Canyon was the first series of near geostationary ELINT/SIGINT
satellites launched under the designation AFP-827. Reportedly they consist of a large (ca.
10 m diameter) antenna and are three axis stabilized. The purpose of the Canyon series is
to pinpoint radar locations. For that purpose they are deployed into a 24 h orbit, which
is not geostationary, so that triangulations can be made from different points. They were
succeeded by the Chalet / Vortex series. As the orbital data
reported is not quite consistent, it is unclear, if the Canyons were deployed directly
into the final orbit by the Agena-D or if they used a
apogee kick motor. Recent analysis by Jonathan McDowell hints to the first theory, with
the Agena-D remaining attached to the spacecraft
during the first three missions.