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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!
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