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Tuesday, March 9, 1999 Published at 11:50 GMT


Sci/Tech

Satellite mission destroyed

The satellite had "landmark" new cooling and imaging technology

The scientific mission of a Nasa satellite has failed before it even started.

The $79m Wide Field Infrared Explorer (Wire) has lost all its liquid hydrogen into space.

Without the cooling fluid, its telescope cannot detect infrared radiation. This was the sole objective of the mission, designed to learn more about how galaxies form and evolve.

"We are very disappointed at the loss of Wire's science program," said Dr Ed Weiler, Nasa's Space Science chief in Washington DC.

"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 not lost," he said.

Hot problem

The spacecraft controllers believe that a cover was opened about three days earlier than planned. This allowed sunlight to fall on the container of frozen hydrogen designed to cool the instrument.


[ image: WIRE intended to capture an infra-red map like this]
WIRE intended to capture an infra-red map like this
The hydrogen warmed up, increasing pressure in the tank, and vented into space at a much higher rate than normal. The controllers were unable to stop the entire load of hydrogen pouring out into space.

The reason why the cover was opened is not known and an investigation has been launched.

A literal spin-off of the hydrogen squirting out of Wire was to set it revolving out of control. The spacecraft's rate of spin stabilised on Saturday at about 60 revolutions per minute.

Controllers fought to regain control of the spacecraft by sending up a computer program that started small, countering forces using the onboard magnetic attitude control system. This gently slowed the spacecraft's spin, but too late for the mission to be saved.

On Tuesday, the rate of spin was about 40 revolutions per minute. Controllers hope that by the end of the week the spinning will be reduced further, so that the on board system can take over and keep the satellite steady.

Rapid failure

Wire's problems became apparent very shortly after its delayed launch at 0257 GMT on 5 March from Vandenberg Air Force Base, California. The high temperatures and spinning were spotted when the spacecraft made only its second pass over one of the tracking stations.


[ image: The detector needed to be kept super-cold to trap infra-red rays]
The detector needed to be kept super-cold to trap infra-red rays
After the investigation, Wire will become an engineering test-bed for control systems, communications and data handling.

The loss of the cooling hydrogen was disastrous to Wire because detecting faint infrared rays is equivalent to feeling tiny traces of heat. If the spaceship is too warm, its heat will swamp its own detectors.

A temperature of -260 degrees centigrade was needed to capture the dim glow of distant stars.

At 260kg (570lb), Wire was one of the smallest scientific satellites ever to be put into space. It was to watch galaxies being born and then changing by following the formation of stars in distant parts of the Universe.



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