentum to reach Jupiter, and then slingshot to Saturn. These additional gravity assists add years to the mission. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | The 3 things that children /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | find the most fascinating: |_____|/ |_|/ |_____|/ | space, dinosaurs and ghosts. ------------------------------ Date: 12 Dec 92 18:44:09 GMT From: Greg Moore Subject: DC vs Shuttle capabilities Newsgroups: sci.space In article <1992Dec11.141858.16948@iti.org> aws@iti.org (Allen W. Sherzer) writes: >In article strider@clotho.acm.rpi.edu (Greg Moore) writes: > >> 1) Won't teh crew compartment take up part of the cargo bay? > >Of course. On the other hand the standard interface which makes you do >this reduces integration time which keeps flight rate up and costs down. > You missed my point. If your crew compartment is in the cargo bay, where do you put the satellite? >In the longer run, you may be right. Plumeting launch costs will cause >payload prices to fall since there will be more and cheaper launches >plus the opportunity for on site repair. > I eliminated some stuff above, but wanted to add some stuff here. Actually, plummeting launch costs may contribute to lower payload costs since people will be willing to build a less fault tolerant system knowing that if it fails, they can launch another cheaply. As for on-site repair, for now DC-? fails for the same reason that the Shuttle normally does, it can't get up to GEO, you need a OTV... in which case it doesn't matter in the long run how you get into orbit, as long as it is cheap enough. >> Also, as for retrieval, the Shuttle has shown that it ain't >>easy to do. Will a two day on-orbit time be enough? > >It may take modifications to the DC. At the very least you need to add >a robot arm and an airlock. > Granted, but that's not what I meant. Will you have enough time to rendevous and capture the satelite? It took what 3 days for the shuttle to capture Intelsat VI? That's aday more than DC-?. Also, what type of fuel margin would DC-1 have for IN-orbit manevours? (I realize it has enough for landing, and of course you don't wnt to cut into that for safety reasons.) >> Let's not try to have DC-1 do everything... remember that is >>where the shuttle went wrong. > >But let's use it for what we can. The way to bring costs down fast with >this concept is to use it. > Use it yes, but use it for what it can be used for economically. Let's see, we've added an airlock, an arm, additional on-orbit capacity. Hmm, that adds up, and add complexity. Yes, let's ok at possibilities, but not claim t they are definites. >My view is that we use the basic DC as a 'bus' which can be modified in >small ways to meet diverse missions. Costs are cut because the same assembly >lines are used to make DC1-EOT (Earth orbit transfer), DC1-OMV, and DC1-LM. > I have a question about this. EOT and LM should require roughly the same amount of fuel, no? (as I recall, the energy to get into lunar orbit is about the same as GEO? I'm ignoring landing here). But how economical is it to transport that fuel TO orbit? Am I correct in remembering you saying about 10 DC-1 flights? Also, does it make sense for the DC1-EOT and OMV and LM the same. The requirements for landing gear are different. The requirements for fuel transfer MAY be different. What about thermal protection. LM won't require any to land on the moon, but what about reentering earth orbit or earth landing? >This makes the basid DC a building block of a more extensive space >infrastructure. > Granted. And that is attractive. > Allen > >-- >+---------------------------------------------------------------------------+ >| Allen W. Sherzer | "A great man is one who does nothing but leaves | >| aws@iti.org | nothing undone" | >+----------------------134 DAYS TO FIRST FLIGHT OF DCX----------------------+ ------------------------------ Date: 12 Dec 92 01:03:41 GMT From: Ron Baalke Subject: Mariner 2's 30th Anniversary Newsgroups: sci.space,sci.astro,alt.sci.planetary PUBLIC INFORMATION OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011 Contact: James H. Wilson FOR IMMEDIATE RELEASE December 9, 1992 Thirty years ago, Dec. 14, 1962, the first successful interplanetary traveler reached Venus after a 108-day journey from Earth. Named Mariner 2, it was a 200-kilogram (450-pound) machine carrying six scientific instruments, a two-way radio, a solar power system and assorted electronic and mechanical devices. Its crew, numbering roughly 75, stayed behind at NASA's Jet Propulsion Laboratory. The Mariner planetary spacecraft series began in 1960 as a group of mission studies at JPL; by 1975 there had been 10 Mariner flights, seven of them successful explorations of the inner Solar System. Mariner 2 became the model for planetary space flights, one that emphasized good and copious scientific data collection, utilizing remote sensing of planets and in-situ measurement of the space environment; all of is this supported by high-quality engineering. The resulting program eventually led to close observation of all the planets but Pluto, planetary orbiters and landers, international cooperative missions and flights right out of the Solar System. What became the Mariner 2 mission was authorized by NASA in August 1961, less than a year before the first launch window. The limited capacity of Atlas/Agena, the largest available launch vehicle, severely restricted launch opportunities and spacecraft size. The first launch, Mariner 1, was aborted when its launch vehicle strayed from the safe flight corridor and was destroyed by the Range Safety Officer. Mariner 2 was successful, however; since that trailblazer mission, there have been about four dozen U.S., Soviet and other flights -- the majority successful -- reaching every planet from Mercury to Neptune, plus comets and an asteroid, and one joint U.S.-European mission (still underway) to the poles of the Sun. These are in addition to dozens of lunar spacecraft and the manned lunar flights of Project Apollo. Liftoff A few minutes before 2 a.m. on Aug. 27, 1962, Mariner 2 lifted off the pad at Cape Canaveral aboard its Atlas-Agena rocket. It was nearly as much an experiment for the rocket and spacecraft engineers as for the space scientists intent on observing interplanetary space and the planet Venus. During its three-and-a-half-month odyssey of some 290 million kilometers (180 million miles), reaching a third of the way around the Sun to Venus, Mariner 2 transmitted coded signals continuously to the Earth, mixing scientific measurements of interplanetary dust, magnetism, cosmic rays and solar plasma with engineering data on the health and performance of the spacecraft. As Earth turned beneath the feeble radio transmissions, three great steerable antennas (now the Deep Space Network) captured Mariner's signals in turn, first in California, then Australia, Africa and California again. Mariner 2 suffered and survived a number of unanticipated events during the flight. It lost its attitude orientation; one of the solar panels failed; many temperature readings rose ominously as Mariner approached Venus; and, just before the Venus encounter, the computer/sequencer became erratic. But Mariner automatically recovered its orientation, survived solar heating, and, as sunlight grew more intense, one solar panel did the work of two. When the flight engineers saw the sequencer faltering, they started the encounter sequence by radio commands from Earth. On Dec. 14, 1962, Mariner's infrared and microwave radiometers scanned back and forth across the planet, capturing data that would prove Venus's surface to be fire-hot -- about 425 degrees Celsius or 800 Fahrenheit -- warmed in part by a runaway greenhouse effect in the thick carbon dioxide atmosphere. About three weeks after its historic Venus flyby, Mariner 2 went off the air. Its signal was last received on Jan. 3, 1963. The ability of Mariner's crew and equipment to overcome in- flight problems, and simply to complete the flight to the planet Venus, constituted major technical advances in addition to the scientists' discoveries about Venus and the Solar System. The spacecraft design proved robust, and the attitude-stabilized spacecraft concept feasible for long-term exploration. To Mars Two years later -- Nov. 28, 1964 -- a second-generation Mariner set forth -- this time on an eight-month journey to Mars. Mariner 4, like its predecessor, survived the loss of a twin and the rigors of an alien environment. Also like the earlier Mariner it was extremely light in weight, solar-powered, fully stabilized, automated, in constant contact with a team of engineers and scientists back on Earth and bristling with instruments. Unlike Mariner 2, this machine could see: a TV camera and tape recorder caught the first close-up pictures of the surface of Mars, revealing moon-like craters, some of them topped with frost. The navigators sent Mariner 4 behind Mars, letting the radio link with Earth serve as a probe of the atmospheric density and revealing a surface pressure less than 1 percent of Earth's. Following the pattern set by Mariner 2 and Mariner 4, NASA/JPL sent spacecraft back to Venus and Mars, into Mars orbit and to Mercury. The latter flight, made by Mariner 10 in 1973- 74, used the gravitational field of Venus to boost it inward to the orbit of Mercury. In the 1970s, various USSR spacecraft orbited Venus, entered its thick atmosphere, even landed. In 1976, two NASA scientific stations landed on Mars, remaining in operation for several years. This Viking mission, encompassing two large Mars-orbiting spacecraft as well as the two landers, conducted a comprehensive, long-term mapping survey of the entire planet, spot investigations of special areas (including the moons Phobos and Deimos), and atmospheric studies. Viking also produced