A spacecraft that will explore one of the last frontiers in Earth's atmosphere is nearing launch. NASA's TIMED spacecraft--named for thermosphere, ionosphere, mesosphere, energetics and dynamics--was shipped May 30 from the Applied Physics Laboratory in Laurel, Md., where it was designed and built, to Vandenberg Air Force Base, Calif.

The spacecraft is currently scheduled to launch from Vandenberg's Western Range on Aug. 10.

The two-year TIMED mission will study the effects of the sun and human-induced activities on the least explored and understood portion of Earth's atmosphere, known as the mesosphere and lower thermosphere/ ionosphere, or MLTI, which is a gateway between Earth's environment and space.

TIMED will focus on a portion of this atmospheric region located approximately 40 to 110 miles above Earth's surface, studying its basic structure and how energy is transferred into and out of this area.

"Compared to other layers of our atmosphere, we know very little about this region, which is located just a few miles above our heads," says Sam Yee, TIMED project scientist from APL, who is leading the science team's efforts throughout the mission. "A comprehensive global study of the MLTI as an integrated system has never before been accomplished." The region is too high for balloons, and rockets can only provide a brief snapshot of the area's activity near the rocket, according to Yee. Ground-based instruments can observe only a small portion of the upper atmosphere located over an observation site.

Employing advances in remote-sensing technology, the TIMED spacecraft will be the first to conduct a global study of the MLTI and will establish a baseline against which future studies of changes within this area can be compared and analyzed. "TIMED's instrument suite will work with a worldwide network of ground-based observation sites to obtain an unprecedented set of comprehensive global measurements of the region's temperature, pressure, wind and chemical composition, along with its energy inputs and outputs," Yee says.

"This mission will help scientists gain a better understanding of the MLTI region's structure and how it varies, which will help the space science community predict its effects on communications, satellite tracking, spacecraft lifetimes and on spacecraft reentering Earth's atmosphere," Yee continues.

TIMED is the initial mission in NASA's Solar Terrestrial Probes Program, part of the agency's initiative to lower mission costs and provide more frequent access to space to systematically study the sun-Earth system.

The TIMED mission is sponsored by NASA's Office of Space Science, in Washington, D.C., and managed by NASA's Goddard Space Flight Center, Greenbelt, Md. APL designed, built and will operate the spacecraft and lead the project's science effort during the mission.

For more about TIMED--including images of the spacecraft on its journey to Vandenberg Air Force Base--go to the mission Web site at www.timed.jhuapl.edu.