by Tom Duxbury
Stardust Flight Director
Washington - February 23, 2000 - The aerogel collector has been successfully deployed to begin the interstellar dust collection. The commanded timeline was followed precisely with the heat shield on the Sample Return Capsule (SRC) opening, followed by the shoulder motor moving the collector out of the SRC and then finally the wrist motor extending the collector fully to its collection position where it sticks above the spacecraft shielding and into the cometary dust stream.
The deployment was confirmed during deployment with small torques detected by the attitude control system for the proper duration as well as the motors turning for the proper time duration. The final confirmation came with the shoulder and wrist microswitches being triggered when deployment was complete.
In the spacecraft current orbit where it just came out of solar conjuction, its inertial velocity direction is about 50 degrees away from traveling directly with the interstellar dust stream. Over the next few months as the spacecraft orbit curves around the sun, the spacecraft motion will parallel the dust stream motion.
After the collector was fully deployed today and all subsystems were verified to be operating nominally, a command was sent to move the collector 50 degrees in the direction of closing to position the collector surface area normal to the interstellar dust stream flow.
Every few weeks we will command this angle by a few degrees to keep the collector surface normal to the stream. Near the end of this first interstellar collection period, the collector will be fully deployed again. The collection will continue until at least 25 May 2000; however we are currently exploring extending this period by a few additional weeks.
There are no microswitches in between the full open and full close positions to tell us the exact position of the aerogel collector. We will control this position during the next few months by commanding the wrist motor for a fixed length of time to provide the desired angle movement and verify this movement from telemetered wrist motor operating data. To reach its current 50 deg offset angle, the wrist motor was power on for about 20 seconds which was executed perfectly.
The collector has two sides of aerogel: side A for interstellar dust collection and side B for cometary dust collection. We control which side of the collector is exposed to by orienting the spacecraft in inertial space.
Currently the spacecraft is oriented with its dust shields pointing in the direction of its motion about the sun and the interstellar dust particles hitting the back side (side A) of the collector. The spacecraft orientation with be reversed relative to the comet Wild 2 particle stream so that the dust shields will protect the spacecraft while the collector is extended above these shields into the oncoming dust stream.
As its name indicates, the interstellar particles to be collected now are from outside of our solar system. There is a very tenuous dust cloud within our galaxy, the Milky Way, which our solar system is moving through. The direction of the interstellar dust is opposite to the motion of the sun, which drags the planets with it, relative to the particle media. Thus the dust motion is small relative to the solar system motion that is controlling the direction of interstellar dust passing through our solar system.
The interstellar dust stream was detected many years ago by earth orbiting spacecraft and information on this stream has been improved by early Pioneer and Voyager spacecraft.
More recently the Ulysses and Galileo spacecraft have confirmed the stream direction as well as indicated that the density of particles in the stream is very low.
With the size of the STARDUST collector being only about 0.1 meter square, we expect to collecton the order of 100 such particles during the 2 collection periods. We have just started the historic first collection period and will perform the second collection period in about two years, when again the spacecraft is traveling in the direction of the particle stream.
High praise goes to the spacecraft builder and flight operations team at Lockheed Martin Astronautics in Denver, Colorado for this successful deployment and the start of this historic sample collection. The sample will be returned to earth for detailed science analyses in 2006 after the SRC lands in the Utah Test and Training Range.
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