biological, chemical, meteorological, physical and image data collected at the landing sites. A Grand Tour A year later two spacecraft were launched on what became the grand tour of the outer planets: the Voyager mission to Jupiter, Saturn, Uranus, Neptune and -- still going -- beyond the Solar System to interstellar space. Voyager 1 used Jupiter's gravitational field to speed it on to Saturn and then, after tens of thousands of images of the two planets and their many satellites, it left the plane of the ecliptic. Voyager 2 also flew past Jupiter (1979) and Saturn (1981), but its path was designed to use additional gravity assists to sling it onward to Uranus (1986) and Neptune (1989). The two Voyagers took a total of well over 100,000 images of the outer planets, rings and satellites, as well as millions of chemical spectra, magnetic and radiation measurements. They discovered rings around Jupiter, volcanoes on Io, shepherding satellites in Saturn's rings, new moons around Uranus and Neptune, geysers on Triton. The last imaging sequence was Voyager 1's portrait of the Solar System, showing Earth and six other planets as sparks in a dark sky lit by a single bright star, the Sun. Two spin-stabilized Pioneer spacecraft had preceded the Voyagers to Jupiter, and one of them went on to Saturn, before heading out of the System. Thus, four NASA spacecraft are now actively searching, in different directions, for the frontier between solar and interstellar space; at least one is expected to detect it in the next quarter-century. New Era Shortly before Voyager 2's Neptune encounter, a new generation of planetary exploration began. Magellan set out for Venus in 1989 to map the surface from orbit using imaging radar. A Pioneer spinning spacecraft had been orbiting Venus for more than a decade, completing a low-resolution radar topographic map and many other planetary and solar studies; the Soviets compiled radar images of the northern part of Venus, landed more cameras and deployed balloons into the atmosphere. Magellan mapped 99 percent of the surface at high resolution, parts of it in stereo, and is presently mapping the gravitational field. In October 1989, NASA/JPL's Galileo spacecraft began a gravity-assisted journey to Jupiter, where it will place a probe in the atmosphere and observe planet and satellites from orbit for two years. On the way, Galileo performed gravity-assist encounters with Venus and the Earth and made the first close flyby of asteroid Gaspra in 1991. In a joint mission with the European Space Agency, NASA launched the Ulysses spacecraft in 1990 on a flight over the poles of the Sun. To achieve high orbital inclination, the spacecraft did a gravity-assist flyby of Jupiter, measuring the magnetosphere as it did so. In September 1992, Mars Observer was launched to Mars. It is scheduled to go into orbit around the planet in August 1993 and make many observations during a period of one Martian year. As 1992 rounded out three decades of scientific growth and achievement in observing and understanding the Solar System and the development of highly sophisticated spacecraft and missions, NASA began to look anew to the small, purposeful, higher-risk kind of mission represented by Mariner 2 thirty years ago. ##### ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | The 3 things that children /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | find the most fascinating: |_____|/ |_|/ |_____|/ | space, dinosaurs and ghosts. ------------------------------ Date: 12 Dec 92 01:47:15 GMT From: Ron Baalke Subject: Mariner 2 Radio Tracking - 12/28/92 Newsgroups: sci.space,sci.astro,alt.sci.planetary OFFICE OF PUBLIC EDUCATION AND INFORMATION CALIFORNIA INSTITUTE OF TECHNOLOGY JET PROPULSION LABORATORY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIFORNIA. FOR RELEASE: P.M.'s of Friday, December 28, 1962 RADIO TRACKING OF MARINER II AND ITS SCIENTIFIC IMPLICATIONS Mariner II's fly-by of Venus on December 14 has produced the most accurate estimate yet of the mass of our sister planet, two scientists from the California Institute of Technology Jet Propulsion Laboratory reported today. This information was re- vealed at a meeting of the American Geophysical Union at Stanford University, in a paper by John D. Anderson and George Null, describing their preliminary analysis of the trajectory data obtained during the 109-day flight of Mariner II from earth to Venus. According to Anderson, who presented the paper, they find the mass of Venus a value of 0.81485 times the mass of the earth, with a probable error of 0.015 percent. They said that their analysis is continuing, using additional data obtained before and after the encounter with Venus, and that their final result will probably alter the quoted value slightly and still further reduce the probable error. For comparison, the mass of the earth is known to be approximately 13,173,000,000,000,000,000,000,000 pounds (about 13 septillion