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NASA retires 'queen' of tracking satellite fleet
BY STEPHEN CLARK
SPACEFLIGHT NOW

Posted: October 13, 2009


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More than a quarter-century after a hard-luck launch aboard the shuttle Challenger, the pioneer of NASA's constellation of tracking and communications satellites is being retired from service.


Artist's concept of the TDRS 1 satellite. Credit: NASA
 
Named TDRS 1, the satellite's last traveling wave tube amplifier recently failed, rendering the craft unable to support most of its users' Ku-band data relay and telemetry needs, according to Roger Flaherty, the Space Network project manager at NASA's Goddard Space Flight Center in Maryland.

The failure led NASA officials to finally retire TDRS 1 after operating almost four times longer than designed. Officials can still command the satellite, but it is now useless to customers.

"We are going to relocate TDRS 1 and that relocation process will start on or about the 21st of October," Flaherty said.

TDRS 1 is currently located in a geosynchronous orbit more than 22,000 miles above Earth. At that altitude, satellites' orbits match the speed of Earth's rotation, causing spacecraft to hover over a specific geographic region.

Now positioned at 49 degrees west longitude, TDRS 1 will soon be moved to a nearby temporary slot for final decommissioning activities, according to NASA.

"We'll park it there as we put together definitive plans to what we call supersynch the spacecraft, that is to take the orbit up 300 kilometers (186 miles) from the geosynchronous arc," Flaherty said.

The higher altitude will help make room for new satellites in the crowded geosynchronous orbit.

"This is keeping with the NASA policy for debris mitigation and to be good stewards so that we don't leave derelict spacecraft on the arc," Flaherty said.

NASA has moved the TDRS 3 satellite, launched in 1988, to the 49 degrees west location from a station over the Indian Ocean to replace TDRS 1.

The 14-year-old TDRS 7 spacecraft was pressed into service over the Indian Ocean, taking the place of TDRS 3 in the satellite shuffle.

Built by TRW, now part of Northrop Grumman, TDRS 1 was launched aboard the shuttle Challenger on the STS-6 mission on April 4, 1983.

After deployment from Challenger, TDRS 1's Inertial Upper Stage booster spun out of control and stranded the satellite almost 10,000 miles short of its planned orbit.

Tumbling at up to 30 rpm, the satellite separated from the doomed rocket and engineers finally regained control to gradually guide the craft to its operational orbit using tiny on-board thrusters.

The effort took several months and burned about 800 pounds of fuel, but TDRS 1 was able to begin service by the end of 1983.

 
TDRS 1 is deployed from the shuttle Challenger in 1983. Credit: NASA
 
TDRS 1 supported an array of NASA missions, ranging from the space shuttle to unmanned probes like the Hubble Space Telescope.

Its NASA career was highlighted by recovering data from the Compton Gamma Ray Observatory after its recorders failed and being the first satellite to monitor a space shuttle deorbit burn from a perch over the Indian Ocean, according to Flaherty.

The satellite was also the first to collect and beam back live data during launches from the Kennedy Space Center in the early 1990s.

"It had an illustrious career," Flaherty said. "It saw service over the Atlantic Ocean. It was the first spacecraft that we took down to the Indian Ocean, when we put a ground station in Canberra, Australia."

After years of operations, TDRS 1's orbit naturally drifted to a higher inclination, allowing it to appear above the horizon at the poles. This provided one of the few satellite communications opportunities for researchers and explorers at high latitudes.

For the last decade, TDRS 1 has primarily been used by the National Science Foundation's Amundsen-Scott South Pole Station in Antarctica.

"It's sort of a TDRS-centric lifestyle on the South Pole with the scientists and the personnel down there using TDRS when it breaks the horizon for their S-band voice-over-IP, email messages, and talking to their loved ones at home," Flaherty said.

A Ku-band communications link was also used to transmit science data from the outpost back to the United States.

TDRS 1 famously provided a telemedicine link between a physician in Antarctica and doctors in the United States to help conduct an emergency knee surgery in 2002. The satellite was also instrumental in broadcasting the first Internet Web cast from the North Pole.

The replacement TDRS 3 satellite will pick up some of the communications support for the South Pole Station. The 31-year-old GOES 3 weather satellite, now relieved of its forecasting duties, is also used as a relay link with the South Pole, according to the National Science Foundation.

Because of its age and unstable orbit, TDRS 1 stopped supporting active NASA missions in the late 1990s.

"It has labored long and hard in obscurity because we had declared it a residual resource and some of the services that we normally provide to other customers were not available from TDRS 1. But it was a great spacecraft and we're going to miss it," Flaherty said.

Engineers were able to continuously improve TDRS 1's capabilities even though the satellite is ancient by space standards.

"They're bent-pipe repeaters is what they are. The smarts are at either end, either on the (user) satellites or the ground systems," Flaherty said.

As the first member of the Tracking and Data Relay Satellite System, or TDRSS, the spacecraft led NASA's effort to close communications gaps with orbiting space missions.

"It's the queen of our fleet," Flaherty said.

Before TDRSS, ground controllers could only contact satellites and crewed spacecraft as they passed over a scattered network of ground stations.

The satellite system increased communications coverage of NASA missions from less than 20 percent of each orbit to nearly 100 percent of the time, according to Flaherty.

Eight satellites will remain in the fleet after TDRS 1's retirement. One spacecraft was lost in the Challenger accident in 1986, and it is the only satellite in the constellation not operating today.

NASA says two operational satellites are positioned over the Atlantic, Pacific and Indian Oceans to provide global communications coverage.

Two new TDRSS craft are being developed for launch in 2012 and 2013.

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