NASA Headquarters, Washington, DC

March 19, 1998

TWO STUDIES WILL REFINE AND EXPAND SOLAR MONITORING TASK

The Naval Research Laboratory, Washington, DC, and the University of Colorado's Laboratory for Atmospheric and Space Physics in Boulder have been selected by NASA's Office of Earth Science to conduct parallel six-month definition studies of a new small satellite to monitor variations in the amount of radiant solar energy that reaches Earth.

The precise measurements to be obtained by the Total Solar Irradiance Mission (TSIM) will help scientists better understand the relationship between the Sun's variable energy output and its effects on Earth's climate. The six-month feasibility studies will focus on the development of a preliminary system design and operations concept for the cost- capped $23 million mission.

NASA has been measuring the total radiative output of the Sun from the unique perspective of space since the late 1970s. The current sensor being used is called the Active Cavity Radiometer Irradiance Monitor (ACRIM). NASA has flown two ACRIM instruments, including the ACRIM-II instrument onboard NASA's Upper Atmosphere Research Satellite. A third ACRIM instrument is scheduled for launch aboard a dedicated small satellite in October 1999.

TSIM will extend the broad data set gathered by the ACRIM series while exploring a new capability to measure solar irradiance in two discreet spectral bands. Once proven, this operationally oriented capability is a candidate for flight aboard future National Polar Orbiting Environmental Satellite System missions being planned by a tri-agency partnership among NASA, the Department of Defense and the National Oceanic and Atmospheric Administration.

"TSIM will be developed in 36 months or less using the same key principles of 'faster, better, cheaper' spacecraft demonstrated by the agency's Discovery Program," said Dr. Ghassem Asrar, NASA Associate Administrator for Earth Science. "We hope to obtain an instrument payload that is lighter and more technologically advanced, yet provides an exciting additional capability that will give us new knowledge about our climate and why it varies."

TSIM is part of NASA's Earth Observing System, a series of advanced remote-sensing satellites designed to provide simultaneous measurements of a broad range of physical, chemical and biological processes to enable researchers to study the Earth's land, oceans, air, ice and life as a total system. TSIM also will serve as NASAÕs contribution to the joint small Science Satellite (SciSat) program with the Canadian Space Agency. NASA and Canada have committed to developing independent science research missions to be launched on a NASA-funded launch vehicle in December 2001, with shared data after launch.

The two selected teams will document their analyses for NASA review by the end of 1998, with one team being selected to proceed with development. TSIM program management will be provided by NASA's Goddard Space Flight Center in Greenbelt, MD.

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