henry@utzoo.uucp (Henry Spencer) (12/04/89)
[Current news from my spies: Pegasus will fly a dress-rehearsal captive- carry mission Dec 7, including everything but pushing the final button. The latest captive-carry test did turn up some minor problems, which are being fixed.] [The following is the rest of the extensive planetary-missions coverage in the Oct 9 issue, hitting the high spots only.] JPL and JSC say that morale in NASA has improved considerably since Bush's Moon/Mars announcement. "This is the first time since President Kennedy... that a President has told us clearly what he wants." JPL outlines tentative approach to a manned Mars mission: 1996 Mars Observer 2, a followon to Mars Observer 1998 Mars Global Network, two launches landing penetrators at 24 sites 2001 two sample-return missions with small rovers 2003 two missions (for redundancy) each carrying a site-reconnaissance orbiter and a communications orbiter 2005 major rover to potential landing site 2007 another 2009 another 2011 sample-return missions, with small rovers, to 2 best sites 2015 manned launch from space station Safety and scientific interest will determine the best landing site, but the best spot would be an ancient lake bed (potential for fossils) with nearby resources (e.g. near-surface permafrost) useful to the mission. A manned mission is considered much more effective than robot missions. [However, I note that quite a bit of the robotic buildup in the above schedule is only tenuously related to the manned mission. A cynic might suspect the existence of a contingency plan which simply scratches the "2015" entry off the schedule...] All of the above missions except the final manned mission are assembled on the ground and use Titan 4 launches. Technologies being pursued for sample-return missions include aerocapture at Mars, intelligent autonomous landing (the Viking landers were lucky: current estimates put the chances of a successful blind landing as low as 60%), and autonomous rendezvous and docking in Mars orbit. [The above-mentioned cynic might observe that aerocapture, although certainly useful, would probably be unnecessary with on-orbit assembly... which seems like a rather easier technology to develop.] Technologies seen as significant problems for rover designs are autonomous sample retrieval (locating and picking up a rock without help, currently a research topic only), lubricants good to -140C, and power supplies that do not require sunlight (unreliable due to Martian dust storms) or batteries (which have problems with the cold). (The probable solution to the power-supply issue is RTGs.) CRAF's penetrator propulsion system has changed from a solid rocket to a liquid rocket to permit postponing choice of the impact velocity until after a first look at the comet. The penetrator design people would really prefer to know now whether they have to deal with fluffy snow or solid ice, but the current design should get at least 30cm into something as hard as sea ice, enough to get the gamma-ray spectrometer into the surface at least. The CRAF main bus is designed to be capable of carrying two penetrators, although the current budget is for one; everyone would prefer to send two, partly as a hedge against trouble and partly so a successful first impact in a "safe" area could be followed by a shot at a more interesting area. Cassini is planned for launch in April 1996 on a Titan/Centaur. It will use an Earth gravity assist, with encounter 26 months after launch. An encounter with asteroid Maja will occur between launch and Earth encounter, and the possibility of a second asteroid encounter is being studied. Cassini then proceeds to Jupiter, for a gravity assist there in Feb 2000. Saturn arrival would be early in 2002. Cassini's Titan probe would probably take 2-3 hours to descend on its parachute, and there is hope of both data on surface hardness (from the probe's accelerometers) and pictures from the surface (if the probe survives impact). The Cassini orbiter will also do Magellan's trick of using its main communications antenna for radar mapping of Titan's surface. The Deep Space Network is gritting its teeth in preparation for Magellan, which will tie up one DSN antenna almost continuously for eight months with 3 terabits of radar data. Some loss of data is likely if there is an emergency on another spacecraft or a need for maintenance downtime on the DSN, although an extended mission could fill in such gaps. [There is hope for an extended mission anyway, since the eight-month primary mission will not do quite the entire surface.] Magellan is in good general health but does have some problems. One is spurious signals in the star tracker, possibly caused by solar protons or electrostatic discharges. The problems seem to be correlated with solar activity. Pioneer Venus's similar tracker has similar problems. The spurious signals are sufficiently away from expected star positions that Magellan's attitude-control computer rejects them, but they do mess up the attempt to determine Magellan's attitude accurately. This is not a trivial problem, since Magellan has to turn back and forth on each orbit to use the same antenna for mapping and data transmission. Magellan will do a star calibration on each orbit, and can miss *one* calibration without significant problems, but successive missed calibrations could hamper communications and mess up the radar data. JPL is developing software filters for the attitude-control computer to reject well-out-of-bounds signals and pick the best of the remaining ones; it is hoped that this will suffice. Magellan's attitude-control computer is also running too warm, which could shorten its life. The expected temperature was 40C, and it's actually 58C. A small error has been found in the thermal models, but it doesn't account for the whole problem. Nobody