Gamma-Ray Space Scope Sees Deep Into Universe

MOVE over Hubble Space Telescope, here comes your new partner: GRO. The $557 million, 35,000-pound Gamma Ray Observatory (GRO) that the space shuttle Atlantis has carried into a 286-mile-high orbit is the second of four so-called Great Observatories that the National Aeronautics and Space Administration (NASA) expects to place in orbit in this decade. It is designed to complement Hubble's powerful optical capability with an ability to observe the cosmos by the "light" of gamma rays - the most energetic electromagnetic radiation the universe produces.

Atlantis pilot Kenneth Cameron had this in mind when he told a group of schoolchildren via radio, "If we had to boil our mission down to one goal, that goal would be to continue to explore our universe 201> [by deploying an observatory] which will look outward to things that helped create and shape the beginning of the universe."

Six-hour spacewalk

Members of the Atlantis crew were to take a second spacewalk of six hours Monday after going outside Sunday and shaking loose the stuck antenna arm of the observatory. After the repair, the satellite was sent on to its two-year mission.

The observatory functioned well as it drifted away from the shuttle, NASA said. After a series of tests, it should begin sending information back in 39 days.

NASA's Great Observatory program is planned to enable astronomers to study the universe over a wide range of the electromagnetic spectrum, free of distortions and blocking caused by the atmosphere. Satellites are to be orbited later in the decade to observe infrared radiation and X-rays.

GRO is an especially important unit because cosmic gamma rays can't make it through the atmosphere. The only way astronomers have been able to study them at all has been with instruments carried by rockets and high-flying balloons and by satellites of limited capability. GRO is designed to observe a wide spectrum of gamma rays for a period of several years.

With five tons more mass than the Hubble telescope, GRO is the most massive scientific satellite ever orbited. It also is the first such satellite with a refueling capability. Although NASA has no current plan to do so, astronauts could top up the fuel tanks for GRO's maneuvering and attitude-control thrusters if needed. For the first 15 months of its work GRO is to make a full survey of the sky as revealed by gamma rays. It will then look at specific objects for the balance of its nominal two-year miss ion. But the satellite is designed for at least eight years of active service.

There is much for GRO to see. Gamma rays come from some of the most violent events in the universe. Electrons and other charged particles produce them when accelerated by powerful gravitational and magnetic forces. Such forces exist in solar flares. They are characteristic of black holes, which are objects that have collapsed to such a density that not even light can escape their gravitational fields.

Such forces are also involved in violent action seen at the cores of many galaxies, including our own Milky Way. And some gamma radiation may be left over from events that happened early in the evolution of the universe.

Vulnerability evident

But while GRO will give astronomers a welcome ability to study such events, its launch at this time also points up the vulnerability of a program such as the Great Observatories to the uncertainties of depending on shuttle transportation. GRO's launch has been postponed several times, with delays last year being due to the search for elusive fuel leaks in the shuttle fleet.

April 12 is the 10th anniversary of the first shuttle flight. That two-day mission for the shuttle Columbia opened a new era of reusable space ships. But instead of building to a launch rate of several dozen a year as orginally promised, the shuttle program has launched only 39 missions in an entire decade.

In spite of that record, NASA was, as recently as February, planning for 26 shuttle missions over the next three years. There were to be seven launches this year - including three postponed from last year - eight in 1992, and 11 in 1993. But one launch was already delayed this year when Discovery was taken off the pad in March after technicians found cracks in the hinges of flapper doors that must close to seal the orbiter's belly when the external fuel tank drops off during launch.

Such cracks have appeared in flapper door hinges on all four orbiters - including the new orbiter Endeavor, which is still in the factory. However, the cracks on Atlantis hinges are much smaller than on Discovery and Columbia hinges, and they did not delay the current mission.

NASA manned-spaceflight officials, including Administrator Richard Truly, continue to praise the shuttle as a remarkably capable spacecraft. Critics acknowledge that capability. But they point out that the shuttle transportation system overall is not robust when it comes to meeting expected launch schedules.

The NASA review committee chaired by Martin Marietta chief executive officer Norman Augustine stressed this point last fall.