Leased Satellite

David Low, meanwhile, had the task of deploying Columbia's own primary payload: a US Navy communications satellite called Leasat-5. Just as the STS-41C crew had done, the STS-32 crew would launch one satellite and pick up another. Leasat had originally been scheduled for launch on Hoot Gibson's STS-61C mission but by the time of Challenger had slipped until STS-61L in November 1986. Leasat (or 'leased satellite') was the fourth generation of Hughes-built synchronous communications satellites known as 'Syncoms'. As such, it had not one, but two names: in some quarters it was called Leasat-5 and, in others, Syncom 4-F5.

In shape, it took the form of a 2,400-kg 'drum' to provide worldwide, high-priority communications between ships, aircraft, submarines and land-based stations for the US military, as well as the Presidential Command Network. It measured 4 m tall and 4.6 m wide when 'stowed' in the Shuttle's payload bay, but after full deployment in geosynchronous orbit - when its Ultra-High Frequency (UHF) and omni-directional antennas had been swung out - its height increased to 6 m. It was a spin-stabilised satellite, covered with solar cells capable of generating 1,500 watts of electrical power.

Two helical antennas on top of the satellite provided receive-and-transmit capabilities in the 240-400-MHz UHF band, and it also carried two X-band 'horns' and the omni-directional antenna for tracking and control. The antennas were separately attached to a collapsible boom to allow them to be folded during ascent and sprung open in space; this helped to keep Leasat's costs down. When operational, the satellites provided 13 UHF communications channels, including a 500-kHz wide-band channel. They provided their own attitude-control functions, using onboard Sun and Earth sensors and thrusters, and carried nickel-cadmium batteries for backup power.

The Leasat project began in 1978, when the US Navy awarded contracts to Hughes Communications Services - today part of Boeing Satellite Systems - to build five Shuttle-deployable communications satellites, of which one would serve as a 'spare', for the Department of Defense. It was intended that Leasat would augment the US military's Fleet Satellite Communications (FLTSATCOM) network and the Hughes contract also provided for the construction of a control centre at El Segundo in California and a series of fixed and movable ground stations. The US Navy acted as the project's executive agent, working on behalf of the Department of Defense.

The 'lease' stipulated that the US military would pay to use communications channels on board the Leasats, at a cost of $84 million per year, per satellite. The first two Leasats were launched on Shuttle missions STS-41D and STS-51A in August and November 1984, followed by a third on STS-51D in April 1985. Leasat-3 suffered an electrical failure that stranded it in low orbit and was later retrieved, 'hotwired' and successfully redeployed by the STS-51I crew in August 1985. Ironically, the crew of that mission also deployed a fourth Leasat whose UHF system failed completely.

The situation at the time of STS-32's launch, therefore, was that four Leasats had been launched but only three were fully operational; and because the fourth had failed after entering geosynchronous orbit, it was too high for a repair by Shuttle astronauts. The fifth Leasat, which would be deployed by Brandenstein's crew, would thus be essential in completing the 'minimum' of four satellites needed by the Department of Defense. Its frisbee-like deployment from Columbia's payload bay was scheduled for the second day of the mission but, as with STS-61C, the Shuttle required several 'tries' before getting off the ground.

Was this article helpful?

0 0

Post a comment