Stardust status report
Posted: Feb. 26, 2000
The spacecraft transitioned back to Gyro Based Attitude Mode with the Inertial Measurement Unit (IMU) powered on to provide high rate attitude data during the aerogel grid deployment. Also six images were taken with the Star Camera. These images will be analyzed to determine the health of the Star Camera and provide information concerning why the number of valid stars occasionally drops from 10 to 4 stars.
A historic milestone in planetary exploration was achieved by STARDUST this week. The aerogel collector was successfully deployed to begin its 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 dust shielding and into the interstellar dust stream.
The deployment was confirmed during deployment with small torques detected by the attitude control system 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's current orbit where it just came out of solar conjuction, its inertial velocity direction is about 49 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 and all subsystems were verified to be operating normally, a command was sent to move the collector 49 degrees in the direction of closing to position the collector surface area normal to the interstellar dust stream flow. Every few weeks the wrist motor will be commanded to change 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. This historic collection will continue until 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 shoulder and wrist positions to tell us the exact position of the aerogel collector. Control and knowledge of this position during the next few months is achieved by commanding the wrist motor for a fixed length of time to provide the desired angle movement and then verify this movement from telemetered wrist motor operating data. To reach its current 49 deg offset angle, the wrist motor was power on for about 20 seconds, which was executed perfectly.
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 earlier Pioneer and Voyager spacecraft have improved information on this stream. 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.=20 With the size of the STARDUST collector being only about 0.1 meter square, on the order of 100 such particles are expected to be collected during the 2 collection periods. The second collection period is 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 the sample collection. The interstellar particles will be returned to earth with the Wild 2 particles for detailed science analyses in 2006 after the SRC lands in the Utah Test and Training Range.
Following the successful deployment, three images were taken with the Navigation Camera. These images were taken through the Optical Navigation filter (widest bandwidth) with the calibration lamp on. Two images had an exposure time of 200 milliseconds and the third had an exposure duration of 1 second. These images will be analyzed to help determine the cause of the apparent decrease in Navigation Camera sensitivity observed when the last star images were taken in October.
Also, after the aerogel collector deployment, the spacecraft transitioned back to All Stellar attitude mode.
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