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July 1, 1999
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NASA taps UH astronomer David Tholen for asteroid mission
David Tholen, an astronomer at the University of Hawai'i Institute for Astronomy, is one of a half-dozen U.S. scientists selected by the National Aeronautics and Space Administration (NASA) for the world's first expedition to place a robotic lander on an asteroid and return pieces of the space rock to Earth for in-depth study. The U.S. scientists selected will collaborate with Japanese colleagues on the MUSES-C project, the world's first asteroid sample return mission.
"MUSES-C" stands for Mu Space Engineering Spacecraft, with the "C" signifying it is the third in a series. The mission is a cooperative venture of Japan's Institute of Space and Astronautical Science (ISAS) and NASA.
Asteroid Nereus, a one kilometer-diameter (about one-half mile) object, is the preferred target of the mission. (An alternative target is the asteroid 1989 ML.) "Nereus is one of Earth's closest neighbors, easily accessible for a spacecraft rendezvous and an object of key scientific interest," according to Donald K. Yeomans, NASA's MUSES-C mission project scientist.
David Tholen is an internationally recognized authority on the categorization of asteroids. He will use data from the spacecraft camera to determine the asteroid's rotational state, to estimate the age of the asteroid and its shape and size, as well as other properties such as density.
Nereus is thought to be a relatively unaltered asteroid, having changed little since Earth and the other planets of the inner solar system formed some 4.6 billion years ago. Detailed studies of Nereus and other asteroids are expected to provide scientists with crucial information about Earth's initial chemical composition and the conditions under which it and the other inner planets originally formed.
The MUSES-C spacecraft, provided by the Japanese, will be launched on a Japanese M-5 launch vehicle in January 2002 from Kagoshima Space Center, Japan, toward a touchdown on the asteroid Nereus in April 2003. The Japanese spacecraft will deliver a NASA-provided miniature robotic rover to the surface of Nereus to study the asteroid up close. The MUSES-C spacecraft will gather samples of the asteroid and depart for Earth, leaving the rover behind. The asteroid samples will be returned to Earth in January 2006.
Nereus has a gravity field estimated to be about 100,000 times weaker than Earth's. This presents an unusual challenge for engineers at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, where the miniaturized rover is being developed. The cigar box-size rover is being designed to take advantage of the low gravity field and will be able to hop tens of meters above the surface by drawing its wheel struts together, then springing them outward. This would give the cameras and other instruments onboard a bird's-eye view of the asteroid terrain, and would allow the rover to cover much more ground overall. The weak gravity would pull the rover back to land gently on the surface. Solar panels on the rover's back and belly allow it an uninterrupted flow of electricity, no matter which way it lands. Like an agile cat, the rover is also equipped to right itself if necessary.
The MUSES-C spacecraft will carry a camera, an infrared spectrometer and a lidar instrument (a laser-based altimeter) that will be used by Japanese scientists and their NASA colleagues to study the asteroid from a distance of about 20 kilometers. An X-ray spectrometer will also be onboard to study the asteroid's bulk chemical composition. The NASA rover will carry a camera, an infrared spectrometer and an alpha X-ray spectrometer for analyzing the composition of the asteroid surface.
Up to three asteroid samples will be collected after small pellets are fired into the asteroid's surface. Ejecta from the pellets' impact will be collected through an inverted funnel and stored in a sample-return capsule onboard the orbiter. The capsule will parachute to Earth's surface when the orbiter re-approaches the planet in January 2006.
In addition to David Tholen, the scientists selected for the mission's U.S. team are:
Beth Clark of Cornell University, a UH alumna (PhD '93) who will use the rover camera and infrared spectrometer to study the physical and light-scattering properties of the surface of Nereus. This will aid in differentiating between data that characterizes the asteroid's chemical composition and data that shows optical effects of the surface.
Faith Vilas of the NASA Johnson Space Center, who will use the spacecraft infrared spectrometer to determine the nature of the minerals on the surface of Nereus through the comparison of spectral features with laboratory spectra of meteorites and terrestrial rocks.
Peter Smith of the University of Arizona, who will use the rover camera to study the surface characteristics of Nereus to understand how the surface and its structures evolved over time. Smith has worked with the cameras on numerous NASA missions including the Mars Pathfinder mission and the Cassini-Huygens mission to Saturn and Titan.
Andrew Cheng of the Johns Hopkins University Applied Physics Laboratory, who will use the spacecraft lidar (a laser-based altimeter) instrument to determine the size, shape, mass and rotation of Nereus. Cheng is the project scientist for NASA's Near-Earth Asteroid Rendezvous mission, which will encounter the asteroid Eros in February 2000.
Michael Zolensky of the NASA Johnson Space Center, who will participate in the preliminary petrologic, mineralogic, and compositional analysis of the asteroid samples returned to Earth by the MUSES-C spacecraft. Zolensky is a leader in the development and application of sample analysis techniques to extra-terrestrial samples and is a co-investigator on NASA's Stardust mission to collect a comet sample and return it to Earth.
The alpha X-ray spectrometer for the rover, which will be used to determine the chemical composition of many surface rocks, is being supplied by Thanasis Economou of the University of Chicago. Economou supplied a similar instrument for the Sojourner rover on the Mars Pathfinder mission and for many other NASA missions.
JPL is managing the U.S. contribution to the MUSES-C mission for NASA's Office of Space Science. For the NASA portions of the MUSES-C mission, Ross M. Jones of JPL is the NASA project manager, and Brian Wilcox of JPL is the lead engineer for the asteroid roving vehicle. The Institute of Space and Astronautical Science (ISAS) manages the MUSES-C project for Japan's Ministry of Education, Science, Sports and Culture, where Jun'ichiro Kawaguchi is the MUSES-C project manager and Akira Fujiwara the project scientist.