No, this isn’t that Alan Bean story.

It’s March 5, 1999. Orbital Sciences (now Orbital ATK) has been enjoying improved success with its special air-launched rocket, the Pegasus XL. Dropped from a modified jetliner around 40,000 feet (12 km), the three to four-stage solid-propellant Pegasus flies payloads up to 933 pounds (433 kg).

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Pegasus dropped for launch. (NASA)

That doesn’t sound like a lot of payload. But this is the age of microsatellites: Satellites so finely designed but packed with small but powerful instruments that they take up far less space and mass than satellites made decades before. And Pegasus, not requiring a launch pad or liquid fuel tanking, is a competitively-priced LEO launch vehicle, also able to launch satellites flexibly into polar as well as equatorial orbits.

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A replica of Pegasus XL. (Credit: Smithsonian National Air and Space Museum)

That day, Pegasus carries one of its more prestigious payloads: A NASA astronomy satellite called the Wide-Field Infrared Explorer, or WIRE. It was intended to make some serious infrared studies of the universe and specific galaxies.

To make those observations, WIRE was built with a special telescope that was highly sensitive to heat signatures. The telescope was cooled by a hydrogen-based cryostat, a device that recirculates super-cooled gases around a structure. Provided that the telescope was not subjected to intense light that would overheat the instrument, the telescope would be fine.

Protecting the telescope optics was a dust cover that would be ejected at the right time when the telescope was pointed at deep space. Over the 4 month mission, the slow sublimation of the solid hydrogen in the cryostat would be ejected gradually through a small vent on the device.

Okay, maybe this is like an Alan Bean story.

Pegasus placed the satellite right where it was supposed to be, over 290 miles (470 km) in polar orbit to begin its 4 month mission. But there was a failure in the spacecraft’s pyro actuator control hardware. This device was an off-the-shelf device that the satellite designers trusted but didn’t customize or test sufficiently for their needs.

On orbit, WIRE’s telescope was intentionally pointed towards Earth to safe it against intense sunlight while the spacecraft was checked out from the ground. But that idea assumed the dust cover was still present.

The fault in the pyro electronics had jettisoned the dust cover prematurely a short time after reaching orbit, exposing the highly sensitive telescope to earthshine, and thus more heat than it could handle.

The cryostat tried to keep the telescope cool but it became so hot that the cryostat itself began to heat up so rapidly. Making matters worse, the tiny vent on the cryostat for use over 4 years of normal cooling had begun to blast out enough hydrogen to turn itself into a tiny thruster.

WIRE began a rapid spin as fast as 60 revolutions per minute along its center body.

By the time ground controllers got WIRE under control, the damage was done. WIRE’s cryostat was depleted, and the sensitive telescope was toasted.

The satellite did have secondary instruments it could use for other experiments. So the four-month mission turned into an over one-year mission making astroseismology studies, watching how stars oscillate to gather more data about their composition.

WIRE was later decommissioned and later deorbited in 2011. A successor satellite, the aptly-named Wide-Field Infrared Survey Explorer (WISE), a much-larger spacecraft launched a decade later in 2009 on a Delta II rocket, completed the mission, also being one of the early satellites to find boat-loads of minor planets and new galaxies. Today, WISE still works as a near-earth asteroid detector, reactivated as NEOWISE.

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