A NASA satellite the size of a small piano shot into space Wednesday atop an air-launched rocket, kicking off a two-year mission to study odd clouds high above Earth that shine brightest at night.

The U.S. space agency's Aeronomy of Ice in the Mesosphere (AIM) spacecraft rode an Orbital Sciences-built Pegasus XL booster into to orbit at 4:26 p.m. EDT (2026 GMT, 1:26 p.m. PDT), after falling free from its parent aircraft while flying 39,000 feet (11,887 meters) above the Pacific Ocean.

"It was nominal, the spacecraft is power positive, the solar arrays are deployed and we're in the right place," NASA launch director Omar Baez said after the satellite reached orbit. "You can't call it any better than that."

The probe began its Wednesday space shot at California's Vandenberg Air Force Base, where its Stargazer L-1011 parent aircraft took off towards an airborne launch zone.

NASA's AIM spacecraft is designed to seek out and study noctilucent - or 'night shining' - clouds, odd collections of ice crystals that form near the edge of space some 50 miles (80 kilometers) above Earth's polar regions. The clouds form so high above Earth that they reflect sunlight after the Sun has dipped below Earth's horizon.

But while the phenomena were first observed in 1885, researchers still don't know how the clouds form, why they vary and their connections to Earth's changing climate or the Sun's energy.

"They are increasing in frequency. They are getting brighter and are appearing at lower latitudes than before," AIM principal investigator Jim Russell, of Virginia's Hampton University, said of AIM's cloudy quarry Wednesday just before launch. "We need to know why it's happening and what the relationship is to global climate change and to what we're doing to our atmosphere."

The $140 million AIM mission is the latest addition to NASA's Heliospherical Observatory, a constellation of now-16 different spacecraft studying the Sun's influence and interactions with Earth and the rest of the solar system.

"This system cannot be studied using a single, isolated satellite," AIM program scientist Mary Mellott, of NASA's Washington, D.C.-based headquarters, said before launch.

Researchers at Hampton University are overseeing the mission for NASA's Goddard Space Flight Center in Greenbelt, Maryland.

High-flying clouds

The Orbital Sciences-built AIM satellite carries three primary instruments aboard its 430-pound (195-kilogram) frame to study noctilucent clouds, which are also known as Polar Mesospheric Clouds (PMCs).

A multitude of onboard cameras will photograph the clouds from different angles, while other instruments study the role of atmospheric temperatures and the role of cosmic dust to their icy formation. The Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, which built two of AIM's instruments, will control the spacecraft during its two-year mission. Researchers at Utah State University also built one of AIM's science tools.

"AIM is the first mission dedicated to the study of noctilucent clouds," Russell said Tuesday in a prelaunch briefing. "We've had other clouds make measurements, but they have been serendipitous."

Noctilucent clouds were first observed following the Krakatoa volcano eruption, and some researchers believe their increasing frequency may be associated with global warming.

Russell said the build-up of carbon dioxide in the atmosphere, which leads to warmer temperatures near the Earth's surface, can cause colder conditions at high altitudes that are ripe for noctilucent cloud formation. Other possible culprits may be the increase of methane or water vapor, both of which can generate prime conditions for the odd clouds to form.

Wednesday's successful launch marked the 50^th space shot for NASA's Launch Services Program, which oversees spaceflights that lift off atop expendable rockets.

It also marked the 38^th flight of Orbital Sciences' Pegasus rocket since the booster made its spaceflight debut in 1990. The rocket carried the emblem of Virginia Tech university, where AIM deputy principal investigator Scott Bailey is an assistant professor, to honor the memories those killed by a student gunman at the school last week.

AIM is also NASA's first space mission ever to be governed by a historically black college, Russell said.

"It's a very big thing for us," he added.

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