[meteorite-list] STARDUST Successfully Images Asteroid Annefrank During Dress Rehearsal

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:13 2004
Message-ID: <200211050317.TAA02873_at_zagami.jpl.nasa.gov>

http://stardust.jpl.nasa.gov/news/news94.html

STARDUST Successfully Images Asteroid Annefrank During Dress Rehearsal
STARDUST Project
November 4, 2002

Late Friday evening Pacific time on November 2, 2002 at
the Jet Propulsion Laboratory (JPL) in Pasadena, California, and at Lockheed
Martin Space Systems - Astronautics (LMA) near Denver, Colorado, the NASA
STARDUST flight team pulled off a tremendously successful close flyby of the
main belt asteroid Annefrank. This flyby was used as an engineering test of
the ground and spacecraft operations that will be implemented at the primary
scientific target, Comet Wild 2 (pronounced "Vilt" 2) just over one year
from now.

STARDUST is a low-cost Discovery Mission that continues to perform as
expected after more than three and a half years into a planned seven-year
mission to rendezvous with Comet Wild 2 in January 2004. STARDUST will
collect cometary dust samples, flowing from the nucleus just hours before
spacecraft flyby, and return the samples to Earth in a Sample Return Capsule
in January 2006. The close flyby of Annefrank offered a unique opportunity
to thoroughly test all planned operations on the spacecraft and ground
support operations which will be used during the rendezvous with Comet Wild
2.

"We performed a full dress rehearsal with the cometary dust collector
deployed as we flew STARDUST within 3,300 kilometers of Annefrank," said
Professor Donald Brownlee, the project's Principal Investigator from the
University of Washington. "The spacecraft was poised in its flyby attitude
with all the science instruments on. The flyby has exceeded all of our
expectations and provided us with unexpected data about the asteroid," said
Brownlee.

The approach geometry to Annefrank was much more difficult than will be the
case for Comet Wild 2. The spacecraft was pointed over 60 degrees off of the
normal Sun and Earth pointing attitude and was running on its battery
in order to attempt to detect and capture images of Annefrank.

"The spacecraft performed every command perfectly and did everything asked
of it," said Allan Cheuvront, Spacecraft Engineer at Lockheed Martin
Space Systems near Denver. "We are thrilled with how well the entire
operation went. We couldn't have asked for better performance from STARDUST
and the images it captured of the asteroid exceeded everyone's expectations.
The spacecraft's pointing, attitude and flight operations were excellent.
This really adds to our level of confidence about how well the spacecraft
will perform when we reach Wild 2," added Cheuvront. Cheuvront and a team of
engineers at Lockheed Martin's spacecraft control center, known as the
Mission Support Area, control the spacecraft in conjunction with JPL and the
Deep Space Network.

The Navigation Camera was straining to see Annefrank during approach. "This
camera was operating at its limit of performance and seeing very dim stars
down to about 11th visual magnitude", said Ray Newburn, the Lead Scientist
for the camera at JPL.

However, the brightness predicted by Drs. Stephen Synnott and Donald Yeomans
of JPL was dimmer than 11th visual magnitude. "We tried everything we could
think of including taking multiple long exposures and adding these on the
ground", said Dr. T. S. Mike Wang, Optical Navigation Specialist at JPL,
"but Annefrank was not cooperating. It was just too dim."

Because of the high probability of not seeing Annefrank during the approach,
the flyby was designed to be successful without having to see it up to 20
minutes from encounter. "A flyby distance of 3,000 km (1,864 miles) was
chosen so that there was no risk of the spacecraft flying near any possible
dust environment or small satellites of Annefrank", said Ed Hirst, JPL
Mission Design Manager. "We also wanted to ensure that Annefrank would be in
the camera view at the start of the encounter sequence," added Hirst.

Since Annefrank was not seen in the approach images, the flight team felt
that the asteroid was at least as dim as predicted and possibly even dimmer.
The team decided to send up a new encounter configuration file and set the
initial flyby exposures longer. "We had a planned uplink six hours before
encounter for this very purpose," said Robert Ryan, Mission Manager at JPL.
"We had some communications problems the day before that gave us some
difficulty, but NASA's Deep Space Network gave us highest priority, and
excellent communications on Friday, allowing us to play back earlier images
we missed as well as sending our final encounter commands," added Ryan.

