Soon to join the “A-train” constellation of Earth-observation spacecraft is a $424 million mission to continue measuring the solar energy reaching Earth’s atmosphere and track natural and man-made aerosols to gauge their impact on climate.

Orbital Sciences Corp. is preparing to launch the 1,158-lb. Glory spacecraft for NASA at 5:09 a.m. EST Feb. 23 on an Orbital-built Taurus XL 3110 rocket flying from launch complex 576-E at Vandenberg AFB, Calif. Orbital also built the spacecraft, using a LEOStar bus recycled from the Vegetation Canopy Lidar mission that NASA canceled in 2000.

“It is a unique satellite, and it is really two scientific missions in one,” said Bryan Fafaul, Glory project manager at Goddard Space Flight Center in Greenbelt, Md. “It contains a Sun-pointing instrument that measures solar energy, and an Earth-pointing instrument that will study the aerosols.”

Built by the University of Colorado Laboratory for Atmospheric and Space Physics, the Total Irradiance Monitor will look away from Earth to collect data on sunlight reaching the upper atmosphere, continuing a data set started 32 years ago but with much greater sensitivity and accuracy.

The Aerosol Polarimetry Sensor, supplied by Raytheon Space and Airborne Systems in El Segundo, Calif., will look down into the atmosphere, taking data in nine wavelengths from visible to short-wave infrared to track the tiny particles that either reflect or absorb sunlight, depending on their chemical compositions.

Together, the two instruments — plus others in the A-train constellation — will give scientists a much better idea of how aerosols from sources as disparate as volcanoes and chimneys affect long-term climate trends.

“We need to know their global distribution and properties with very high accuracy,” says Michael Mishchenko, the Glory project scientist at the NASA Goddard Institute for Space Studies in New York. “ … We know that the effect on climate of aerosols is comparable in magnitude to that of the greenhouse gases... .”

Data collected during the three-year baseline mission for the Glory spacecraft will be used to refine computer models of the aerosol impact on climate. The spacecraft carries enough consumables to permit at least a two-year extended mission if warranted, according to Joy Bretthauer, Glory program executive at NASA headquarters.

The scientific mission will begin after about 30 days of on-orbit checkout and verification, NASA says.