At the Astrotech payload processing facility in Titusville Fla. this closeup shows part of the mated SV1 and SV2 spacecraft.

At the Astrotech payload processing facility in Titusville, Fla., this closeup shows part of the mated SV1 and SV2 spacecraft, which is being prepared for center of gravity testing, weighing and balancing. The two spacecraft are known as the Space Tracking and Surveillance System – Demonstrators, or STSS Demo, which is a space-based sensor component of a layered Ballistic Missile Defense System designed for the overall mission of detecting, tracking and discriminating ballistic missiles. STSS is capable of tracking objects after boost phase and provides trajectory information to other sensors. It will be launched by NASA for the Missile Defense Agency between 8 and 8:58 a.m. EDT Sept. 18. Approved for Public Release 09-MDA-04886 (10 SEPT 09) Photo credit: NASA/Jim Grossmann