pounds). The only method known to astronomers for determining the mass of other planets is through the observation of their gravitational effects on other bodies in the solar system. Thus, for planets having satellites (moons), the determination can be made with considerable accuracy. In the case of Venus, which has no known satellites, no natural object has ever been observed to pass close to it, and hence all estimates of its mass made before 1940 were both inaccurate and erroneous. Two more recent determinations are in agreement with the new Mariner value, but have much less precision. In 1943, G. M. Clemence published a value equivalent to 0.813 times the earth's mass, with a probable error of 0.34 percent, based upon his study of the astronomical records of the observations of the motions of the planet Mercury through the year 1767 to 1937. In 1954, E. W. Rabe obtained a value equivalent to 0.8148, with a probable error of 0.05 percent, from records of the motion of the minor planet, Eros, over two decades. In contrast, the data required to deduce the new more accurate mass of Venus were obtained by the Jet Propulsion Laboratory's Goldstone Tracking Station during two 10-hour observations of Mariner, on the day of its passage of Venus and the previous day. The data obtained was a so-called "two-way Doppler" measurement, involving a round trip by a radio signal. A signal at a frequency of approximately 960 megacycles per second was sent from Goldstone and was received by Mariner, 3 minutes 12.5 seconds later. The spacecraft then shifted the frequency of the signal slightly and sent it back to Goldstone, where it was compared to the original signal. From this comparison the spacecraft velocity relative to the earth, approximately 40,000 miles per hour, can be calculated within about 0.01 miles per hour, and it was the change in this velocity amounting to approximately 3,000 miles per hour, produced by the gravitational field of Venus which gave the scientists the necessary data to determine the mass of the planet. Anderson also said that further analysis of the data will probably refine our knowledge of another particularly important astronomical constant, the Astronomical Unit--the mean distance between the sun and the earth. At present, the measurement of this unit by a variety of conventional astronomical techniques are slightly in disagree- ment with those obtained by bouncing radar beams off of Venus, as has recently been done again by the Goldstone station. The two- way Doppler measurement is an independent measurement, and may help to resolve the inconsistency. 224-12/62 ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | The 3 things that children /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | find the most fascinating: |_____|/ |_|/ |_____|/ | space, dinosaurs and ghosts. ------------------------------ Date: 12 Dec 92 01:35:15 GMT From: Ron Baalke Subject: Mariner 2 Venus Flyby - 12/14/62 Newsgroups: sci.space,sci.astro,alt.sci.planetary In honor of the 30th anniversary of Mariner 2's flyby of Venus, I am posting three of the Mariner 2 press releases from 1962. Ron Baalke OFFICE OF PUBLIC EDUCATION AND INFORMATION CALIFORNIA INSTITUTE OF TECHNOLOGY JET PROPULSION LABORATORY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIFORNIA FOR RELEASE: To A.M.'s of Friday, December 14, 1962 MARINER II VENUS ENCOUNTER Man's first chance to obtain information from another planet will come on December 14 when the Mariner II spacecraft passes approximately 21,000 miles from Venus. Mariner's radiometers will pierce the cloud cover to determine surface temperature and temperatures in the atmosphere. Instruments will determine the strength of the magnetic field and nature of the radiation belts. The entire spacecraft will measure the strength of the gravitational field as it speeds and slows on its curving path near Venus. The 447-pound spacecraft was launched by the National Aeronautics and Space Administration on August 27, 1962, at 1:53 a.m. from the Atlantic Missile Range, Cape Canaveral, Florida. It was built, and is now being tracked, by the California Institute of Technology Jet Propulsion Laboratory. The launch vehicle was the Atlas-Agena B. When the Mariner arrives at Venus it will have traveled 182,000,000 miles during its 109-day journey through space. During its long cruise, that extended almost halfway around the Sun, the spacecraft set a long distance communication record of 36,000,000 miles, and performed the first successful guidance maneuver in space. The Mariner II carries six scientific experiments. Four of these, turned on by ground command two days after launch, are: a magnetometer, an ion chamber and particle flux detector, a solar plasma detector, and a cosmic dust counter. They have been making invaluable measurements during Mariner's curving trip towards Venus and when the spacecraft arrives will measure magnetic fields, radiations and dust