May 7, 2009

CALIPSO switches to back-up laser

After 3 years operating flawlessly, the French-US satellite’s laser has failed. This contingency had been expected and CALIPSO has successfully switched to its back-up laser.

Slow canister leak

We designed the system with the ability to change to a back-up laser," said Chip Trepte, CALIPSO* project scientist at NASA's Langley Research Center. The laser is the satellite’s eye, enabling CALIPSO to obtain vertical profiles of Earth’s atmosphere.

CALIPSO’s mission is to better understand the role of clouds and aerosols (suspended particles from fires, industrial activities and natural processes) in climate change.

But without its laser, CALISPO is blind. “Early this year the laser started showing unstable behaviour consistent with low canister pressure,” explains Nadège Quéruel, CALIPSO mission operations manager at CNES. “We therefore decided to turn on the back-up laser.” This was an eventuality that NASA and CNES teams had been prepared for.

We were aware before launch in 2006 that the pressure canister that housed the primary laser had a slow leak,” says Nadège Quéruel. “But we were sure that it could still complete the three-year prime mission.”

10-day gap in data

The primary laser performed as expected but could not survive the hostile conditions of space any longer. Its back-up laser is now operational and the satellite has resumed returning its precious data since 12 March.

CALIPSO is part of the A-Train constellation with 4 other satellites. Credits: NASA.
CALIPSO is part of the A-Train constellation with 4 other satellites. Credits: NASA.

The good news is we turned on the second laser that had been idle for 3 years, and it's working as well as the primary laser did early in the mission,” Trepte said. “The pressure in the second laser canister is quite high, and it should be able to operate for many more years.”

The back-up laser will therefore assure continuity of CALIPSO data and the total gap in data products as a result of the transition should not exceed 10 days.

CALIPSO's observations complement data recorded by the 4 other satellites flying in formation called the A-Train, which provide an unprecedented comprehensive global view of Earth’s atmospheric chemistry.

*Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations

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