RHESSI News Item

Dolores Beasley
Headquarters, Washington, DC March 24, 2000
(Phone: 202/358-1753)

Mark Hess
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-8982)

Mary Beth Murrill
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-6478)

RELEASE: 00-45


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, ten 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 

Following its release from the vibration facility, the HESSI 
team will disassemble the spacecraft, 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 Pegasus 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 

More information on the HESSI mission can be found on the 
Internet at: