NASA's CloudSat, CALIPSO Satellites Begin Cloud-Watching Mission
NASA's CloudSat and CALIPSO spacecraft launch spaceward from California's Vandenberg Air Force Base on April 28, 2006 after six days of delays.
Credit: NASA.

After a week of launch scrubs, poor weather and other delays, two NASA satellites successfully reached orbit Friday to begin their mission to scan the Earth's clouds in three dimensions.

NASA's CloudSat and CALIPSO spacecraft successfully launched spaceward atop a Boeing Delta 2 rocket at 6:02:16 a.m. EDT (1002 GMT) from Vandenberg Air Force Base in California. The space shot comes after six days of delay caused by glitches, refueling plane schedules, high winds and poor weather.

"When we lifted off you could just feel the release," NASA launch director Chuck Dovale said after CloudSat's deployment. "Not only in watching the vehicle on the pad, but the release of the folks here in the launch center."

The two spacecraft are expected to produce unprecedented views of Earth's clouds and aerosols - fine particles suspended in the atmosphere - that can be used to track climate change and improve weather forecasts, mission scientists said.

Clouds and climate change

CloudSat's $185 million mission calls for the probe to peer through Earth's clouds using a powerful radar 1,000 times more sensitive than typical instruments to identify individual particles of clouds, rain and snow.

"Clouds fundamentally influence the greenhouse [effect] of the climate," said Graeme Stephens, CloudSat's principal investigator at Colorado State University in Fort Collins, before today's launch, adding that Earth's water cycle sets the pace for greenhouse gases and global warming. "CloudSat is trying to get a handle on the key aspects of that water cycle."

The $223 million CALIPSO - short for or Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations - carries a laser ranging, or lidar, instrument and two other tools to identify and characterize aerosol distribution in the Earth's atmosphere. The spacecraft is a cooperative effort with the French Space Agency (CNES).

CloudSat and CALIPSO were deployed - CALIPSO first - in a 438-mile (705-kilometer) orbit where they are expected to join three other spacecraft already in orbit. Together with NASA's Aqua and Aura satellites, as well as France's PARASOL spacecraft, CloudSat and CALIPSO will make the "Afternoon Train" (A Train) of Earth-observation, mission managers said.

Rocky road to space

Friday's space shot not only marked the beginning of the joint CloudSat and CALIPSO missions, but also the end to almost a week of flight delays for the beleaguered satellite pair.

"It was a quite difficult mission almost from start to finish," Dovale said of the launch. "We had quite a few scrubs and in between we days where we called things off early."

An initial April 21 launch attempt was thwarted with just 48 seconds left before liftoff after CALIPSO lost communications with its support center in France. Flight controllers quickly reestablished the communications link, but missed the split-second launch window that day.

Launch opportunities on Saturday and Sunday were plagued by a different ailment: the unavailability of a refueling plane needed to supply a radar tracking aircraft that monitored today's liftoff as the Delta 2 rocket carried CloudSat and CALIPSO out of range of flight controllers on the ground.

High winds cropped up four minutes before a Tuesday launch attempt, scrubbing the attempt, while a poor weather outcast prevented a Wednesday launch outright.

The final scrub occurred early Thursday, when a temperature sensor returned errant readings that prompted engineers to call off the launch and look into the matter. The issue was later resolved and the launch attempt shifted to Friday.

"This was technically the fourth attempt...a great success," Dovale said.