SPACE.com -- Stardust Powers On; More Matter Collected

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	Stardust Powers On; More Matter Collected By Robin Lloyd Science Editor posted: 06:30 pm ET 21 February 2001

Stardust situation

Fresh from a zip past Earth en route to a comet, NASA's stardust spacecraft has already picked up another micro-passenger -- a mote of interstellar dust.

This makes the seventh dust "hit" for the solar-winged probe that's bound for a 2004 encounter with Comet Wild 2. Mission scientists hope Stardust's wings of ultralight aerogel capture a cometary sample there for the probe to return to Earth two years later.

Galileo Update

Engineers are narrowing down possible causes for an intermittent problem with the camera on NASA"s Galileo spacecraft that may be related toeffects of Jupiter"s radiation belts.The spacecraft signaled an alarm from the camera system three times while Galileo passed close to Jupiter from Dec. 28, 2000, to Jan. 1, 2001. Each time, the camera either restored itself to normal functioning or was restored by commands from the ground.

"We are able to clear the fault by power-cycling the instrument -- turning the power off and on -- and reloading its memory. The fact that the camera can fix itself without our intervention is puzzling but provides valuable information to analyze what is happening," said Eilene Theilig, Galileo project manager JPL.

Experiments at JPL with an engineering model of the camera system are aiding analysis of events on the spacecraft. The main suspect is an amplifier in the circuitry that processes signals from the camera"s CCD (charge-coupled device), a light-sensor grid akin to those in video cameras. "The investigation is continuing," Theilig said.

During its first four months of operation last year, Stardust's Comet and Interstellar Dust Analyzer (CIDA) instrument registered six dust hits, said Tom Duxbury, Stardust's project manager at NASA's Jet Propulsion Laboratory (JPL). That instrument was turned off during Stardust's recent pass by Earth to pick up speed, and then turned on again just over a week ago.

"Within the first week, we've had the first dust hit and we have the first data on that on the ground," Duxbury said on Wednesday. "We believe it's from the interstellar dust stream that flows within our galaxy through our solar system."

It will take weeks to fully analyze the latest data, but studies of previous hits revealed a surprise -- the particles had much more mass than expected, suggesting molecular aggregates of a combination of simple elements rather than smaller clumps of just one or two atoms of hydrogen, helium, carbon or iron.

'No concern' with thruster firings

Zooming along at about 12.4 miles (20 kilometers) per second, the desk-sized Stardust currently is en route to Wild 2, a comet that orbits roughly between Mars and Jupiter.

Contrary to some news reports, the spacecraft's propulsion system is operating effectively and should get Stardust to Wild 2 on schedule and with sufficient fuel remaining.

Since Stardust's launch in February 1999, engineers had one primary problem to solve -- gasses escaping from somewhere on the craft were smudging Stardust's camera. Engineers eventually rolled the spacecraft so it got a blast of sunlight to burn away most of the problem.

Low on a list of unexplainable mission outcomes has been a finding that Stardust's thrusters, for the past year, have been firing twice rather than once at times when the probe veers close to 15 degrees off its planned trajectory.

"It's not a problem. It's not a concern," Duxbury said. Engineers hope to capture data from one of those double firings in upcoming weeks so they can match it against situations duplicable by a spacecraft simulator at JPL.

JPL manages the mission. The spacecraft was built by Lockheed Martin Astronautics in Denver.

"There is no possibility of losing communication with the spacecraft," Duxbury said. "There is no concern about navigating past the comet and back to Earth. There is no concern about running out of fuel. We have absolutely no concerns in any of those areas."

What's next

Engineers have been receiving healthy signals from the spacecraft, which engineers resumed collecting via Stardust's "faster" medium-gain antenna after the probe's January 15 Earth flyby. Stardust has three antennas that send and receive data at different rates, each providing a trade-off between cost of operation and effectiveness.

The Discovery-class mission will be considered a reasonable success if it completes the Wild 2 flyby and radios back dust data. It'll be considered a huge success if it returns the comet sample to Earth. In January 2006, a Stardust return capsule is to parachute down to the Utah desert, carrying cometary specimens.

Scientists want to know what comprises comets, once called "dirty iceballs," since they are thought to contain remnants of the early solar system and possible clues to the origin of life and water at Earth.

The real risk

The Wild 2 encounter is looking fairly likely these days but engineers may have their fingers crossed at that time. Stardust is cloaked with three layers of bulletproof material to shield it from cometary material that could be traveling at speeds six times faster than a bullet shot from a gun.

"If there happens to be one big (piece of the comet) laying in wait for us, it could penetrate these shields, it could potentially knock off a solar panel or whatever," Duxbury said. "But based on all our studies, testing and simulations, the probability of such a hit from a large enough particle to give us a problem is basically near zero."