Mysterious Flashing Satellite

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Considering that STS-28 was such a historic mission, the official announcement from NASA spokesman Brian Welch, a couple of hours after launch, was a flat, businesslike "The crew of Columbia has been given a 'go' for orbital operations.'' The primary payload was deployed at 8:06 pm, about seven-and-a-half hours into the mission; at the time, John Pike - a space policy analyst for the Federation of American Scientists - speculated that it was a massive 14,500-kg 'KH-12' satellite, one of the latest generation of 'Key Hole' photographic-reconnaissance platforms that can trace their lineage back to the 1960s.

Pike commented at the time that the KH-12 was the Pentagon's most expensive payload ever orbited, with an estimated price tag at close to a billion dollars. Other observers, including Aviation Week & Space Technology, suggested that it was a

A mysterious, 'flashing' satellite 105

somewhat-lighter Strategic Reconnaissance Satellite, known as 'SRS'. Still more civilian sources speculated that the satellite, whatever it might have been, was capable of manoeuvring itself to an orbital altitude of about 480 km, from which vantage point it could take photographs with a resolution as fine as a metre.

More recently, it has come to light that STS-28's payload was most likely a member of the second-generation Satellite Data System (SDS)-B family of US Air Force military communications satellites. Doubts over whether it was a KH-12 were raised within weeks of its launch, when ground-based observers noted that it 'flashed' - as sunlight reflected from its solar panels - at regular intervals, a phenomenon not usually consistent with a spying platform.

Certainly, it was not - unlike the huge Lacrosse radar-imaging satellite placed into orbit by Hoot Gibson's STS-27 crew in December 1988 - deployed with assistance from the RMS, which apparently was not carried on STS-28. The first photographs of what an SDS-B looked like were not actually made public until the spring of 1998, almost a full decade later, when the National Reconnaissance Office released pictures and videotapes of two military satellites. One was identified as an SDS-B, built by Hughes, and looked physically similar to the drum-shaped Intelsat-VI series of communications satellites.

The US Air Force began to develop the first-generation SDS in 1973, granting the contracts to Hughes. The satellites provided the US intelligence community with a network of Earth-orbiting relays capable of transmitting real-time data and images from spy satellites that were out-of-range of ground stations. Another of their responsibilities was to support voice-and-data communications for covert military operations. The second-generation SDS-B series - the first of which flew on STS-28 -operated in high-apogee and low-perigee Earth orbits, as close as 400 km and as far as 38,000 km, at steep inclinations, achieving apogee over the northern hemisphere.

This enabled them to cover two-thirds of the globe, relay KH-11 satellite data of the entire Soviet land mass and cover the entire north polar region in support of US Air Force B-52 aircraft communications. Such wide coverage was not available to geostationary satellites 36,000 km above the equator. The SDS-B featured two 4.5-m-wide dish antennas and a third, smaller, 2-m-diameter dish, which provided a Ku-band downlink. Overall, the satellite was 4 m long and 2.9 m wide with a launch mass that has been estimated at close to 3,000 kg.

In total, three of these cylindrical, solar-cell-covered SDS-B satellites were deployed by the Shuttle: on STS-28, STS-38 in November 1990 and STS-53 in December 1992. Although it is unclear how they were deployed, they were possibly released like the Leasats: in effect, they 'lay down' in the payload bay with their 'top' facing the crew cabin and were 'rolled out'. Alternatively, during its pre-Challenger 'commercial' days, the Shuttle was booked to carry Hughes HS-393 satellites, including members of the Intelsat-VI family, which occupied 'cradles' in the payload bay and would have been 'tilted' upwards before deployment.

In whatever manner the satellite was deployed, it is certain that Columbia performed a separation manoeuvre at 8:58 pm on 8 August. A second payload, weighing just 125 kg, was also deployed during the STS-28 mission and has been rumoured to have been some kind of 'ferret' satellite for radio and radar signals-

intelligence-gathering purposes. The remainder of the mission went well and the crew tended a number of military experiments in Columbia's middeck and two others in GAS canisters. A few minor problems were experienced with RCS thruster failures, but none was sufficient to impact the mission's objectives.

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