[meteorite-list] Deep Space 1 Defied Odds, Photographs Comet in Risky Flyby

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:49:02 2004
Message-ID: <200109231945.MAA24166_at_zagami.jpl.nasa.gov>


Deep Space 1 Defied Odds, Photographs Comet in Risky Flyby
By Robert Roy Britt
22 September 2001

NASA's Deep Space 1 spacecraft defied deadly odds late
Saturday, dodging potentially mission-ending comet dust
while sucking down its final drops of fuel in making a
successful flyby of comet Borrelly.

The craft snapped black-and-white photos of the comet's
nucleus from inside the coma, a halo of dust grains and
atomic material burned off the comet by the Sun. It is only the
third time a spacecraft passed close enough to capture
images of a comet's nucleus.

Donald Yeomans, a comet expert at NASA's Jet Propulsion
Laboratory, said he and his colleagues had gotten a sneak
peak of about 30 images Saturday evening and that full
resolution versions would be downloaded from the spacecraft
to Earth overnight and into Sunday.

"These are really remarkable," Yeomans said in a telephone
interview Saturday night. "As expected, there were lots of

Yeomans couldn't say what those surprises were, however,
because NASA is holding the images and will release them at
a press conference in coming days. But he said they would
be very important and useful for the study of comets. [What
researchers hope to learn.]

Some 30 ecstatic mission managers at JPL watched the
images download from a craft that had succeeded in doing
something it wasn't designed to do, and pulling it off after a
long and battering trip that is near its end.

"There was sustained applause," Yeomans said.

Deep Space 1 passed approximately 1,250 miles (2,000
kilometers) from the comet while traveling at 36,900 mph
(16.5 kilometers per second).

Twin Russian spacecraft, Vega 1 and Vega 2, imaged comet
Halley in March 1986. The snapshots helped direct a Halley
flyby later that same month by the European Space Agency's
Giotto mission, which buzzed its target at just 373 miles (600
km) away.

But Deep Space 1 was not designed for a comet flyby, and
NASA had worried that dust might pummel the unprotected
craft. It was a game of odds, and the probe appears to have
sneaked between the widespread particles unharmed.

"There was no evidence of a dust hit," Yeomans said.

The encounter took place at about 6:30 p.m. ET, roughly 125
million miles (200 million kilometers) from the Sun, between
the orbits of Earth and Mars. Signals confirming the
successful encounter were received on Earth at 6:43 p.m. ET,
and data containing the first clues to the composition of the
comet came a few hours after the close brush.

Researchers know very little about the composition of
comets. But they are considered to be pristine
representatives of the material that was present when the
solar system formed.

The press conference may be scheduled for Tuesday, but that
was not immediately clear. [SPACE.com will provide
continuing coverage as this story unfolds and the images are

During the flyby of comet Borrelly, Deep Space 1 had also
been instructed to take other measures of the icy rock. The
probe was asked to produce infrared images that would help
researchers explore the comet's surface. And sensors that
monitor the ion propulsion were reprogrammed to listen for
magnetic fields and plasma waves in and around the comet.

This data all appeared to be gathered and would be
downloaded through the weekend, Yeomans said.

Other researchers have planned ground-based observations of
comet Borrelly, as well as studies using the Hubble Space
Telescope. They hope to combine all the data, along with
what Deep Space 1 has gathered, to paint a detailed picture
of the comet.

"The images and other data we collected from comet Borrelly
so far will help scientists learn a great deal about these
intriguing members of the solar system family," said Marc
Rayman, project manager of Deep Space 1.

Several hours before the encounter, the spacecraft began
using various instruments to observe the comet, JPL officials
said. The observations became more extensive about an
hour-and-a-half before the closest approach, when for two
minutes the probe's infrared spectrometer collected data that
will help scientists understand the overall composition of the
surface of the comet's nucleus.

Deep Space 1 took its first black-and-white image of the
comet 32 minutes before the closest pass, and the best
picture of comet Borrelly was taken just a few minutes before
closest approach, according to plan, mission managers said.

Two minutes before closest approach, ion and electron
monitors that were originally designed to monitor the craft's
engine were used instead to examine dust and gas near the

The flyby is one more feather in the cap for Deep Space 1,
which launched in 1998 and was designed to test a dozen
futuristic technologies, including its high-tech ion engine.
Science was never a primary goal of the mission.

Rayman had said before the flyby that besides the dust, he
was concerned that the craft might run out of the fuel it uses
to make small adjustments to its attitude and trajectory. And
because of a previous failure to its star-tracking instrument,
Deep Space 1 had to use the same camera that obtained the
comet images as a navigation device.

The craft has also been twice battered by solar storms. And it
is thought to be very low on hydrazine, a fuel it uses to fire
thrusters that adjust its attitude and direction.

Rayman, part of a team of about dozen people who now
monitor the craft during an extended mission period, said
before the encounter that it's as though Deep Space 1 "is
kept flying with duct tape and good wishes."

So how did it feel Saturday night?

"It was just tremendously exciting to see this aged and
wounded bird pull off this remarkably complex and risky
assignment so well," an exhausted Rayman said. "I honestly
did not think it was up to that task."

If the probe continues in good health, engineers will run its ion
engine through a series of tests that were considered too
risky before. The tests may cause the ion engine to fail. By
late November, if the craft is still operating, NASA will cease
communications with it.
Received on Sun 23 Sep 2001 03:45:06 PM PDT

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