HS-393

The Hughes 393 (sometimes referred to as the HS-393) is a communications satellite bus introduced in 1985 by Hughes Space and Communications Company. It was a spin-stabilized bus that had twice as much power as the HS-376 platform.

Design
The satellite bus was designed and manufactured by Hughes. It had a launch mass of 2.2 to 2.5 tonne, a mass of 1.35 to 1.5 tonne after reaching geostationary orbit, and an 8-year design life. When stowed for launch, its dimensions were 3.4 m in height and 3.7 m in diameter. With its solar panels fully extended its height was 10 m.

Its power system generated approximately 2,350 watts of power at beginning of life and 2,200 at end of life, thanks to two cylindrical solar panels. These panels used K7 and K4-3/4 solar cells, with more than twice the number of cells than on the HS-376. The bottom panel was retracted around the body and top panel for launch, and extended downwards for operation. It also had two 38 Ah NiH2 batteries.

Its propulsion system was composed of two R-4D liquid apogee engines with a thrust of 490 N. It also had two axial and four radial 22 N bipropellant thrusters for station-keeping and attitude control. It included enough propellant for orbit circularization and 8 years of operation.

Its payload was composed of a 2.4 m antenna that fed Ku band transponders.

Satellites
The HS-393 was a more powerful platform than the HS-376, being able to supply 2,200 kW of power versus the 1,400 kW of the HS-376HP. Only three were ever built.