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Planetary News: Stardust (2006)Stardust: Comet Mission Returns Home Sunday with Sample OnboardBy A.J.S. Rayl
Faster than a speeding bullet -- actually, more than 10 times faster than a speeding bullet, Stardust will conclude its 7-year, 4.63 billion kilometer (2.88 billion mile) round-trip journey to comet Wild 2 Sunday, January 15, Pacific Standard Time (PST), making an historic re-entry in the wee morning hours to drop its precious comet cargo in the Utah desert well before dawn. “We will light up the sky,” Tom Duxbury, Stardust project manager, told journalists at a pre-landing press briefing held yesterday at Dugway Proving Ground in Utah. Traveling at 12.8 kilometers or 8 miles per second – fast enough to go from San Francisco to Los Angeles in one minute, Stardust’s re-entry will set a new standard as the fastest returning spacecraft, surpassing the record set in May 1969 during the return of the Apollo X command module. It is set to break through Earth’s atmosphere just before 2 a.m. Pacific Standard Time (PST) / 3 a.m. Mountain Standard Time (MST) / 10 Greenwich Mean Time (GMT) over the Pacific Ocean. “It will move over the west coast of northern California and will light the sky from California through central Oregon and on through Nevada and Idaho and into Utah,” Duxbury elaborated.
The sample return capsule – which weighs 45.7 kilograms (101 pounds) and resembles a mini Apollo capsule -- is to land approximately 15 minutes after re-entering, at about 2:12 a.m. PST / 3:12 a.m. MST/ 10:12 GMT on the United States Air Force’s Utah Test and Training Range, located southwest of Salt Lake City. People below the general flightpath should be able to witness Stardust’s return in the pre-dawn sky, Duxbury added. To them, the Stardust capsule will appear as a point of light, passing like a meteor over those northwestern states to its landing at the test range. [The best opportunities for viewing the re-entry will be along Highway 80 between Carlin, Nevada and Elko, Nevada and further east to the Utah border, where the capsule's front side can be observed before it passes over observers on the ground.] “We are nearing the end of quite a fantastic voyage – our spacecraft has traveled further than anything from Earth ever has – and come back,” Stardust Principal Investigator Don Brownlee of the University of Washington, Seattle, reflected yesterday. “We went half-way to Jupiter to meet the comet and collect samples from it. But the comet actually came in from the outer edge of the solar system, out beyond the orbit of Neptune, out by Pluto,” he added. Wild 2 (pronounced Vilt two) is believed to hail from the Kuiper belt, a band of cosmic debris that orbits the Sun beyond Neptune and Pluto. The first project to launch a sample return mission since the Apollo days, Stardust is a $170-million-dollar NASA Discovery mission that in its 7-year-journey actually went around the Sun three times, “and back in time to 4.5 billion years in time to gather these primitive samples that just were released from a comet’s nucleus,” Duxbury summarized. Stardust will perform its final trajectory correction maneuver at 8:53 p.m. tonight PST, which will put it on the specific flightpath to enter the Earth’s atmosphere. And if all goes as planned, by Sunday morning, scientists will have in their hands the world's first preserved samples of the fundamental building blocks of our solar system that formed 4.6 billion years ago. Since locked within these particles are unique chemical and physical data that may hold the record of the formation of the planets and the materials from which they were made, scientists believe in-depth terrestrial analysis of the cometary samples will reveal a lot about comets, as well as the earliest history of the solar system, and perhaps even something about us.
Stardust launched on February 7, 1999, and collected its first interstellar dust from February 2000 through May 2000. On January 15, 2001, Stardust swung back around Earth for a gravity assist to get out to comet Wild 2, and on April 18, 2002, reached aphelion, setting a new distance record. Beginning in August 2002 and through December that year, the mission gathered its second collection of interstellar dust and on November 2, 2002 did a flyby of asteroid AnneFrank. Then on January 2, 2004, Stardust began its landmark encounter with comet Wild 2 flying through the coma, within 147 miles (236 kilometers) of the comet’s nucleus. The spacecraft was pummeled by an estimated one million dust particles and small rocks up to nearly two-tenths of an inch (one-half centimeter) across, but managed to not only survive but take the first images of the inside of a comet and collect particles from inside that nucleus. Those images caught the scientists by surprise. “We were just stunned,” recalled Brownlee. “The comet itself has fantastic features – deep depressions, flat mesas, overhanging walls, and spires, pits, and craters. But the other really exciting thing about what we saw was the material being ejected in its jets . . . the very same particles that the comet was born from . . . so we’re using the comet as a library that picked up records of the creation of our solar system and has been storing them far from the Sun at very low temperatures for 4.5 billion years.”
