NASA Satellite Duo Set for Cloud-Watching Mission
NASA's Cloudsat (upper left) and Calipso weather satellites show in this artist's rendition are set to launch into orbit next month.
Credit: NASA.

After months of delays, NASA is once again set to launch a pair of cloud-watching satellites to join a flotilla of probes aimed at improving weather and climate forecasts.

A Boeing-built Delta 2 rocket is due to launch NASA's CloudSat and CALIPSO satellites at 6:02:08 a.m. EDT (1002:08 GMT) on Friday in an early-morning space shot from Vandenberg Air Force Base in California.

"I know I speak for the entire team when I say it's been a long road," NASA's CloudSat project manager Kevin Brown, of the agency's Langley Research Center, in a Wednesday press briefing.

Originally delayed from a summer 2005 launch, CloudSat and CALIPSO were also unable to lift off last November due a labor strike by Boeing's aerospace workers. That strike ended in February 2006.

Now the two probes are set to join three others already in orbit and generate the first comprehensive, three-dimensional (3-D) views of Earth's clouds and extremely fine particles called aerosols. The data will not only aid weather studies, but also help researchers understand the impact humans have on Earth's climate and their contribution to global warming, mission scientists said.

"These satellite missions are experimental missions, they're firsts," said Hal Maring, NASA's CloudSat and CALIPSO program scientist at the agency's Washington D.C. headquarters, during the briefing. "If these missions are successful, as I believe they will be, they could be the foreshadowing of operations or routine measurements that could come later."

A radar eye

At the heart of the CloudSat and CALIPSO is their ability to generate 3-D views of Earth's cloud and aerosols, where past spacecraft have made primarily two-dimensional observations.

For CloudSat, a $185 million mission aboard a 1,870-pound (894-kilogram) satellite, that capability is centered on a powerful radar designed not only to build a 3-D map of cloud cover, but also identify specific particles of clouds, rain and snow to pinpoint how water is globally distributed in the Earth's atmosphere.

"The CloudSat radar will be about 1,000 times more sensitive than your regular radar," said David Hudak, a mission research scientist with the Science and Technology Branch of Environment Canada, during the briefing.

Graeme Stephens, CloudSat's principal investigator at Colorado State University in Fort Collins, said the satellite will allow scientists to quantify the contribution of cloud cover to the global greenhouse effect and make fundamental observations into the Earth's water cycle.

"We haven't seen Earth like this before," Stephens said. "There's going to be much discovery to come from thee new missions."

Laser vision

Where CloudSat has a radar, CALIPSO has a laser.

Short for the hefty title Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations, CALIPSO uses a laser ranging instrument - or lidar - to measure the levels and characteristics of aerosols in Earth's atmosphere.

The $223 million CALIPSO mission is a joint effort between NASA and the French Space Agency (CNES) featuring a 1,294-pound (587-kilogram) spacecraft that carries three primary instruments. In addition to the lidar, the satellite is equipped a wide-field visible light camera and an imaging infrared radiometer to study the atmosphere's aerosol content.

"In many ways, clouds and aerosols...affect and in some way even control climate, weather climate, the air we breathe and the water we drink," Maring said.

Variations in the amount of natural and human-made aerosols in the Earth's atmosphere can affect temperatures and contribute to the greenhouse effect and global warming, researchers said.

"It's very important to know what the human impact on the aerosol content is," said Jacques Pelon, CALIPSO co-principal investigator at France's Institute Pierre Simon Laplace, during the briefing.

Late for the 'A Train'

CloudSat and CALIPSO are relative latecomers to a series of Earth watching satellites working together to build a comprehensive picture of the planet's weather and climate.

Scientists have dubbed the spacecraft group the 'Afternoon Train' - or 'A Train' - since it crosses the equator during the early afternoon. All of the satellites are aimed at an orbit 438 miles (705 kilometers) above Earth.

First in the group is NASA's water-watching Aqua satellite launched in May 2002, which was followed by the space agency's Aura spacecraft in July 2004. A third satellite, France's PARASOL spacecraft studying the microphysical properties of clouds and aerosols, launched in December 2002.

"The value of this combined set of measurements gives us hope to be able to constrain the Earth's system...to the point of being able to predict it," Maring said. "And prediction is terribly important."