GREENBELT -- Two NASA astronauts took an unscheduled 3 1/2 -hour walk in space yesterday, dramatically freeing a jammed communications antenna on the Gamma Ray Observatory and getting an early start on experiments for a planned space walk today.
"It's free, it's free, I can see it move," said mission specialist USAF Lt. Col. Jerry Ross, shaking loose the 60-inch dish of the satellite's high-gain antenna, which had stubbornly defied six deployment attempts made through electronic signals sent by ground controllers.
"Far out, good work," said Jay Apt, his companion on the first space walk by U.S. astronauts since December 1985. The emergency "extravehicular activity" was a contingency they had practiced in underwater simulations at Johnson Space Center in Houston.
The $617 million observatory -- with its antenna locked in position and its two solar panels fully charging the batteries aboard -- was successfully released from the shuttle's 50-foot robot arm at 6:36 p.m., 4 1/2 hours later than scheduled.
"Everything appears to be working well," said John Hrastar, GRO project manager at the Goddard Space Flight Center in Greenbelt, which will operate the 17-ton satellite round-the-clock during its two-to-six-year lifetime.
The second of NASA's four "Great Observatories" is the heaviest U.S. astronomy satellite ever launched by the shuttle. Scientists hope to search with unprecedented sensitivity for the invisible-from-Earth gamma rays, high-energy radiation emitted by some of the most violent events in the universe.
Deployment got off to a routine start early yesterday morning when mission specialist Linda Godwin grappled the huge satellite with the robot arm and lifted it from Atlantis' cargo bay. The accordion-like solar panels successfully unfolded from their stowed launch positions.
"Boy, this is sure a pretty sight," Dr. Apt, 41, said. "It's just a gorgeousspacecraft, with its beautiful black wings and all the white in the center and the silver on the top."
But the high-gain antenna -- essential for quickly transmitting to Earth the data GRO accumulates -- failed to pivot out from the satellite's side on its 16 1/2 -foot boom after restraining latches were released.
"We're not 100 percent sure, but we think a small piece of insulation on the outside of the boom hung up on a protrusion, perhaps a bolt head," Mr. Hrastar said. Ground controllers failed to "rock" the antenna loose through shuttle maneuvers or with the boom's drive motor.
It was time for the "Jay and Jerry Show," joked astronaut and Maryland native Marsha Ivins, the capsule communicator at Mission Control Center in Houston. The two astronauts left the air lock on Atlantis at 2:39 p.m.
Floating 280 miles above the East Indies, in full view of the shuttle's television cameras, Colonel Ross shook the antenna, and it immediately pivoted outward about five feet. The astronauts then loosened a few bolts on the boom hinge, and it locked into the proper position.
Relieved payload controllers at Goddard, which also designed and built one of the four instruments aboard GRO, expressed gratitude to the astronauts for their "great work that made it look easy."
After completing the emergency work in short order, Colonel Ross and Dr. Apt took advantage of the unexpected opportunity to perform some of the experiments testing equipment and techniques for space-station construction, originallyset for a still-planned EVA today.
They practiced moving along a hand rail mounted to the left of the cargo bay, and Colonel Ross, 43, laughed while doing exercises that resembled push-ups and somersaults as he held on to the rail.
Their five-day flight, launched on Friday morning, is scheduled to end at Edwards Air Force Base in California at 10:35 a.m. Wednesday. Other crew members are the commander, Air Force Col. Steven Nagel, 44, and pilot Kenneth Cameron, 41, a Marine lieutenant colonel.