The first space shuttle flight of the year, scheduled to lift off Friday at 9:18 a.m., features the first U.S. spacewalk since 1985 and deployment of a $600 million astronomy satellite designed to probe the invisible universe of high-energy radiation sources.
At 35,000 pounds, the Gamma Ray Observatory is the heaviest civilian satellite ever launched by a shuttle and the second of NASA's four "great observatories" planned for this decade. The first was the Hubble Space Telescope, placed in orbit in April 1990.
"We'll get a new view of the universe, and we may very well find things no one has ever thought of," said physicist Carl Fichtel of Goddard Space Flight Center, chief scientist for one of GRO's four instruments. "It will tackle fundamental questions of astronomy today."
Those great expectations sound similar to pre-launch promises made for the $2 billion Hubble, whose flawed main mirror has limited the space telescope's vision until a repair mission can be flown in late 1993.
But John Hrastar, GRO project manager at Goddard, said the agency is confident that the science satellite -- it is not a "telescope" in traditional terms and has no mirrors -- was designed and built properly, although the traumatic Hubble experience prompted additional testing.
"We've tried to ask the general question of how GRO and Hubble were similar or dissimilar," Mr. Hrastar said. Among the areas which received added attention were the satellite's solar panels and antennas, both of which caused problems during the Hubble deployment.
The five-day mission aboard Atlantis earned NASA's leadoff spot VTC for 1991 when the launch of Discovery was postponed at least seven weeks for repair of cracks in fuel-line door hinges.
Although smaller hinge cracks were discovered in Atlantis, as well as in Columbia and the still-under-construction Endeavour, NASA officials decided Atlantis was safe to fly.
The flight, known as STS-37, will carry a crew of five: Air Force Col. Steven Nagel, 44, commander; Marine Corps Lt. Col. Kenneth Cameron, 41, pilot; and Air Force Lt. Col. Jerry Ross, 43, Dr. Linda Godwin, 38, and Dr. Jay Apt, 41, mission specialists.
On day four of the mission, Colonel Ross and Dr. Apt are set for the first spacewalk by American astronauts since late 1985, a six-hour "extravehicular activity" designed to test new equipment and techniques for possible use in building the space station Freedom.
The Gamma Ray Observatory -- 70 feet wide from tip to tip of its two solar panels -- will be deployed on flight day three into a 280-mile-high orbit high above Earth's atmosphere, which absorbs gamma rays and makes them invisible to instruments on the ground.
The rays represent "one of the most unexplored regions of the electromagnetic spectrum," said GRO project scientist Dr. Donald Kniffen at Goddard, the Greenbelt-based NASA center managing the project.
They occur at the spectrum's highest energies, with more than 10 million trillion times the energy of visible light. That energy powers them across the universe, virtually unaffected by matter between Earth and the violent celestial events that spawn them.
Since gamma rays are so energetic, they are rare -- only one or two an hour can be detected from the brightest objects -- and the observatory will point at single targets for up to two weeks at a time to collect enough data.
Scientists hope to witness the birth of elements and the deaths of stars, and gain clues into the evolution of the universe and the nature of quasars, pulsars, neutron stars and black holes -- collapsed stars so massive not even light can escape their gravity.
And they will look for answers to mysterious gamma ray bursts: random, short-lived events that can unleash more gamma-ray energy in a tenth of a second than the sun pumps out in all forms in a thousand years.
The shuttle is scheduled to land at Edwards Air Force Base in California at 9:30 a.m. EDT April 10.