knows quite what is going on; possibly the solar reflectors have become degraded, but they have not done this on other missions. Mission plans call for the high-gain antenna to shield the computer bay in future, which should keep things under control. Finally, Magellan's thrusters are too warm, especially when the big ones have the Sun shining up their nozzles. Damage is not expected, but one problem is that some of the hydrazine in the fuel lines might decompose. The resulting gas bubbles might cause erratic early firing, a matter of some concern because the big thrusters are vital to proper attitude control when Magellan fires its solid motor to enter Venus orbit. If studies of the problem suggest that hydrazine decomposition is likely, the thrusters will be "burped" with a short firing beforehand. Venus encounter date is Aug 10. Voyager 2 has been running post-Neptune calibration tests before starting interstellar-cruise phase. The Voyagers will still be tracked every day, but they will be reconfigured for a 160bps data rate (compared to 21600 at Neptune) so that DSN's smaller antennas can be used. The major limit on their lifetime is isotope decay in the RTGs, which will run them out of power around 2017. There is hope that they will reach the heliopause (the edge of the Sun's atmosphere) by then; the distance to the heliopause is very uncertain, but current guesses give each Voyager about an 85% chance if no equipment failures occur. Voyager 1's cameras will be used in February to make a mosaic of the solar system from outside. The star background will be supplied by the wide-angle camera, with narrow-angle images of seven of the planets inserted. Pluto is too dim and Mercury is too close to the Sun (which will not be included). The planet images will show them as bright stars only, but the general colors should be right. JPL's Voyager team will drop to 45-50 people next year, with no further encounters to plan and run. (The peak at Neptune was 230.) West Germany's Kayser-Threde company has booked four microgravity flights on Soviet recoverable spacecraft next year. The agreement includes new provisions for launch-site access. This follows a successful protein crystal growth experiment on Resurs-F in September, run by K-T on behalf of Intospace. Intospace is interested in all four 1990 K-T launch slots, although no commitment has been made yet. Payload definition deadline is about six months before launch. The short lead time is one of the most attractive features of dealing with the Soviets: "the West German government finally allowed us to start negotiations with the Soviets last April, things became serious in May, and we flew in September". The biggest obstacle has been glacially slow approval processes in the West German government, which made it necessary for K-T to invoke the cancellation clause in an earlier deal for a 1989 launch slot. (The payload space was used by France's CNES instead.) K-T also holds reservations on Soviet launches in 1991 and 1992. Arianespace is revising the 1989-90 Ariane launch manifest after an electronics problem caused a one-month slip in launch V34, carrying an Intelsat 6. Other recent changes also contributed to revisions. Intelsat is shifting another Intelsat 6 to a Titan, since it wants to use up its two Titan launch reservations quickly, and will put a later one on Ariane in return. An Inmarsat bird scheduled for late next year may not be ready, and there is a strong possibility that Italsat 1, set for next autumn, may be late. It's unusual for Ariane to be waiting for payloads, rather than vice-versa. -- Mars can wait: we've barely | Henry Spencer at U of Toronto Zoology started exploring the Moon. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
jchapin@Neon.Stanford.EDU (John M. Chapin) (12/04/89)
In article <1989Dec4.001327.4287@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: > >JPL outlines tentative approach to a manned Mars mission: > >1996 Mars Observer 2, a followon to Mars Observer >1998 Mars Global Network, two launches landing penetrators at 24 sites >2001 two sample-return missions with small rovers ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ [futher dates deleted] Lest anyone think this is far away... a six-month design study on needed technologies and possibilities for these rovers will start next month at Stanford. The core lectures (with speakers from Ames, JPL, etc) will probably be available on videotape if anyone is interested. The organizers are advertising heavily in places that undergrad engineers hang out. I take this as an encouraging sign that they are trying to get a new generation interested in working on the space program. ------------------------------------------------------------------ John Chapin | The RSA algorithm with 100-digit primes: Stanford Univ. CS Dept. | My personal method for enforcing jchapin@cs.stanford.edu | the bill of rights ------------------------------------------------------------------
kcarroll@utzoo.uucp (Kieran A. Carroll) (12/05/89)
jchapin@Neon.Stanford.EDU (John M. Chapin) writes: > >2001 two sample-return missions with small rovers > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > Lest anyone think this is far away... a six-month design > study on needed technologies and possibilities for these > rovers will start next month at Stanford. However, John, similar design studies have been carried out ever since the early 1970's. Design studies are a necessary but not sufficient condition for carrying out missions :-). I heard once that in the space business, for every mission to be flown, ten preliminary-design-level studies are carried out. And for every preliminary design, ten conceptual design studies are commissioned. -- Kieran A. Carroll @ U of Toronto Aerospace Institute uunet!attcan!utzoo!kcarroll kcarroll@zoo.toronto.edu