March 4, 1999
Vol. 18 No. 11

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    [anthony tuzzolini, bruce mckibben, and john simpson] by jason smith  Anthony Tuzzolino (left to right), Bruce McKibben and John Simpson were part of the Chicago team that designed the SPADUS instrument launched on ARGOS.

    Chicago scientists design SPADUS

    By Steve Koppes
    News Office

    Above the atmosphere, debris zips around the Earth at tens of thousands of miles an hour. Natural cosmic dust, produced by comets, meteoroid impacts or other natural processes explain some of the debris, while other objects are a result of human activity in space.

    The debris has caused varying levels of damage to space shuttles, satellites and the Hubble Space Telescope. And although detection systems currently track the largest pieces of man-made debris, there are still many more particles that are too small to track, ranging in size from pebbles or sand grains down to particles that can only be seen with a microscope.

    “Many of these particles are produced by collisions between larger debris objects, and so information about these particles is important for understanding the whole debris population in Earth orbit,” said Bruce McKibben, Senior Scientist at the University’s Laboratory for Astrophysics & Space Research.

    An instrument built at the University and designed to provide data to help reach that understanding was launched Tuesday, Feb. 23, on the Advanced Research and Global Observation Satellite, or ARGOS, from Vandenberg Air Force Base in southern California. ARGOS’s scientific payload includes the University’s space dust experiment known as SPADUS, which will measure the mass, speed and trajectory of dust particles in low-Earth orbit, and will allow scientists to determine whether they are particles left in the wake of comets or man-made orbital debris.

    “This is the first active experiment where you can separate these two phenomena,” said John Simpson, Chicago’s Arthur Holly Compton Distinguished Service Professor Emeritus.

    “We will be able to tell whether the debris is uniformly distributed or in clouds around the Earth, and even whether there’s a ring around the Earth, like Saturn’s, but very weak. This is one of the discovery possibilities.”

    ARGOS, an unclassified U.S. Air Force satellite, will circle the Earth for three years in a polar orbit at an altitude of 516 miles.

    In addition to the Chicago experiment, ARGOS will conduct high-temperature superconductivity experiments, perform upper atmospheric imaging and environmental studies, and test electric propulsion methods.

    SPADUS will measure the time of impact and the particle trajectory, as well as velocity of debris with enough sensitivity to detect particles smaller than those contained in a puff of cigarette smoke.

    Man-made debris in a circular orbit races about the Earth at speeds of nearly 17,000 miles an hour. “This debris consists of everything from rocket casings and dead satellites on down to the very small dust particles that can result from the grinding down of these large objects as they collide with each other and with dust particles already in orbit,” McKibben said.

    Cometary debris, on the other hand, travels more than 25,000 miles an hour. There is also a remote possibility that SPADUS will be able to detect dust particles entering the solar system from interstellar space.

    “They’ll have even higher velocities,” McKibben said. “Very small ones have been detected by spacecraft in the outer solar system right now. We might see them, but I wouldn’t count on it.”

    SPADUS will be used to study the Leonid meteor shower in November. The Leonid meteor stream consists of the boiled off remains of Comet Tempel-Tuttle and is usually fairly mild. But the shower was expected to be far more intense in 1998 and possibly 1999 because last February the comet made its closest approach to the sun, which happens once every 33 years.

    Last year, satellite controllers changed the orientation of their satellites to reduce surface exposure to the cometary stream. “The meteor shower was not as strong as some predictions in 1998, so maybe this year we’ll get the whole works,” Simpson said.

    Earth’s orbital path will take it across other cometary streams as well, said Anthony Tuzzolino, Senior Scientist at Chicago’s Laboratory for Astrophysics & Space Research. “There are 15 or 16 streams that are possible candidates for detection based on how close we’ll come to them,” he said. “There are a lot of things to look for.”

    Helping in the data analysis effort will be Herbert Gursky and his associates at the Naval Research Laboratory in Washington, D.C. The NRL contributed the instrument’s mechanical design and construction of the experiment housing.

    Similarly important contributions were made by Lockheed Martin, which provided the digital electronics box, including the microchips that make the sophisticated SPADUS measurements possible in a package small enough for space flight.