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(meteorobs) [ASTRO] Deep Space 1 Mission Log - February 20, 2000




------- Forwarded Message

From: Ron Baalke <BAALKE@KELVIN.JPL.NASAdot gov>
Date: Wed, 1 Mar 2000 21:04:03 GMT
Subject: [ASTRO] Deep Space 1 Mission Log - February 20, 2000

          Dr. Marc Rayman's Deep Space 1 Mission Log
          http://nmp.jpl.nasadot gov/ds1/mrlog.html
 
          Mission Update:

          Thank you for visiting the Deep Space 1 mission status
          information site, the most respected site in the inner
          solar system and the most envied site in the outer solar
          system for information on this bold and exciting mission.
          This message was logged in at 4:00 pm Pacific Time on
          Sunday, February 20. This log is an edited transcript of a
          telephone recording. If you would like to access the same
          information from any place with a telephone, please call
          1-800-391-6654 and select option 3.

          As Deep Space 1 continues its travels far from Earth, the
          focus of the control team's work is to write new computer
          programs for the stalwart little craft. As faithful readers
          of many species know, after having successfully completed
          its primary mission last year, DS1 accepted a new, bonus
          assignment. This extended mission represents NASA's desire
          to continue to reap as many rewards as possible from the
          investment made in DS1. But in November the spacecraft's
          star tracker ceased operating. During the subsequent two
          months, the DS1 operations team devised a new method of
          controlling the spacecraft so that its main antenna could
          be pointed at Earth even without the sensor that had
          previously been so important. Since then, this innovative
          technique, which (as described in detail in the previous
          log) involves monitoring the strength of DS1's radio signal
          to determine exactly where it is pointed, has been used
          repeatedly to conduct communications with the spacecraft.
          But a new system is under development that will allow DS1
          to point without the aid of mission controllers.

          The star tracker, whose inspirational name derives from its
          function of tracking stars, had been responsible for
          helping the spacecraft determine how it was oriented in
          space. This was not part of the autonomous navigation
          system, one of the advanced technologies DS1 tested during
          its primary mission; rather, it was part of what is called
          the attitude control system. To reduce the attitude control
          system's regular reliance on distant Earth, engineers would
          like to replace the method of observing the radio signal to
          calculate the spacecraft's orientation. Of course, all
          there is to work with is what is already on board; the only
          new "equipment" that can be provided is computer programs.
          So engineers are writing new software that will allow the
          computer to control the pointing using images from the
          camera, another one of the 12 technologies that was
          included so that its innovative design could be tested in
          space. This new method builds on the autonomous navigation
          system's capability to analyze the camera's pictures.

          The star tracker worked by photographing the stars wherever
          it was pointed and analyzing the pictures to find familiar
          patterns. This is similar to how you might orient yourself
          at night if you knew the constellations. But the star
          tracker and the camera have very different designs,
          including how large a section of the sky they see at one
          time and how fast they can take a picture and transfer the
          electronic image to the computer. Nevertheless, DS1
          engineers are making good progress on a very clever new
          system that should allow the spacecraft to operate without
          frequent assistance from Earth. In effect, engineers are
          building a new attitude control system on DS1 from across
          the solar system. A tremendous number of complex technical
          details has to be worked out, but the small team that has
          accomplished so much is working hard to restore our deep
          space emissary's capabilities.

          The new software will be radioed to the spacecraft in May;
          then, following a few weeks of tests, DS1 will return to
          thrusting with its ion propulsion system to propel it to an
          encounter with a comet next year. When DS1 was launched,
          controllers had in mind that if the mission were successful
          and if the spacecraft remained healthy, NASA might extend
          its flight to conduct an encounter with Comet Borrelly in
          September 2001. The mission went so surprisingly well that
          they were able to plan for it to visit two comets instead
          of one. But now that the star tracker has stopped, the
          spacecraft has fallen behind in its schedule of thrusting,
          so there is not enough time to do the thrusting necessary
          to keep both appointments. The DS1 science team met last
          month and concluded that the originally planned target
          should be kept. By the way, the science team is happily
          analyzing the infrared observations of Mars made by DS1 in
          November and returned in January once the new method of
          pointing the main antenna at Earth was developed. The
          observations are believed to be the best of their kind ever
          collected.

          Although the primary mission concluded last year, one of
          the most important events of the mission took place this
          month. Over 100 engineers and scientists from NASA as well
          as other government agencies, private industry, and
          academia gathered to discuss the results of the testing of
          DS1's payload of 12 technologies. As the hundreds of
          trillions of devoted readers know, DS1's mission was to
          test these important, high-risk technologies in order to
          reduce the cost and risk of future science missions; DS1
          took the risks so that future missions would not have to.
          That means that in addition to exercising the technologies,
          the results had to be disseminated to potential users. So a
          symposium was conducted in which detailed engineering
          information on all aspects of the technologies was
          presented. These new capabilities may be considered to be
          tools in the tool boxes of designers, and now some
          important and exciting space missions that previously were
          unaffordable or impossible have become feasible.

          Deep Space 1 is now over 1.7 times as far from Earth as the
          Sun is and nearly 670 times as far as the moon. At this
          distance of more than 256 million kilometers, or 159
          million miles, radio signals, traveling at the universal
          limit of the speed of light, take 28 and a half minutes to
          make the round trip.

          Thanks again for logging in!

------- End of Forwarded Message


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