Jumpseat 1, 2, 3, 4, 5, 6, 7, 8

Jumpseat 1 [NRO]

Jumpseat signal intelligence satellites were launched by Titan-3(33)B Agena-D or Titan-3(34)B Agena-D into highly elliptic Molniya-type orbits. These orbits were very similar to those of Quasar (SDS) classified communications/data relay satellites, and identification of a launch in either series as Quasar (SDS) or Jumpseat may differ from analyst to analyst.

The Jumpseat satellites were built by Hughes on the spin stabilized HS-318 bus, very similar to TACSAT and Intelsat-4. They featured a large partially foldable SIGINT dish antenna dish and a smaller downlink dish-antenna on a despun platform.

The primary purpose of this series was to monitor Soviet ballistic missile warning radars in the far north. In their elliptical orbits they would move very slowly over the northern hemisphere for most of their orbital period, allowing interception of the radar signals. It was reported, that these satellites operated in conjunction with P-801 satellites. Later they were also employed in general SIGINT and COMINT missions.

Another purpose was reportedly the interception of microwave line-of-sight communications beams. Since they would move slowly through the beams during their orbit, a constellation of such satellites was required to monitor Soviet communications throughout the day.

The satellites also probably integrated ELINT and other SIGINT functions and intercepted up- or down-links from Soviet Molniya strategic communications satellites. An additional infra-red early warning payload has also been reported.

The SIGINT payload operated in transponder mode, so that the intercepted signals were directly downlinked to the ground station.

The Jumpseat satellites were in use from 1971 to 2006. They were succeeded since 1994 by the larger Trumpet series.

Note: The identification of some of these satellites is not definitely confirmed. Some may be in fact Quasar (SDS) relay satellites, which used the same Titan-3(34)B Agena-D launch vehicle and the same orbits.