At 8:00 pm (PST) Friday evening, communications were established with the
spacecraft to watch its pre-loaded sequence command turn the spacecraft away
from the Sun and Earth into its flyby attitude. "We have built up over three
years of flight experience and a tremendous amount of confidence and respect
for our spacecraft to perform such operations routinely," said Joe Vellinga,
STARDUST Program Manager at Lockheed Martin who led the development and
manufacture of the spacecraft. "The spacecraft did not miss a beat during
its flyby and it maintained all critical thermal, power, attitude, memory
and reserves at or above design levels," added Vellinga.

The main function to be tested during flyby was a sophisticated flight
computer program that would take over control of the spacecraft to keep the
camera view locked on Annefrank during a 25-minute period around its closest
encounter. "This software was a derivative of the nucleus tracking software
successfully flown on the Deep Space 1 (DS1) flyby of Borrelly," said Dr.
Shyam Bhaskaran, developer of the algorithms at JPL. "Based upon my previous
experience on DS1, it performed up to my expectations with this encounter at
Annefrank with over 60 successful images having Annefrank right in the
middle of each image," added Bhaskaran. David Gingerich, Flight Software
specialist at LMA who implemented and tested the nucleus tracking software
said, "its performance was executed just like the coach drew it on the
blackboard."

Over 70 encounter images were obtained that show a typical small solar
system body, highly irregularly shaped and cratered. Annefrank is about
twice as large as predicted, at least 6 kilometers in diameter, but darker than
expected and therefore more difficult to detect in the early images. Not
only did the camera perform well but the University of Chicago Dust Flux
Measurement Instrument (DFMI) and the German Cometary and Interstellar Dust
Analyzer (CIDA) performed as expected.

Professor Tom Economou, DFMI scientist from University of Chicago, stated
"we ran for 28 minutes as we will at Wild 2 with DFMI performing all
expected functions". Dr. Jochen Kissel, Lead Scientist for CIDA from Max
Planck Institute in Garching, Germany, said "I will be able to put CIDA into
an even better configuration at Wild 2 based upon the Annefrank experience."
Both dust instrument teams are combing through their data to see if by
chance they may have seen a dust particle.

"Performing such flight testing before the primary encounter is a critical
part of reducing risks and significantly increasing the probability of
success when we reach Wild 2", said JPL Project Manager, Thomas Duxbury. "We
have performed exhaustive testing and training with LMA at their spacecraft
test laboratory and through flight simulations, but these cannot totally
replace actual flight operations testing. We learned a lot that will improve
our operations at Wild 2 based upon the lessons learned at Annefrank. The
bottom line is that if Annefrank had been Wild 2, we would have succeeded in
every respect," added Duxbury.

"I applaud the entire flight team," said Don Brownlee. "We could not have
asked for more, except possibly for Annefrank to be a little brighter.
However, for everything that we could control with the spacecraft, we were
nearly perfect.

Even though this was an engineering test, the flyby with Annefrank provided
new information previously unknown about the asteroid about its size, shape,
spin state and brightness as a function of viewing angle.

"It was an exciting Friday evening for those of us involved in this
mission," Brownlee said. "We captured images of a primitive asteroid with a
highly significant name and one whose size turned out to be similar to the
asteroid that likely killed the dinosaurs 65 million years ago. We have now
validated STARDUST's systems and operations and we are eagerly awaiting our
encounter with Comet Wild 2, just over one year from now".

Asteroid Annefrank images are available here:

http://stardust.jpl.nasa.gov/photo/annefrank.html
http://photojournal.jpl.nasa.gov/catalog/PIA02885
http://photojournal.jpl.nasa.gov/catalog/PIA02886

IMAGE CAPTION

Image of Asteroid 5535 Annefrank taken by the Stardust spacecraft just prior
to closest approach. The gray scale figure on the right show a partially
illuminated, highly irregularly shaped asteroid, typical of all small bodies
imaged in our solar system. The STARDUST camera resolution was sufficient to
show that Annefrank was about 8 km in length, twice the predicted size from
Earth-based observations. The surface reflects about 0.1 - 0.2 % of the
sunlight, slightly less than predicted. A few craters many hundreds of meters
are seen as well as surface brightness variations due to changes in solar
illumination as well as albedo variation. These variations are exaggerated in
the false color image to the left. Both images have been digitally enhanced
and resampled.

For more information on the Stardust mission -- the first ever comet
sample return mission -- please visit the Stardust home page:

http://stardust.jpl.nasa.gov
Received on Mon 04 Nov 2002 10:17:41 PM PST