Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Sat, 19 May 90 02:38:20 -0400 (EDT) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sat, 19 May 90 02:37:52 -0400 (EDT) Subject: SPACE Digest V11 #428 SPACE Digest Volume 11 : Issue 428 Today's Topics: Galileo Update - 05/18/90 Re: Sagan vs. asteroids ---------------------------------------------------------------------- Date: 18 May 90 21:37:01 GMT From: swrinde!zaphod.mps.ohio-state.edu!sdd.hp.com!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov!baalke@ucsd.edu (Ron Baalke) Subject: Galileo Update - 05/18/90 GALILEO MISSION STATUS REPORT May 18, 1990 As of noon Friday (PDT) , May 18, 1990, the Galileo spacecraft is 97,221,520 miles from the Earth, 33,004,890 miles from Venus traveling at a heliocentric velocity of 63,880 miles per hour. The spacecraft continues in cruise mode-dual spin with a spin rate of 3.15 rmp. Round trip light time is 17 minutes, 22 seconds. The spacecraft successfully performed both portions of the Trajectory Course Manuever (TCM-4B) on May 11 and May 12. Preliminary assessments indicate that the spacecraft system performance was very good throughout the two day, 10 segment maneuver. Operation was, in general, near predicted levels for all spacecraft subsystems. Articulation and Attitude Control Subsystem (AACS) and Retropropulsion (RPM) performance was without incident and the largest pointing error observed was about 12 mrad, after the fourth segment on May 12. This error was significantly smaller than the nearly 23 mrad observed during TCM-4A in April 90. After a sequence planned correction, the pointing error was reduced to less than 1 mrad. As a consequence of the pointing errors seen in TCM-4A, changes were made to the TCM-4B maneuver design to reduce pointing error excursions and include pointing corrections after the second, fourth and fifth burn segments to correct for accumulated error. The RPM thruster and cluster temperatures were near predicted values. The L1B thruster temperature reached a peak temperature of about 170 degree C, higher than that observed in TCM-4A. The higher temperature was expected and due to thruster increased on-time planned during TCM-4B. The cluster temperature reached about 49 degree C compared with a predicted upper limit of about 70 degree C. RPM tank pressures and temperatures observed were near predicted levels. Preliminary analysis indicates the regulators opened near predicted levels at tank pressures of about 17.1 bars. The AC and DC bus imbalance measurements fluctuated only slightly (1 to 4 DN) during the first maneuver portion on May 11 but the DC imbalance measurement exhibited a significant excursion (25 DN) during the second maneuver portion on May 12; the AC imbalance measurement changed only 1 DN. Subsequent to the burn the DC measurement returned close to its initial pre-burn value. The AC/DC imbalance measurements remained fairly stable, except as noted during TCM-4B on May 12. Subsequent to the TCM, the DC measurement fluctuated about 1 volt (10 DN) while the AC measurement fluctuated about 0.8 volt (4 DN). All other power-related measurements (bus voltage, bus currents and shunt currents) and other subsystem measurements all were as expected. Preliminary radio tracking navigation data indicates that the TCM-4B maneuver imparted near the required delta velocity (11.3 m/sec) with some small underburn. Investigation is in process to understand the reasons for the observed underburn. Further collection and analysis of radio navigation data is currently in process. Commands were sent on May 12 to reconfigure the Extreme Ultraviolet (EUV) instrument in an attempt to capture unique scientific observations including atomic oxygen in the coma of the Comet Austin. Subsequent to the instrument reconfiguration, EUV data indicated that the anticipated comet data was not collected even though the commands were properly transmitted and received. Consequently, additional commands were sent on May 15 to perform EUV memory readout (MRO) activities to aid in investigative analysis. Preliminary analysis indicates the EUV responded properly; further analysis is in process. It is pointed out that earlier EUV comet data via MRO was successfully returned and definite confirmation of atomic oxygen was made. A SITURN to lead the sun was successfully performed on May 15. This SITURN, about 9 degrees, was the largest turn performed to date; spacecraft performance for this activity was as expected and without incident. This large turn resulted in the spacecraft leading the sun by about 6 degrees. Larger sun-lead angles are possible now since the spacecraft is beyond 1 AU from the sun and the sun gate fault monitors are disabled. Cruise Science Memory Readouts (MROs) were successfully performed for the EUV, Magnetometer (MAG) and Dust Detector (DDS) instruments on May 15 and May 18. The Energetic Particles Detector (EPD) instrument was powered on and commanded from Sector O back to Sector 4 on May 15, subsequent to the TCM-4B maneuver. As part of the general EPD activity, an EPD MRO was performed. After the MRO, the EPD was turned off. An attitude control spin detector sensor calibration was successfully performed on May 16. The spin detector signal is used by the attitude control system as the source of spin rate data when the spacecraft is near sun point with gyros unpowered and when star scanner spin rate data is unusable. Spacecraft performance for this calibration activity was as expected and without incident. The twelfth RPM thruster "flushing" activity was successfully performed on May 18. The activity flushed the Z, L, and S thrusters only. The P thrusters were not flushed since they are used periodically to perform SITURNS. These activities were performed to 40 bps and consequently thruster temperature profiles were not available due to low telemetry sample rate. Successful flushing was inferred from other spacecraft measurements/events including attitude control performance and thruster counts. _ _____ _ | | | __ \ | | Ron Baalke | baalke@mars.jpl.nasa.gov | | | |__) | | | Jet Propulsion Lab | baalke@jems.jpl.nasa.gov ___| | | ___/ | |___ M/S 301-355 | |_____| |_| |_____| Pasadena, CA 91109 | ------------------------------ Date: 18 May 90 20:43:11 GMT From: mnetor!utzoo!henry@uunet.uu.net (Henry Spencer) Subject: Re: Sagan vs. asteroids In article <15505@bfmny0.UU.NET> tneff@bfmny0.UU.NET (Tom Neff) writes: >>The point is, when LBJ talked about space, everyone *knew* this was a >>politician speaking. But people still think of Sagan as a scientist, >>and incorrectly attribute primarily scientific motives to his statements. > >Bull. The man in the street only knows about him because of the TV >shows. He's a telegenic public figure who speaks his mind, and does so >fairly well. And is thought of as an honest scientist, not as one of those scheming, conniving politicians with dubious ulterior motives. How would you react if the same words came out of Gary Hart's mouth? >I have listened to him defend the international Mars mission on TV, and >he does so in a very straightforward way: he says Mars is the next great >challenge for human exploration, and that doing it in cooperation with >the Soviets is a great challenge for world peace. No hidden motives >there! And no pseudoscientific trappings. To be polite about it, there is violent disagreement about whether Mars is the next great challenge for human exploration, and much of the support for that notion is the result of Sagan's propagandizing for it. The hidden motive is that the "world peace" part of it is the priority, and the scientific value is irrelevant. (One could get much more scientific return much more cheaply, or get a much better sustained spaceflight program at similar cost, by ignoring the international cooperation and planning a broader and more systematic program.) -- Life is too short to spend | Henry Spencer at U of Toronto Zoology debugging Intel parts. -Van J.| uunet!attcan!utzoo!henry henry@zoo.toronto.edu ------------------------------ End of SPACE Digest V11 #428 *******************