Space agency flight directors hammered out a plan today to nudge an errant communications satellite into a higher orbit--a feat made possible only because NASA sent the satellite into space with 1,100 more pounds of fuel than necessary.
As astronauts flying the space shuttle Challenger on its maiden mission prepared to make the first shuttle space walk Thursday, flight directors in Houston discussed the series of nearly miraculous events that saved the $100 million satellite from tumbling into oblivion, or being stuck in a useless orbit.
The Tracking Relay and Data Satellite was launched from the Challenger early Tuesday with 1,300 pounds of hydrazine fuel instead of the 200 pounds it needed to stay in position above the equator for the next 10 years. NASA officials decided long ago that if it took a full tank of fuel into orbit it would not have to remove two antennas from the satellite to retain the satellite's center of gravity.
"It was kind of a non-decision, in part because nobody expected to use those antennas or to need all that fuel," one source said today at the Johnson Space Center. "It now turns out to be a very fortuitous decision because we could never have saved this flight completely if we hadn't gone with a full tank."
The satellite is now fully workable, with its two solar panels extended 57 feet from wing to wing and its pair of 16-foot-wide antennas unfurled like giant umbrellas, its 5,000 pounds ready to serve as command post for all future American Earth-to-orbit communications. Still, it remained about 400 miles below its ideal orbit.
"Our plan is to correct the total orbit of our satellite," Robert O. Aller, NASA's satellite director said today from White Sands, N.M. "We are going to adjust the total orbit geosync."
Geosync means a circular orbit 22,335 miles above the equator. There, the satellite's rotation would match that of the Earth and it would stay in the same relative place all the time. The satellite is only 400 miles below "geosync" at its high point but its orbit is irregular as a result of its engine misfiring on Tuesday. Its orbit now has a low point of 13,450 miles, almost 9,000 miles off target.
To correct that, flight directors said today they planned to burn 900 pounds of the satellite's fuel in the next week to bump the orbit low point to where it matches its high point, which is now 21,950 miles. The first in a sequence of three-hour engine burns of two of the satellite's 24 small thruster jets will be made on Thursday. The series of engine firings is expected to last six or seven days.
The astronauts seemed more engrossed with the tribulations of the satellite today than the first shuttle space walk, which two of the four-man crew will make at 4:15 p.m. EST on Thursday. Three times, the astronauts asked the Mission Control Center how the satellite they deployed in space was faring.
Challenger's space walkers on Thursday will be Story Musgrave and Donald H. Peterson. The other crew members are Commander Paul J. Weitz and Karol J. Bobko, who is serving as copilot on the flight.
If all goes well, Musgrave and Peterson will spend 3 1/2 hours in Challenger's cargo bay testing the new spacesuits they'll be wearing as well as the new tools and procedures that shuttle crews will be required to use on later flights. They will be tethered to 50-foot cables.
The suits were to be tested to pinpoint any problems in advance. On the shuttle Columbia's last flight, problems with the suits were discovered hours before the planned space walk, which was canceled.
While space agency spokesmen insisted Thursday's space walk would take place on time, Weitz called down to Mission Control late today for a private medical conference with Flight Surgeon Dr. T.E. Lefton. No explanation was given why Weitz requested the conference, but shuttle commanders have asked for them in the past when one or more of their crew fell sick. No less than half the shuttle crews have suffered space-sickness on the first five flights.
Under new NASA rules, details of such conferences are to be made public only if the mission would be affected. "This does not impact the mission," flight director Gary Coen said.
Meanwhile, the story of how flight directors were able to stop the satellite from tumbling out of control on Tuesday morning continued to unfold at the Johnson Space Center, where all shuttle flights are directed.
Dean Carpenter, the assistant project manager at TRW Inc., which built the satellite, revealed today that the satellite was so far out of control for almost three hours that it was tumbling 30 times a minute, which is almost as rapid a rate as a satellite could tolerate without being damaged.
At the same time, Carpenter said, flight directors feared that they would be unable to separate the satellite from its 2,400-pound engine in time to rid itself of all the engine's dead weight.
"We were well past the time the batteries that power the engine should have been dead," Carpenter said. "If those batteries had been dead, we would not have separated."
Flight directors saved the day by having antennas at Goldstone and Vandenberg Air Force Base in California beam continuous signals at maximum power, ordering the engine to separate from the satellite and that the satellite stop tumbling.
"I can't tell you what it felt like when we recovered the mission," Carpenter said. "It was sickening to think we could have lost the whole mission."