Despite the “fantastic images,” Brownlee noted that “the main focus” is in the samples. Stardust collected its dust samples by extending one or both of its collection grids as it passed through the target areas. Each collection grid looks something like an oversized handball racket-shaped ice cube tray and is made up of more than 130 aerogel ‘tiles’ -- a strong, thick, lightweight, silica glass that is 99.8 percent air and looks like frozen smoke. While Stardust collected comet stuff on one side of both collection grids, it collected the interstellar dust streaming in from other parts of the galaxy on the reverse sides of the two grids at two other points during the flight. "It's a little bit like collecting BBs by shooting them into Styrofoam," as Scott Sandford, an astrophysicist at NASA Ames and a Stardust mission co-investigator, has described it. “We think a significant fraction of comets will be stardust particles actually older than Earth and older than the Sun, and for drama the stars, and the way you identify those is by their isotopic ratios,” Brownlee said. “There are fabulous tools now to analyze these and a very anxious group of scientists waiting for these samples.” The work, however, will be as tedious as it is exacting. Most of the samples – which total about a thimble full -- will be “smaller than a human hair,” said Brownlee. “Each particle is actually made up of collections of hundreds of thousands of much, much smaller particles, and so one of these particles is really like a rock.” As it currently stands, all systems are ‘go’ for Stardust to release its sample return capsule (SRC) tomorrow, January 14, at 9:57 PST/10:57 MST/ 5:57 a.m. January 15 GMT. About 15 minutes after the release, the spacecraft is to perform a divert burn that will place it in a solar orbit. Along for that ride will be a microchip that contains the names of all Planetary Society members from around the world at the time of Stardust’s launch, the first such collection of names from the public to have made a round trip to space and back. Four hours later, the Stardust return capsule will enter the Earth’s atmosphere and over the Pacific Ocean and continue on a ballistic trajectory to its landing site in Utah. At 32 kilometers (105,000 feet), the first parachute will deploy to further slow the Stardust capsule, and at about 3 kilometers (10,000 feet, the second parachute is to open, bringing the capsule into a final 6.5 minute descent, falling at a leisurely 10 miles-per-hour, approximately the same as a person coming down from skydiving. Three helicopters will be at the ready just outside the 44-x-76 kilometer (27-x-47-mile) landing area to recover the capsule promptly. “If weather permits, we will be going out to retrieve the capsule by helicopter,” confirmed Mike McGee, recovery operations manager, of Lockheed-Martin Space Systems, Denver. “If a storm comes in, we’ve got ground transportation to get us out there . . . in any case, we will retrieve it,” he said. Once the recovery team locates and secures the Stardust capsule, it will double-bag it in the field and fly the entire capsule to a clean room at the Dugway Proving Ground for removal of the sample canister and initial analysis. “If everything goes well, which is what we’re expecting at this time, we should be done about 7 a.m. in the morning [local or Mountain time],” said McGee.
