The Johns Hopkins Gazette: December 3, 2001
December 3, 2001
VOL. 31, NO. 13


APL-built Spacecraft to Explore Atmospheric Frontier

Johns Hopkins Gazette Online Edition

A spacecraft destined to explore one of the last frontiers in Earth's atmosphere is scheduled to launch at 7:07 a.m. Pacific time on Friday, Dec. 7, aboard a Delta II rocket from Vandenberg Air Force Base, Calif.

Built and operated for NASA by the Applied Physics Laboratory, the two-year TIMED mission will study the influences of the sun and humans on the least explored and understood portion of Earth's atmosphere--the mesosphere and lower thermosphere/ionosphere, or MLTI, a gateway between Earth's environment and space.

TIMED (for thermosphere, ionosphere, mesosphere, energetics and dynamics) will focus on a portion of this atmospheric region located approximately 40 to 110 miles above the 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. The region is too high for balloons, he says, and rockets can provide only a brief snapshot of the area's activity near the rocket. Ground-based instruments can observe only a small portion of the upper atmosphere located over an observation site.

But through advances in remote-sensing technology, this mission will be the first to conduct a global study of the MLTI and will establish a baseline for future studies of this area. "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, chemical composition and energy inputs and outputs," Yee says.

As society has become increasingly dependent on satellite technology and communications, through devices such as cell phones and pagers, it's vital to understand the ever-changing nature of this region.

"It's important that we learn more about the dynamics of this atmospheric region because the sun's energy often has profound effects on the areas directly above and below this area," Yee says. "TIMED will help scientists develop better predictive models of space weather's effects on communications, satellite tracking, spacecraft lifetimes and degradation of spacecraft materials."

TIMED's unique interdisciplinary approach allows each of the four instruments and their experiments to be controlled independently from payload operations centers located across the country. Each of these four centers will send commands daily to the mission operations center, located at APL, where instructions for the instruments and spacecraft will be uplinked to the spacecraft once a day.

GUVI (global ultraviolet imager), a collaborative effort between APL and the Aerospace Corp. in El Segundo, Calif., is a spatial-scanning, far-ultraviolet spectrograph that will globally measure the composition and temperature profiles of the MLTI region, as well as its auroral energy inputs. APL will maintain the instrument's payload operations center from its campus in Laurel, Md.

SABER (sounding of the atmosphere using broadband emission radiometry) is a multichannel infrared radiometer designed to measure heat emitted by the atmosphere over a broad altitude and spectral range. SABER also will measure global temperature profiles and sources of atmospheric cooling such as the "air glow," which occurs when energy is radiated back into space. Hampton (Va.) University is leading SABER's science team from the instrument's payload operations center at NASA Langley Research Center, also located in Hampton. Utah State University built the instrument for NASA Langley Research Center.

SEE (solar extreme ultraviolet experiment) is a spectrometer and a suite of photometers designed to measure solar ultraviolet radiation, the primary energy deposited into the MLTI atmospheric region, which includes solar soft X-rays and extreme-ultraviolet and far-ultraviolet radiation. SEE was built by the University of Colorado in Boulder, where the instrument's payload operations center is also located.

TIDI (TIMED doppler interferometer) will globally measure the wind and temperature profiles of the MLTI region. TIDI was built by the University of Michigan in Ann Arbor, where the payload operations center is also located.

TIMED is the initial mission in NASA's Solar Terrestrial Probes Program, part of NASA'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 the NASA Goddard Space Flight Center's Solar Terrestrial Probes Program Office, Greenbelt, Md. APL designed, built and will operate the spacecraft and lead the project's science effort during the mission.

For more information about the TIMED mission, visit