UC Berkeley press release


Lewis satellite to carry UC Berkeley experiment into orbit for atmospheric imaging and mapping of the interstellar medium

by Robert Sanders

AT 11:51 P.M. PDT FRIDAY, AUGUST 22, 1997

Berkeley -- NASA is scheduled to launch by the end of May one of its new "faster, cheaper, better" satellites carrying two Earth-imaging instruments plus a UC Berkeley instrument with a dual purpose -- to study the Earth's upper atmosphere and to map extreme ultraviolet emissions in space.

The Lewis satellite and its companion, Clark, scheduled for launch later this year, are part of NASA's new Small Spacecraft Technology Initiative meant to shorten the time between project conception and launch, and by putting much of the design work in the hands of private companies, decrease the cost.

Lewis will be inserted into a 525-kilometer high orbit by a new Lockheed Martin Launch Vehicle (LMLV-1) launched out of Vandenburg Air Force Base in California.

The Ultraviolet Cosmic Background experiment, built by the Space Astrophysics Group at UC Berkeley's Space Sciences Laboratory, is designed to study the interstellar medium, the thin material between the stars. UC Berkeley astronomer Stuart Bowyer and his team discovered a hot component of the interstellar medium in the 1960s which was the first indication that some of the gas in the interstellar medium has a temperature of over a million degrees.

The experiment will search the night sky for the signature of this million-degree material, concentrating on the extreme ultraviolet (EUV) band of the spectrum between X-rays and the ultraviolet. The instrument will obtain measurements which are 1,000 times more sensitive than any made previously in this band, and will provide substantial new information about the character of the hot interstellar medium, says Bowyer, a professor in the graduate school at UC Berkeley and principal investigator on the project.

"The spectrometer is designed to make measurements of the glow of hot gas between the stars," he says. "One of the main goals is to search for the signature of the million-degree material, which is still not understood and is the subject of much controversy."

The spectrometer also will provide new information on the character of the Earth's upper atmosphere. As the satellite moves from daylight through twilight into orbital darkness, the instrument will look for the signature of atoms and ions evaporating from the outer edge of Earth's atmosphere, as a way to determine their density and extent of ionization.

Other instruments aboard the satellite are a TRW-built Hyper-Spectral Imager for Earth observation and commercial remote sensing, and a Linear Etalon Imaging Spectral Array (LEISA) for scanning the Earth and its horizon. LEISA was built at NASA's Goddard Space Flight Center in Houston.

According to NASA, the applications for instrument data are far-reaching. They include agriculture, forestry, environmental assessment, regional planning, urban analysis, plant and ocean biology, geology, polar climatology and astrophysics.

UC Berkeley's instrument will advance astrophysics and space science too, Bowyer says. One very speculative but intriguing possibility, for example, is that the spectrometer will find the signature of decaying neutrinos -- tenuous particles of the nuclear zoo which some cosmologists have theorized are providing the necessary gravitation to hold our galaxy together. A number of attempts have been made to test this theory, but none have been conclusive. The experiment will provide data which will definitively prove or disprove this theory.

Jerry Edelstein, project scientist based at UC Berkeley's Space Sciences Laboratory, says the spectrometer achieves its extraordinary sensitivity through a variety of means. For example, it employs a new spectrograph invented by the Berkeley group to optimize sensitivity to the diffuse EUV emission from regions between the stars. It also uses innovative technology to achieve a small, lightweight and highly reliable instrument.

The spectrometer was developed and integrated into the Lewis Spacecraft with funds provided by NASA, TRW and the UC Berkeley team.

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