NASA's High Energy Solar Spectroscopic Imager spacecraft -- an international mission to explore the basic physics of particle acceleration and energy release in solar flares -- has sustained substantial damage during vibration testing. Repairs to the spacecraft, known as HESSI, will likely delay its launch to no earlier than January 2001.

The damage was caused when a test device that simulates vibrations the spacecraft can expect during launch delivered approximately 20G's, 10 times the appropriate levels for the test. As a result, the spacecraft's structure was damaged and two of the four solar arrays were cracked. The status of the HESSI instrument is not currently known.

Engineers are optimistic that the structure, instrument boxes and detectors were not harmed, but further analysis will be required to determine the full extent of the damage. Both damaged solar arrays need to be replaced.

The incident occurred March 21 while the spacecraft was undergoing vibration testing in facilities at NASA's Jet Propulsion Laboratory, Pasadena, CA.

The spacecraft and vibration facility are impounded pending an independent failure review board that will be chaired by NASA's Marshall Space Flight Center, Huntsville, AL, and supported with experts from NASA's Goddard Space Flight Center, Greenbelt, MD; NASA Headquarters, Washington, DC; and other NASA centers as required. This board will begin investigating in the next several days, and is expected to conclude its efforts in six to eight weeks.

After the spacecraft is released from the vibration facility, the HESSI team will disassemble it, re-inspect it, and perform needed repairs. It is expected replacement of the solar arrays will take four to six months.

HESSI was scheduled to be launched on a Pegaus rocket in July 2000. While a new launch date is not known, current estimates, depending on the amount of work that will have to be done, put a launch no earlier than January 2001. The cost to repair the satellite, which will determine how long the mission will be delayed, has not yet been determined. NASA's cost for the HESSI spacecraft was budgeted at $40 million. Development, launch vehicle and mission operations costs bring the total mission value to $75 million.

HESSI is a Small Explorer mission and is managed by Goddard under the Explorer Program. The science team includes co- investigators from Switzerland, Scotland, Japan, France and the Netherlands.

More information on the HESSI mission can be found on the Internet at or .

News Media Contact

Mary Beth Murrill, JPL, (818) 354-6478

Dolores Beasley, NASA Headquarters, Washington, D.C., (202) 358-1753

Mark Hess, NASA Goddard Space Flight Center, Greenbelt, MD, (301) 286-8982