particles around the planet. Two other experiments--a microwave radiometer and an infrared radiometer--will scan the surface and the atmosphere of Venus for 42 minutes as Mariner rushes by. All telemetry information gathered during Mariner's voyage is transmitted by Mariner to a network of ground receiving stations called the Deep Space Instrumentation Facility (DSIF) which are located in Goldstone, California, Woomera, Australia, and Johannesburg, South Africa. Mariner was launched in a way that would cause it to fall inward toward the Sun. This was accomplished by timing the injection so that the spacecraft would leave earth in a direction opposite from that of the Earth in its orbit around the Sun. Since Mariner's speed around the Sun was less than that of the Earth, it could not maintain a circular orbit like Earth and the Sun's gravity caused it to be drawn inward so that it would eventually intercept the trajectory of Venus. By nine days after launch, DSIF tracking data processed at JPL's Space Flight Operations Center in Pasadena, showed that Mariner would arrive at a rendezvous ahead of Venus, missing the planet by 233,000 miles. This launch dispersion was well within the correction capability of the 50-pound-thrust rocket motor aboard the spacecraft. During the midcourse maneuver, the motor was fired for 27 seconds affecting a slight decrease in velocity. This guidance correction will bring Mariner to a point 21,000 miles from the planet. This point is well within the original target area, a pie-shaped region extending between 8000 to 40,000 miles from Venus. Before Mariner passes Venus a sequence of events will begin. The first of these will be the activation of a stored command in the spacecraft's central computing and sequencing system that turns on the radiometer scan device. If for some reason this command is not initiated by the spacecraft, it will be sent by the DSIF Goldstone station. The radiometers, located on the hexagonal deck of the spacecraft, are 20 inches in diameter and five inches deep. They are mounted on a swivel and are driven by an electric motor in a 120 degree scanning motion. During the pass by Venus, the microwave and infrared energy will be collected and transmitted to Earth. Prior to activation of the radiometers, the Mariner was in a "cruise mode." In this mode, it was continuously telemeter- ing the first 20 seconds of information provided by its four interplanetary scientific instruments, and then 16 seconds of engineering data. Engineering data is concerned with the condi- tions aboard the spacecraft and include temperatures, pressures, voltages and angular positions. During the fly-by, the data format changes from "cruise mode" to "encounter mode" and Mariner devotes itself exclusively to gathering and sending scientific data. At the time that the radiometer's scan mechanism is turned on, Mariner will be approaching the planet from the dark side and moving in a downward direction. As seen from Venus, the spacecraft will be moving in a direction to the right and below the Sun. As Mariner cruises past Venus its solar panels will remain locked on the Sun to obtain electrical power, as they did throughout the long mission. The radiometers point in a direction perpendicular to the roll axis of the spacecraft and move in a nodding motion across the surface of Venus at a rate of one-tenth of a degree per minute. As Mariner passes Venus, the radiometers will first scan the dark side and then the sunlit side. This planetary scanning period will last for 42 minutes. During this time, the findings of all sox scientific experiments will be transmitted to the Woomera and Goldstone DSIF stations. At 66 minutes before the point of closest approach, or 10:55 a.m., December 14, Mariner will be 25,262 miles from Venus. At that time its velocity will have increased to approximately 87,000 mph due to the gravitational pull of the planet. At this time the radiometers should detect the planet's surface for the first time. At 44 minutes before the point of closest approach, or 11:17 a.m., Mariner will pass the planet's terminator, or dividing line between light and darkness. It will still be moving downward and picking up speed. Drawn by the gravitational field of Venus the spacecraft continues to accelerate. By 11:37 a.m. the scanning period ends as Venus moves out of sight of the radiometers. At that point in time, Mariner will be going approximately 87,000 mph. Venus will be approximately 21,700 miles away while the Earth is about 36,000,000 miles away. Twenty-three minutes later, at 12:01 p.m., Mariner will reach the position of closest approach, approximately 21,000 miles from Venus. It will be traveling approximately 88,400 mph. The gravitational attraction of Venus will have increased Mariner's velocity by 1400 mph in one hour. As the spacecraft starts moving away from Venus, gravity reverses its effect and starts slowing the spacecraft down. In