Tacsat - Credit: USAF. 20,631 bytes. 167 x 341 pixels.

As part of an Air Force program aimed at eventual development of a military tactical communications system to complement the IDCSP system now in operation, Hughes built the largest experimental comsat ever constructed. TACSAT was designed to experimentally test and develop tactical communications concepts for all US military services. The mission evaluated the feasibility of using satellite communication repeaters with small surface terminal communication equipment for highly mobile land, sea and air forces. The project was led by the USAF Space and Missile Systems Organisation (SAMSO). The satellite featured a then-unique antenna array extending from the top of the drum-shaped spacecraft. The 5-element antenna array consisted of UHF antennas, each nearly 2.5 m long. Beneath them were 2 microwave horns. At the extreme top was a biconical horn used for telemetry and command. The satellite was spin-stabilised, with the solar panels rotating while the antennas and inner structure remain in a fixed position. Technology and concepts originating in this satellite would later make Hughes the leader in commercial communications satellites. Spacecraft: Cylindrical shaped aluminum structure with passive thermal control. Spin stabilised (54 rpm) to 0.1 deg using new gyrostat technique. Body mounted solar cells generated 980 W max. Three NiCd batteries with 6 AHr each. Payload: The vehicle carried two transponders, one at X-band and one at UHF. The X-band transponder had a bandwidth of 10 Mhz and a maximum RF power of 30 watts. The UHF transponder had a bandwidth of 10 Mhz and a maximum RF output of 230 watts. Provision was made for cross strapping the UHF and X-band up and downlinks with a reduced usable bandwidth of 425 kHz. Earth coverage horn antennas were used at X-band, bifilar helices were used at UHF.

Design Life: 46 months. Total Length: 3.4 m. Maximum Diameter: 3.0 m. Total Mass: 730 kg.

Experimental commsat. Space craft engaged in investigation of spaceflight techniques and technology (US Cat A).

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