Stephen Clark, over on Spaceflight Now reports that the doughty TDRS-1 communications satellite will be decomissioned and moved to a graveyard orbit this month after a legendary tour of duty. TDRS-1 was the first in a constellation of satellites that revolutionized America’s ability to communicate with spacecraft in orbit.
Prior to the TDRS constellation, staying in continuous contact with, say, the space shuttle as it orbited the Earth required a daisy-chain of ground stations circling the globe, some of which had to be installed on ships parked in various oceans. The TDRS constellation allowed high-bandwidth signals to be relayed from anywhere in orbit, greatly reducing the number of ground stations needed, and eliminating the need for ships.
Reducing the number of ground stations is not just a matter of convenience – the Chinese human space program still relies on tracking ships, so launches of the Shenzhou spacecraft have been timed to occur during seasons of the year when the seas are likely to be calmest. Russia also relied on tracking ships, until the economic collapse of the Soviet Union resulted in the fleet being scrapped, with the result that mission control could only talk to cosmonauts onboard Mir for a few minutes every orbit.
Although it was never advertised, the biggest users of the TDRS constellation weren’t NASA astronauts and scientists, but the military and the National Reconnaisance Office, who had priority use of the system for keeping in touch with their spy satellites. This occaisonally caused frustration for scientific users of the system, especially during tense geopolitical moments–in his book on the Hubble Space Telescope, The Hubble Wars, Eric Chaisson writes about the difficulty of scheduling telescope observations during the first Gulf War.
TDRS-1 had a difficult launch, and was almost a write-off when a failure in a transfer rocket engine left the satellite stranded in a elliptical orbit rather than its intended circular geosynchronous orbit. But over a period of two months, tiny thruster engines intended for attitude adjustments were used to nudge TDRS-1 into the correct orbit. In 1998, the satellite was retired from its original NASA and military communications mission and just used by the National Science Foundation to support polar researchers–notably being used to provide high-qulaity video conferencing during medical emergencies.
Now, the communications relay equipment onboard TDRS-1 has failed altogether, bringing the hardy satellite’s saga to a close. The satellite will be moved out of geosynchronous orbit later this month prior to final disposal. This typically involves sending a satellite to burn up over some uninhabited part of the Earth to prevent it from becoming a hazard to other spacecraft.
TDRS-1’s mission continues however, as the TDRS constellation has been upgraded over the years, with TDRS-10 being launched in 2002.