Donald Savage
Headquarters, Washington                    July 21, 2003
(Phone: 202/358-1547)

Nancy Neal
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301/286-0039)

RELEASE: 03-243

NASA TEAM GIVES FUSE SPACECRAFT TRIPLE BRAIN TRANSPLANT

     NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) 
satellite was given a new lease on life following the 
successful implementation of new software in three computers 
that work together to control the precision pointing of the 
telescope.

"We have uploaded new flight software, and can operate FUSE 
with any number of gyroscopes, including none, if the time 
comes that all of our gyroscopes fail," said Dr. George 
Sonneborn, FUSE project scientist from the NASA Goddard 
Space Flight Center (GSFC), Greenbelt, Md. "This is a 
significant conceptual and technical development that brings 
a new tool to the designers of new and existing satellites, 
and bodes well for continued FUSE operations," Sonneborn 
added.

For the past two years, engineers and scientists at the 
Johns Hopkins University (JHU) in Baltimore, Orbital 
Sciences Corporation in Dulles, Va., Honeywell Technical 
Solutions, Inc., Morris Township, N.J., GSFC, and the 
Canadian Space Agency, Quebec, have worked together to 
change the flight software used to point the telescope for 
science observations. 

This involved changing the software aboard all three 
spacecraft computers: the Attitude Control System, the 
Instrument Data System, and the processor on the Fine Error 
Sensor guide camera, provided by the Canadian Space Agency. 
After extensive testing, the new software, for all three 
computers, was up linked to the satellite in mid-April 2003.

"I would compare this procedure to performing a brain 
transplant on a living satellite, but it's more like a 
triple brain transplant," said Dr. William Blair, FUSE chief 
of observatory operations and a research professor at Johns 
Hopkins University. "All three computers have to talk and 
work together properly to make it all work," he said.

Testing on this new configuration has been ongoing since 
April, even as normal science observations have been carried 
out. FUSE can operate on as few as zero gyroscopes, with no 
degradation in science data quality and only a slight loss 
of observation scheduling efficiency.

The gyroscopes on board FUSE do not move the satellite, but 
they provide information on how the spacecraft is moving or 
drifting over time. FUSE has two packages of three ring-
laser gyroscopes. Until the new software was loaded, one 
operating gyroscope on each of the three axes was needed to 
conduct normal science operations. FUSE still has this 
needed configuration, but there has been concern about how 
long the gyroscopes could last. One gyroscope failed in May 
2001, and the five remaining gyroscopes all show signs of 
age.

FUSE has already survived the loss of two of its four 
reaction wheels in late 2001. The reaction or momentum 
wheels are devices that normally allow the satellite to be 
held steady or moved from one pointing direction to another. 
Through quick thinking, engineers and scientists modified 
control software to use devices, called magnetic torquer 
bars, to provide stability in place of the missing reaction 
wheels. These devices interact with the Earth's magnetic 
field to provide a stabilizing effect on the satellite.

The FUSE satellite, launched in June 1999, is a space 
telescope that performs high-resolution far-ultraviolet 
spectroscopy of a broad range of astronomical objects. FUSE 
observes light at shorter wavelengths than the Hubble Space 
Telescope can observe, thus providing a complementary 
capability. Because it has survived a number of close calls, 
but is still returning excellent science data, the team 
sometimes refers to FUSE as "the little satellite that 
could."

Looking ahead, NASA has just released the call for proposals 
for new observations with the satellite, during its fifth 
year of operations, by astronomers from around the world.

The JHU manages FUSE for GSFC and the Office of Space 
Science at NASA Headquarters in Washington. Partners include 
the JHU Applied Physics Laboratory, the Canadian Space 
Agency, the French Space Agency, Honeywell Technical 
Solutions Inc., and primary spacecraft contractor Orbital 
Sciences Corporation.

For more information about NASA on the Internet, visit:

http://www.nasa.gov

For more information about FUSE on the Internet, visit the 
mission home page:

http://fuse.pha.jhu.edu

-end-

                            * * *