The US activities in military satellite communications systems began in July 1967 with the launch of three Initial Defense Communications Satellite Program (IDSCP) satellites. These satellites were designed to be launched in groups of up to eight, and a total of 26 IDSCP satellites were launched in four groups by TITAN 3C launch vehicles to near equatorial, 18,300 statute mile orbits. These satellites, each weighing about 100 pounds, drifted from West to East at a rate of up to 30 degrees per day.
Each satellite contained a single X-band transponder with a 26 Megahertz (MHz) bandwidth. These satellites supported experimental terminals used to evaluate voice, imagery, computerized digital data, and teletype channels using Frequency Division Multiplex/Frequency Modulation (FDM/FM), Differential Phase Shift Keying (DPSK), Multiple Frequency Shift Keying (MFSK), and Spread Spectrum Multiple Access (SSMA) modulation techniques. While designers planned for the satellites to last three years, the IDCSP satellites were designed for a five year year life and were to turn off after six years.
One satellite was modified to include and electronically despun
antenna platform (IDSCP4-8 called DATS). Electronically despun
antenna platforms are not in use today because the acquisition problems which were disclosed by
the experimental DATS configuration.