addition to changing the speed of the spacecraft, the gravitational field also will bend Mariner's trajectory by about 25 degrees during encounter. After closest approach Mariner will be instructed to turn off its radiometers and return to the cruise mode. When the command is obeyed the spacecraft will resume the sending of engineering data and will continue to take measurements with its interplanetary instruments. It will continue in this mode until the mission is completed. On December 27, it will reach its closest point to the Sun, 65,539,000 miles. At this time, its velocity will be approximately 85,300 mph. It will be 2,700,000 miles from Venus and Mariner then will be 44,213,000 miles from Earth in a helio- centric orbit around the Sun. Uncertainties in Mariner's trajectory resulted from: the effect of solar pressure, the mass and gravitational fields of the Earth and Venus, the exact location of ground tracking stations and the astronomical unit. Refinements in these uncertainties will be achieved by analysis of the tracking and doppler data collected during Mariner's trip and during the encounter phase when Mariner's trajectory is perturbed by Venus gravity. The doppler effect is a principle of physics in which the frequency of radio waves appear to increase when a transmitter and receiver are approaching each other, and to decrease when they are moving apart. The speed of Mariner is determined by analysis of the frequency of its signals. 219-12/62 ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@kelvin.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |__ M/S 525-3684 Telos | The 3 things that children /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | find the most fascinating: |_____|/ |_|/ |_____|/ | space, dinosaurs and ghosts. ------------------------------ Date: 11 Dec 92 17:55:50 GMT From: Lord Vader Subject: Mariner 2 Venus Flyby - 12/14/62 Newsgroups: sci.space,sci.astro,alt.sci.planetary In honor of the achievements of the Mariner 2 mission, we should take this time to contemplate the significance of the planned shutdown of the operational Magellan spacecraft scheduled for mid 1993. We have only made a limited number of interplanetary spacecraft and thus it seems almost criminal to shut off a spacecraft that is for the most part fully operational. Keep Magellan Alive. ------------------------------ Date: Sat, 12 Dec 92 12:11:31 -0600 From: pgf@srl03.cacs.usl.edu (Phil G. Fraering) Subject: New Moon race (was Re: NASA town meetings) Newsgroups: talk.politics.space In talk.politics.space you write: >You missed the point, or ignored the question. Unless you think >we have unlimited resources to do everything we'd like to do >(and we don't), we have to prioritize, doing some things now and >some later. If you think returning to the moon is the thing >to do NOW, fine. Present a convincing argument for it. I'd like >to see us return to the moon. But NASA nad the space community >has never done a convincing job of telling me why we should spend >several billion on that instead of on a number of other alternatives. You're missing the point. A 50 million dollar lunar probe won't be the mission that killed DC-X and DC-Y; NASA is likely to try to kill those programs, though, in order to feed another year of designing the space station and flying the space shuttle. Look at the cost figures for : 1) Doing DC-X, DC-Y... 2) Flying the lunar resource probe 3) One year's worth of shuttle operations, 4) The Space Station's budget overruns, which are basically caused by the shuttle's shrinking capabilities... The main obstacle to developing a cheap launcher is the conception that the launcher needs to be expensive, i.e. cost billions upon billions of dollars, to begin with. >The US made a mistake in the 60s. We should have developed a better >space infrastructure (shuttle, station) before going to the moon. >Then going to the moon wouldn't have been such a one-shot thing. >We'd have placed ourselves permanently in space, and not so subject >to every Congressional budget whim. Go over and read sci.space and the ongoing discussion of new launcher technology. Please. I'm cross-posting this to sci.space. I think it needs to be done, since 1) I can't post to talk.politics.space, and 2) So many people _can't_ get talk.pol.space that I'm beginning to think the group creation was just done to stifle dissent. >I do to. I'd like to see us on the moon and Mars and farther before >I die. But that alone is not a good enough reason to justify >doing it now and not in 10 or 20 years. I'd like to see NASA >make a case for going to the moon soon. But if they can't convince >me (and I'm an easy sell, since I want to see this happen) how >are they going to convince the person in the street (who is >paying the bill) that it's a good idea to do now. (Note that I >don't question that, medium and long term, that it is a very good >idea. I've just yet to be convinced that we