WIRE slowing down

Matson, Robert (ROBERT.D.MATSON@cpmx.saic.com)
Mon, 8 Mar 1999 13:55:10 -0800

Hi All,

NASA has issued an update on the WIRE status.  The
hydrogen cryogen has completely sublimed, so the sensor
is basically dead.  However, they are actively reducing
the spin rate which was as high as 1 rev/sec.  Report
indicates the current rate is ~41.7 revs/minute, and
falling by 0.5 revs/minute per orbit.  This means it
should take a little under a week to stablize.  --Rob

- - - - -

Don Savage
Headquarters, Washington, DC                      March 8, 1999
(Phone:  202 358-1727)

Lynn Jenner
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301 286-0045)

RELEASE:  99-37

WIRE SCIENCE INSTRUMENT RUNS OUT OF HYDROGEN

        Ground controllers are slowly gaining control of NASA's 
Wide-Field Infrared Explorer (WIRE), but the entire supply of 
frozen hydrogen needed to cool its primary scientific instrument 
has been released into space, ending the scientific mission of 
the spacecraft.

       "We are very disappointed at the loss of WIRE's science 
program," said Dr. Ed Weiler, NASA's Associate Administrator for 
Space Science at NASA Headquarters, Washington, DC.  "We are 
establishing a formal anomaly investigation board to find out 
what happened, which will help us to plan future missions.  I'm 
confident that many of the scientific goals can be accomplished 
by upcoming missions such as the Space Infrared Telescope 
Facility, so it will be science delayed rather than science 
lost."

       Spacecraft controllers believe the primary telescope 
cover was released about three days earlier than planned. As a 
result sunlight began to fall on the instrument's cryostat, a 
container of frozen hydrogen designed to cool the instrument. 
The hydrogen then warmed up and vented into space at a much 
higher rate than it was designed to do, causing the spacecraft 
to spin.  Controllers do not know what specifically caused the 
cover to be released.

     WIRE's primary instrument is a 30-centimeter aperture 
(12.5-inch) Cassegrain telescope enclosed inside a solid 
hydrogen cryostat.  The cryostat was designed to cool the 
telescope's inner workings to minus-430 degrees F -- cold enough so 
that the telescope's own heat emissions would not mask the 
infrared light that it is trying to detect in space.

      By early Saturday, the spacecraft's rate of spin had 
stabilized at about 60 revolutions per minute, giving 
controllers hope they could start the painstaking process of 
regaining control of the 563-pound spacecraft.  On Saturday, 
ground controllers developed and uploaded a new computer program 
to WIRE that began imparting small, countering forces using the 
satellite's onboard magnetic attitude control system to gently 
slow the spacecraft's spin. 

     Controllers have been successfully using this approach to 
slowly regain control of the spacecraft and reduce the spin rate 
approximately 3 degrees per second per orbit.  WIRE is now 
rotating about 250 degrees per second.  The objective is to 
reduce the spin rate sufficiently that the onboard system will 
take over and provide full attitude control. Controllers are 
hopeful this will be accomplished by the end of this week.

     "The spacecraft was never designed to be controlled in this 
manner," said Jim Watzin, Small Explorer Project Manager, "so 
it's slow, tedious work.  I'm confident by week's end we will 
have WIRE in a stable configuration, available for any analysis 
deemed appropriate."

     WIRE was launched March 4 at 9:57 p.m. EST from Vandenberg 
Air Force Base, CA. When the spacecraft made its second pass 
over one of the WIRE tracking stations, ground controllers 
determined that WIRE was spinning instead of maintaining a 
stable position in orbit, and temperatures for the cryostat and 
the instrument were warmer than expected.  

    After the anomaly investigation board completes its work 
with WIRE, engineers plan to use the spacecraft as an 
engineering testbed to evaluate advanced attitude control 
systems, communications, and data handling and operations.

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