BERKELEY - The long-delayed launch of a UC Berkeley/NASA satellite to study violent explosions on the sun is now set for next Tuesday, Feb. 5, from the belly of an Orbital Sciences Corp. plane over the Atlantic Ocean.

The High Energy Solar Spectroscopic Imager, or HESSI, designed, built and operated by an international consortium led by scientists at the University of California, Berkeley, will embark on a two- to three-year mission to look at high-energy X-ray and gamma ray emissions from solar flares. Though various satellites have made X-ray and gamma ray observations of flares, which are enormous explosions in the solar atmosphere, HESSI will be the first to snap pictures in gamma rays and the highest energy X-rays.

HESSI was originally scheduled for launch in July 2000, but was postponed after the satellite suffered damage during vibration testing. Since then, flight delays due to launch vehicle failures have affected the launch date. However, officials have since cleared the way for next Tuesday's scheduled launch.

Robert P. Lin, professor of physics in the College of Letters & Science at UC Berkeley and principal investigator for the mission, is optimistic that HESSI will achieve its original scientific goals.

"We were aiming for the peak of solar activity in mid-2000, so we have been lucky that, with the slip of our launch date by a year and a half, solar activity has continued to stay high," Lin said. "The sun had another peak of activity at the end of 2001. We still think we will image around a thousand solar flares, though whatever we see will be new and interesting."

HESSI, whose total mission cost is $85 million, is the sixth Small Explorer (SMEX) spacecraft scheduled for launch under NASA's Explorers program.

PRE-LAUNCH EVENT - MONDAY, FEB. 4

NEWS CONFERENCE, 2-3 p.m. EST

WHAT: At Kennedy Space Center, a combination mission and science briefing. Participants will discuss the overall mission, the launch vehicle, spacecraft health, and timeline between separation from the Pegasus rocket through start of science operations. Scientists will discuss details of the science payload and science objectives for the mission. NASA will provide live broadcast via NASA-TV. The news conference also will be streamed through the web from the KSC Web site at http://www.ksc.nasa.gov/.

WHO: Robert P. Lin, UC Berkeley principal investigator for HESSI Brian Dennis, HESSI mission scientist at Goddard Bill Wagner, NASA's Sun-Earth Connection program manager

NOTE: West Coast reporters may view the Florida news briefing from the conference room at the University of California, Berkeley's Space Sciences Laboratory beginning at 10:30 a.m. PST. Several HESSI scientists will be at the lab. The lab is at the top of Centennial Drive near its intersection with Grizzly Peak Boulevard. Please check in at the front office for parking permit.

LAUNCH DAY EVENTS - TUESDAY, FEB. 5

FROM KENNEDY SPACE CENTER.

WHAT: Live NASA-TV coverage and commentary of the HESSI launch, including L-1011 take-off from Cape Canaveral, Fla., and drop of the Pegasus rocket. The launch as seen from a chase plane will be on NASA-TV or on the Web at http://www.ksc.nasa.gov/.

WHEN: Coverage begins at about 2:00 p.m. EST. L-1011 take off is at 2:30 p.m., with Pegasus drop scheduled for 3:26 p.m. EST.

FROM UC BERKELEY

WHAT: Viewing of the launch at UC Berkeley's Space Sciences Laboratory via live satellite feed from NASA-TV. HESSI scientists in the Mission & Science Operations Center (MSOC) will provide regular updates. The main update will be given after the satellite's first pass over Berkeley, at about 2 p.m. PST. By then, HESSI scientists should have information about the health of the spacecraft.

WHO: Robert P. Lin, HESSI principal investigator, UC Berkeley professor of physics, director of UC Berkeley's Space Sciences Laboratory Manfred Bester, lead scientist in HESSI Mission Operations Center, UC Berkeley David Smith, spectrometer development scientist, UC Berkeley

WHEN: 10:30 a.m. - 3 p.m. PST

WHERE: Conference room, first floor of Silver Laboratory Addition, UC Berkeley.