should take resources >away from the space station and launcer improvements at this >time.) Putting the money towards a lunar program would probably be the only way to _get_ launcher improvements because otherwise it's just going to go to Scuttle operations... >The mission is to make use of near-Earth space. We have a good >consensus in the country now that this is a good idea. NASA >should use this support to improve how well we can get into >near-Earth space, as well as improve the ways human beings can >work in near-Earth space. Then, when this is such an integral >part of our lives that Congress, on a whim, can't pull the plug, >we can start moving outward. There is no real consensus of that sort in this country. Other than materials science and MTPE, leo is only good as a staging area. And some of us see MTPE as killing the space program rather than helping it, and materials science as being much more cheaply done than the way NASA wants to do it. >Then it's up to NASA to make a case for them. Among other things, >I think space station work should justify some of this. I also >think once a station is built, it will justify better ways to >get to it, and bigger launch systems to make it easier to add >bigger expansion sections to it. The station isn't that expandable, and is so expensive that 1) it isn't going to create a launch market and 2) When cheaper launchers come along, it'll be cheaper for people who need a station to build their own small ones from scratch. >I think it's some of both. I also think I'm defining infrastructure >more broadly than you are. I don't think we have a good enough >infra-structure yet. We, maybe, now have the equivalent of paved >roads, but we need the equivalent of interstates, at least into >orbit. Or, to use another analogy, when the Europeans settled >North America, they start in New York and settle California. Bit >by bit, the developed a system of roads, cities, and outposts >that helped them farther and farther along the way. Wagon trains >for California left from Kansas City and St. Louis, not from >New York and Boston. Similarly, I think we have to return to >the moon and beyond in such steps. We need our St. Louis in >space: a good, permanent space station, from which we can take >the next step. These aren't roads. Here's a different analogy, since paving space would be very hard: We have Langley's aerodrome. We need Wright flyers. >Jim Mann >Stratus Computer jmann@vineland.pubs.stratus.com ------------------------------ Date: Sat, 12 Dec 92 11:31:53 EST From: John Roberts Subject: Titan -From: gustav@arp.anu.edu.au (Zdzislaw Meglicki) -Subject: Re: Cassini Undergoes Intensive Design Review -Date: 12 Dec 92 04:28:51 GMT -Organization: Centre for Information Science Research, ANU, Canberra, Australia -Could anyone sum up at this stage what is known about Titan and especially -about the question of a possible ocean there. I vaguely recall that some -time ago radio-ranging of Titan returned somewhat mixed signals in this -matter. Recent radar mapping of Titan indicates that it does *not* have large oceans, though there may be smaller bodies of liquid. I don't remember where I read that - probably either Science News or sci.space. -|> To -|> further complicate the situation, the U.S. do not have any launch vehicles -|> that are powerful enough to send Cassini on a direct trajectory to the -|> outer planets. -Right, can't the US build such a vehicle by then? Clearly, if any serious -space exploration is to continue a powerful vehicle like that will be -needed sooner or later anyway. What happened to the idea of nuclear -propulsion? It's the classic "big science" problem - it doesn't make sense to risk a $4 billion mission on an unproven technology, when you can try it on a ~$100 million spacecraft going somewhere else. (Let's hope they try a small nuclear spacecraft sometime soon - but even if they do, the technology is unlikely to be ready in time for Titan, unless they delay it considerably.) John Roberts roberts@cmr.ncsl.nist.gov ------------------------------ Date: 11 Dec 92 17:56:29 GMT From: "Edward V. Wright" Subject: what the little bird told Henry Newsgroups: sci.space In <1992Dec10.192026.16340@ke4zv.uucp> gary@ke4zv.uucp (Gary Coffman) writes: >They're also heavy as I recall, something you don't need in a SSTO. >I appreciated the summary you gave earlier, Henry. It looks like they >have a better test program planned than what has been outlined here >before. I still think their schedule is extremely optimistic and >success oriented, but we'll see. I'd be curious to know the exact date, sometime in the last 20 years, when "success oriented" became a pejorative phrase. Yeah, the project is success oriented. Just like Project Apollo. The alternative, I guess, is for a project to be "failure oriented." I like success better. ------------------------------ End of Space Digest Volume 15 : Issue 539 ------------------------------