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News
Without a hitch : News : Oswego Ledger-Sentinel : Hometown Newspaper for Oswego and Montgomery, IllinoisWithout a hitch
| The team of NASA scientists that successfully guided comet capsule landing
| by Nancy Atkinson
| 1/19/2006
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A little spacecraft named Stardust has arrived safe at home, having traveled three billion miles, successfully completed its mission in space, brought back to Earth samples of a comet’s coma and interstellar dust particles.
Two Oswego natives, Neil Mottinger and Christopher Potts, both Oswego High School graduates, were part of the teams working together at NASA’s Jet Propulsion Laboratory in California to accomplish these tasks. Mottinger was part of the Navigation and Entry, Descent and Landing teams, while Potts was the Technical Supervisor of the Flight Path Control group.
Stardust was launched in 1999, and just over two years ago, in January 2004, the spacecraft performed a risky and historic flyby of Comet Wild 2 (pronounced “Vilt 2”) to capture the samples and take pictures of the comet’s nucleus.
The trickiest part of the mission, however, may have been bringing the Stardust sample return capsule back through Earth’s atmosphere and safely landing it in the Utah desert.
The capsule landed in the US Air Force’s Utah Test and Training Range (UTTR), southwest of Salt Lake City, on Sunday at 4:10 a.m. CST, two minutes ahead of schedule.
For the successful re-entry and landing, the Navigation team targeted the capsule’s entry to a specific point in the Earth’s atmosphere to within eight 100ths of a degree. One mission manager compared that feat to hitting the eye of a sewing needle from across the room.
The desk-sized spacecraft’s design has provided unprecedented navigation challenges during its entire seven-year entire mission, culminating with the Earth return.
“Navigating this spacecraft has always been extremely difficult because the attitude control thrusters are all mounted on the same side of the spacecraft,” said Mottinger.
The thrusters provide gentle pushes that allow a spacecraft to maintain the correct position while in flight. Normally, most spacecraft have their thrusters placed equally around all sides, but Stardust’s thrusters were positioned so the plume of the thrusters wouldn’t contaminate the particle collector. “This ‘unbalanced’ thruster design causes a velocity change every time the spacecraft needs to control its attitude, which can occur hundreds of times a day,” Potts explained. “Each thruster pulse is extremely small, but the large number adds up to a significant effect on the trajectory.”
Consequently, the Navigation team needed to closely monitor the daily activity of the spacecraft.
“It’s a little like trying to catch a knuckleball,” said Potts, “As the spacecraft trajectory can change noticeably as it reacts to its local space environment.”
Riding a spaceborne “bucking bronco”
Mottinger said that in some aspects, the spacecraft is almost like a bucking bronco.
“It is impossible to predict when the thrusters will fire during normal spacecraft operations,” he said, “let alone the times when it goes into a safe mode, firing the thrusters quite frequently to obtaining a ‘safe’ attitude, awaiting further instructions from Earth.”
Mottinger added that the Navigation team has been monitoring the spacecraft around the clock since the first of the year.
On Jan. 5, the teams at JPL successfully performed a trajectory correction maneuver (TCM), a planned firing of the thrusters that put the spacecraft on target for re-entry. The final planned TCM occurred on Friday, just 29 hours before re-entry. Mottinger said the maneuver changed the velocity of the spacecraft by about one meter per second, targeting it precisely for touchdown.
Later, the 100 pound capsule entered the Earth’s atmosphere 410,000 feet over the Pacific Ocean. The velocity of the sample return capsule reached 28,860 miles per hour as it traveled over California and Nevada, the fastest of any human-made object on record.
The capsule released a drogue parachute at approximately 105,000 feet, and at 10,000 feet the main parachute deployed. After landing, teams of helicopters recovered the capsule and brought it to a temporary clean room at the UTTR before transferring it to the Johnson Space Center in Houston.
Mottinger said that if the Navigation team had decided that the spacecraft was not in the correct trajectory, or if for some reason the sample return capsule did not release, it was possible to fire the thrusters and bring the entire spacecraft into solar orbit. However, it would take four years for Stardust to line up again correctly to release the capsule.
Particles collected could unlock science secrets
The Stardust scientists believe they have collected thousands of particles of cometary and interstellar dust, many smaller than the width of a human hair. The particles were collected from the coma or “tail,” a cloud of gas and dust that surrounds a comet.
Comets are made of ice and dust, formed from the same materials as the sun and planets. Comets are To determine the makeup of the particles, scientists will cut the samples into even smaller pieces and investigate them with powerful microscopes.
The collector is about the size and shape of a tennis racquet, and is made of a unique substance called Aerogel. Aerogel is made of silicon, but is 99.8 percent air. It feels like an extremely light, very fine, dry sponge, and it has the ability to capture fast moving dust. It’s very strong, and will easily survive the capsule’s landing on solid ground.
Both Mottinger and Potts said that during the past few weeks, the Navigation team has gone through tests, training and several full rehearsals for the spacecraft’s return.
“We spend a large amount of time postulating what could go wrong and making sure there’s an appropriate response to correct the problem,” Potts said.
Potts graduated from Oswego High School in 1980 and is the son of former OHS chemistry and physics instructor Charles Potts. Potts has been at JPL since 1984, working on missions such as Voyager and Galileo. He was the Navigation Deputy Team Chief for the Mars Exploration Rovers.
Potts was inspired to pursue a career in astronomical engineering by Neil Mottinger, who graduated from OHS in 1962, and who was also a student of Potts’ father. Mottinger started working at JPL in 1967, specializing in deep space navigation for several JPL projects and for hundreds of launches sponsored by the entire international space community and tracked by JPL’s Deep Space Network.
Over the years, Mottinger occasionally returned to Oswego to give presentations about his work at JPL in Charles Potts’ science classes. The day Mottinger visited Potts’ class was an “eye-opening experience,” Potts recalled, adding he realized he wanted to follow a career path similar to Mottinger’s.
The two Oswego alums have only had the opportunity to work together on a few JPL missions, so they said they’re happy to have the opportunity to collaborate on Stardust, especially given the project’s importance.
“The entire Navigation team realizes we’re responsible for delivering a ‘priceless’ cargo of pristine cometary material samples from a comet’s coma,” said Potts. “These samples represent a glimpse back in time at the early formation of the solar system. There’s little doubt that new science discoveries will be made which will influence the direction of future space exploration.”
•Nancy Atkinson is a free-lance journalist from Rochester, Ill. |
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