NASA yesterday began nudging the $100 million Tracking Data and Relay Satellite out of the egg-shaped orbit it has maintained for more than a month and toward a circular orbit 22,335 miles above Earth, where it could be used as a communications rela w0216 ----- r a BC-05/11/83-ORBIT 05-11 0001 Space Agency Begins to Nudge Errant Satellite Into New Orbit By Thomas O'Toole Washington Post Staff Writer
NASA yesterday began nudging the $100 million Tracking Data and Relay Satellite out of the egg-shaped orbit it has maintained for more than a month and toward a circular orbit 22,335 miles above Earth, where it could be used as a communications relay station for the next 20 years.
The space agency was able to raise the perigee, or lowest point, of the satellite's orbit, by 284 miles through a complex firing of the satellite's seven small thruster engines that maintain its attitude and position in space.
That left the perigee more than 8,000 miles lower than it must be for successful communications relay, but officials said the maneuver worked so well that NASA engineers are convinced that they can repeat it often and fully correct the orbit.
The satellite was launched April 5 from the cargo bay of the space shuttle Challenger, but failed to attain its projected orbit.
"We're satisfied that we're making progress," TDRS deputy project manager Charles M. Hunter said at the Goddard Space Flight Center in Greenbelt.
"We still have a little fine-tuning to do to determine our best firing frequencies, but we do not consider that a major problem, and we're confident we can reach geosynchronous orbit," he said.
In such an orbit, the satellite would match the Earth's rotational speed to stay in the same position above Earth.
Signals to fire the TDRS engines were radioed at 12:12 a.m. EDT yesterday through the space agency's deep-space tracking antenna outside Madrid, Spain, just before the satellite reached the apogee, or highest point, of its orbit while crossing the South Atlantic near the equator north of Ascension Island.
Two of the engines were ordered to fire continuously, while the other five were to alternate their firings to maintain the satellite's stability.
After firing for 1 hour and 22 minutes, all seven engines were shut down when two of the five throttling engines began to overheat.
The goal of engineers at TRW in Redondo Beach, Calif., where the satellite was built, is to run the engines for three hours at a time.
The 82-minute duration of yesterday's firings was twice that of two test burns done last week and earlier this week.
"We're still trying to figure out the best sequence of firings," NASA spokesman Jim Elliott said at Goddard.
"We made progress today, and we are still confident we can get the satellite into the right orbit," he said.
The space agency plans to fire the engines again at 2 p.m. today, when the satellite reaches its apogee over the Solomon Islands in the South Pacific.
Some engines are fired to reposition the satellite before it begins to descend toward its perigee. Then others fire to raise it as it descends toward perigee, causing perigee to become higher.
The satellite reaches apogee approximately every 18 hours during its current orbit. Yesterday's maneuever raised the perigee 284 miles but lowered the apogee 10 miles, which did not concern space engineers, Elliott said.
The rescue effort will require at least 12 and perhaps as many as 39 more firings to bring the satellite into a circular orbit, according to officials.
The final position of the satellite is to be a spot over the Atlantic as near to the equator as possible and just off the northeast coast of Brazil.
The TDRS is the first of three identical satellites NASA hopes to use as relay stations to and from as many as 26 satellites to be launched in the next 10 years on flights of the space shuttle.
It will also be used to communicate with the shuttle.