One for the Record Books: The Stardust Sample Return Mission

Artist conception of Stardust encountering Comet Wild 2.

Artist conception of Stardust encountering Comet Wild 2.

This is one of the most interesting, but little known, missions NASA has ever undertaken. Stardust was the first U.S. space mission dedicated solely to returning extraterrestrial material from beyond the Moon. I am pleased to have played a role in acquiring the return capsule for the National Air and Space Museum where is it currently on display.

Stardust was launched on February 7, 1999, on a 3 billion-mile round trip to rendezvous with Comet Wild 2, captured comet and interstellar dust in a unique return capsule, and returned that capsule with cometary samples for analysis by Earth-based scientists. It was the fourth NASA Discovery mission, a series of low-cost missions, following Mars Pathfinder, Earth Asteroid Rendezvous (NEAR), and Lunar Prospector. Seven years later, the journey ended with the capsule streaking across the sky and parachuting to a landing on U.S. soil at the Utah Test and Training Range on January 15, 2006.

The Stardust mission originated at the Jet Propulsion laboratory in response to NASA’s 1994 Discovery Announcement of Opportunity (AO) which invited mission proposals that could be developed under a budget of less than $150 million. While it did not win funding in 1994, Stardust was approved by NASA the next year. While missions with objectives of returning cometary samples had been proposed earlier, it was not until the discovery of extrasolar planets and the existence of thousands—perhaps millions—of small icy bodies in the solar system that the NASA science leadership accepted the necessity of such a comet rendezvous mission.

Stardust as a concept emerged when Dr. Peter Tsou, a scientist at the Jet Propulsion Laboratory (JPL), operated for NASA by JPL, proposed a cometary sample return using an “Aerogel” substance to capture particles of a comet’s tail. The Aerogel used on Stardust was first discovered in 1931 by Steven S. Kistler of the College of the Pacific in Stockton, California. A silica substance of great resilience, Aerogel had small commercial uses and was only available in small quantities before Stardust. Tsou refined and manufactured the Aerogel used on Stardust at JPL, making it more rugged that what was already available for use in the mission. The success of Aerogel on Stardust prompted its transfer for commercial uses in a host of other settings. Especially, it found use as insulation for buildings and other types of structures.

To accomplish Stardust Tsou brought aboard Dr. Donald Brownlee of the University of Washington, who served as the Principal Investigator for the science mission. The two had collaborated for more than twenty years in the study of cosmic dust and comets and this project offered the opportunity for the first time to recover particles from these icy bodies. They persuaded Dr. Benton Clark of Lockheed Martin to join the team as the chief designer of the spacecraft and a sample return capsule needed to accomplish the mission.

Scientists examining the comet samples on the "tennis racket" collected by Stardust.

Scientists examining the comet samples on the “tennis racket” collected by Stardust.

The Stardust team proposed an elegant, simple, and successful project that involved the launch of a spacecraft to encounter a comet in the outer Solar System so that it flew a return trajectory, a return capsule that could deliver cometary particles to Earth, and an analysis that would answer core questions about the nature of the small bodies in the outer solar system, the origins of the solar system, and perhaps point directions for future research on the Kuiper Belt and Oort Cloud. They proposed launching on a trajectory for Stardust to encounter Comet P/Wild 2. Using a “tennis racket” arm containing Aerogel that would be exposed to the comet’s tail they could capture tiny particles for later analysis.

The Stardust spacecraft contained guidance, electrical, propulsion, communication, an array of scientific experiments, and other major systems. Its return capsule consisted of six major components: a heat shield, back shell, sample canister, sample collector grids, parachute system, and avionics. Stardust used its extraordinary silicon-based solid Aerogel, a spongelike structure that is 99 percent empty space and only slightly denser than air, to capture the cometary particles. It was deployed in a grid system at the end of the spacecraft’s arm; the cometary particle grid held 32 Aerogel tiles. The canister containing the samples was sealed in an exterior shell that protected them from the heat of reentry. For the next seven years it proceeded as intended, capturing cometary material and returning to Earth where its return capsule safely landed by parachute on January 15, 2006.

The Stardust sample return mission turned out well. The material Stardust returned include interstellar dust that is believed to consist of ancient pre-solar material that includes remnants from the formation of the Solar System. Analysis of that material has already yielded insight into the evolution of the planets and the origins of the Solar System. Since 2006 the dust samples have gone to laboratories around the world for scientists to study the chemical composition of the comet and its signature of the early Solar System. The results of these investigations have been significant if not revolutionary.

Stardust on display at the National Air and Space Museum.

Stardust on display at the National Air and Space Museum.

Scientists found a new type of organic material in the comet dust, material that was volatile in comparison to what we know of these materials on Earth. These appear to be more “primitive” than those found in meteorites reaching this planet. Many scientists believe these samples contain pre-Solar System interstellar materials. They were also surprised to find that Wild 2 contained a diverse array of chemical compositions, suggesting that there had been considerable mixing of solar nebula. What this means, scientists suggest, is that these cometary particles offer a peak into the origins of the Solar System and perhaps the origins of life.

After the return of the sample from Comet Wild 2 in 2006, the main spacecraft took on another assignment, New Exploration of Tempel 1 (NExT), which led to a rendezvous with comet Tempel 1 in 2011. This allowed scientists to study changes in the comet between the time that the Deep Impact mission encountered Tempel 1 comet on July 4, 2005, and the 2011 encounter. Reaching Tempel 1 on February 14, 2011, the Stardust-NExT mission sent back imagery and data on the comet. With fuel depleted on March 24, 2011, the Stardust spacecraft ceased operations after twelve years of operations. At that time, the spacecraft was approximately 194 million miles from Earth.

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One Response to One for the Record Books: The Stardust Sample Return Mission

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