University instrument headed for Saturn's rings

By Diana Steele
News Office

When NASA's

International Cassini

spacecraft begins winging its way toward Saturn later this month, it will carry on board an instrument -- designed and built at the University's Laboratory for Astrophysics & Space Research of the Enrico Fermi Institute -- that will delve into the mysteries of Saturn's rings. The launch is currently scheduled for Monday, Oct. 13, and the spacecraft will reach Saturn in June 2004, after a seven-year interplanetary voyage.

The instrument is the second one designed by LASR scientists used in space exploration this year. The Alpha Proton X-ray Spectrometer, carried by the Sojourner rover, continues to examine the surface of Mars, analyzing the chemical composition of Martian rocks and soil, as part of the Pathfinder mission (see Sept. 25 Chronicle).

The latest University-built instrument, the High Rate Detector, is part of the Cosmic Dust Analyzer, from Germany, which will collect and analyze the dust particles in the interplanetary space and major components of the Saturnian ring system. The HRD is capable of collecting and analyzing 100,000 particles per second, and it will determine the size and mass distribution of particles in the rings that range from 0.1 micron to more than 100 microns in diameter.

The HRD was created by Anthony Tuzzolino, Senior Scientist in the Enrico Fermi Institute, under the direction of John Simpson, the Arthur Holly Compton Distinguished Service Professor Emeritus in Physics, a veteran space researcher who has prepared instruments for nearly 40 spacecraft.

"One big question that hasn't yet been answered is how the rings actually formed, whether they are leftovers from planetary formation, at the one extreme, or accretions of material from outer space, at the other," Simpson said.

According to Tuzzolino, the HRD will allow scientists to tell the mass distribution of the particles in the rings and "get an idea of which of the many theories of ring formation might be correct."

Cassini is the first satellite mission to orbit Saturn, and it will make 60 tours of the planet over four years, from 2004 to 2008. On board the spacecraft is a small probe, Huygens, designed by the European Space Agency, which will be released to descend to the surface of Titan, Saturn's largest moon and the only one with an atmosphere. Other instruments, from several nations, on Cassini will probe Saturn's magnetosphere, take close-up pictures of other Saturnian moons and map the surface of Titan.

Cassini's journey to Saturn includes two gravity-assist fly-bys of Venus and one each of Earth and Jupiter, which will give the spacecraft added momentum to reach its distant goal.

Instruments similar to the HRD and built by University scientists flew on Vega 1 and 2, Russian spacecraft that visited Comet Halley in 1986 to gather information about the size distribution of the dust emitted from the comet's coma. Similar instruments also will be part of two missions scheduled for launch in 1998 and 1999: the ARGOS mission to measure orbital debris above Earth's atmosphere and assess the optimal orbits for satellites and the planned space station, and the Stardust mission to Comet Wild 2.

Although many instruments aboard Cassini will be collecting data en route to Saturn, the Chicago instrument won't play its starring role until 2004, when the spacecraft reaches Saturn's rings.

"We'll be looking for an advanced student to work on this project when we start collecting data, but he or she is probably still in high school right now," Simpson said, laughing. "Everybody in the lab has to write very clearly in their notebooks so that someone can read it a decade from now."

At age 80, Simpson has helped create instruments on board three dozen spacecraft after witnessing the dawn of the space age as one of the organizers of the International Geophysical Year in 1957. In 1962 he founded the University's Laboratory for Astrophysics & Space Research.

"In the early 1960s, we were the first to develop solid state sensors for use in space," said Simpson. "Up until then, they were notoriously unreliable, and our success led to many spinoffs. We invent and then execute new space experiments, and then others pick it up."

Simpson and his colleagues' exploration of the solar system spans from Pioneer 2 in 1958 to Ulysses, which is currently conducting a study over the north and south poles of the Sun. Their scientific accomplishments include the determination of the age of our galaxy's cosmic radiation (20 million years), explorations of the size and nature of the Sun's heliosphere of radiation and charged particles, and study of planetary magnetospheres in the Solar System.