The samples will then be packaged and sent on to a special laboratory at the Johnson Space Center (JSC) south of Houston, Texas, where the samples will be further analyzed, verified, and sectioned. A small portion of the samples will be used to make a preliminary study of the returned material, with the rest to be made available to scientists around the world for research. Although scientists around the world will study this cosmic dust for years to come, a separate team of researchers aboard a NASA DC-8 will be gathering data on the brief re-entry of the Stardust capsule into Earth's atmosphere, confronting the daunting challenge of tracking and observing the conical object as it hurtles through the atmosphere and slows before the spacecraft finally parachutes down in a Utah desert. The goal is to assess how well the capsule's heat shield protects its precious cargo of comet dust and interstellar grains. The return capsule is designed to shoot down through the air at the highest spacecraft re-entry speed into Earth's atmosphere ever, generating extremely high temperatures. A special carbon-based heat shield – which was developed at NASA Ames Research Center to protect the priceless cargo of comet dust and interstellar grains -- is a candidate for potential inclusion on NASA's next planned spaceship, the Crew Exploration Vehicle (CEV), according to agency engineers. This prospective future use is one reason they plan to intently study the capsule as it slams into Earth's atmosphere, and the shield rapidly heats due to friction with the air. One of the goals of the researchers aboard the DC-8 is to measure the capsule's re-entry brightness. Scientists expect it to peak at approximately the brilliance of Venus for roughly 90 seconds. The capsule will be brightest 60 kilometers (37 miles) high over the town of Carlin, Nevada as the spacecraft approaches. This will occur in the early morning cold and darkness on Sunday, January 15, 2006, shortly before the spacecraft parachutes to a landing. At the same time as the DC-8 crew is flying its mission, amateur astronomers, willing to endure the cold of the bitter winter, may contribute to the study by simply photographing the incoming capsule, noting their global positions and later providing that information to mission scientists. Although Stardust’s sister mission – Genesis – crash landed in September 2004 because of a misplaced gravity switch that caused its parachute to fail, this team is confident their ship, despite the fact that it shares much of the same hardware and design elements as its predecessor, will not meet the same fate, and the Stardust team fielded the questions about Stardust’s ability to deliver its goods head on at the press conference. “ “We’ve looked at this in detail -- we know exactly what happened with Genesis – one sensor was in backwards and so the parachute did not deploy,” Duxbury said yesterday. “But even though Genesis impacted hard, a lot of samples were intact and are currently at JSC with the Genesis team.” Once Stardust ejects the return capsule tomorrow night, there is, however, no turning back. The SRC will spin toward the Earth on a ballistic trajectory until it breaks through the Earth’s atmosphere. “There’s no guarantee for [a safe soft landing],” Duxbury admitted. “Space exploration is kind of a tough business.” In the event Stardust does land hard, however, little will be lost, Duxbury assured. “Mike McGee and his team have practiced for those scenarios. We have a smaller and more rugged return capsule than Genesis, and our collector grid is very thick, hard aluminum, and the aerogel is a very robust material that we have tested it, at more than a few hundred Gs, and it survived just fine,” he said. “So even with a hard landing, we believe we will recover most of, if not all of, our science. Again, the finish line is at JSC, not, and that is where we will get the fruits of all our labor.” That said, Duxbury did allow for the “negligible” possibility that an unforeseen problem could cause them to abort the release of the capsule. “If we decide not to release the SRC, the spacecraft will be diverted and we go around in a 1.5 year orbit around the Sun – and 3 years later, when the spacecraft and Earth are back together, we could do the landing at that time,” he said. In other words., Stardust would go into “a deferred orbit of 3 years” if it was not released as scheduled. Still, no one, he added, is expecting anything but a smooth, soft landing. “The spacecraft has performed perfectly during the 7-year flight,” Duxbury said, “and the team has done a great job.” Stardust@HomeOnce the team has the Stardust samples, they must search the grids for the comet and interstellar dust particles before they can analyze them. They expect to have some results within the first few days and weeks. All told, the scientists hope to find maybe a thimble-full of the interstellar dust, so the task may sound simple enough. But the grains are so few and so tiny that they are completely lost within the cracked and imperfect surface of the aerogel collector that has spent 7 years in space. In fact, they are so embedded that the scientists are asking for the public's help via an Internet-based project called Stardust@home, inspired by the long-running SETI@home. Unlike SETI@home where one’s computer processed all the data, however, Stardust@home will be a hands-on activity. Scientists at the Space Sciences Laboratory at the University of California at Berkeley (UCB) will create "movies" of each tiny section of the aerogel collectors -- 1.6 million movies in all. Each of these movies will be sent electronically to volunteers around the world, who will inspect them for the telltale signs of interstellar dust particles. Because no one knows exactly what these dust tracks will look like, the human eye – and good old-fashioned human intelligence – will be better at spotting them than a computer program. Therefore, each volunteer scanner will need to pass a test by spotting tracks made in test samples. The team will also keep scanners vigilant by occasionally throwing into the mix a “ringer” – an artificially made track – to see if it is found. As an official collaborator in the project, The Planetary Society has put out an all-call to recruit users. To be part of be part of Stardust@home, you will need an easily downloadable "virtual microscope" and some basic online training, and a desire to really do the research, according to Bruce Betts, the Society’s director of projects. The public can begin signing up with Stardust@home in mid-March. Lockheed Martin Space Systems in Denver developed and operates Stardust while JPL, a division of the California Institute of Technology, manages the Stardust mission for NASA's Science Mission Directorate in Washington D.C. NASA's Johnson Space Center contributed to Stardust payload development, and the Johnson Space Center will curate the sample and support analysis and sample allocation. |
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