Secret payload for the National Reconnaissance Office. The intended orbit was thought to be a "Molniya" elliptical 12-hour orbit with an inclination of 63 degrees. American data relay and signals intelligence satellites have used this orbit in the past, notably the Jumpseat series of 1971-1983. A secondary payload was later confirmed to be the first SBIRS-HEO (Space-based Infrared System) sensor. SBIRS was the successor to the DSP (Defence Support Program), which provided early warning of missile launches. Also carried the NASA/Los Alamos TWINS-A magnetospheric research payload