Tom Duxbury
STARDUST Flight Director
The aerogel collector was successfully deployed today 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 collect
on 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.
For more information on the STARDUST mission – the first ever
comet sample return mission – please visit the STARDUST home page:
