Columbia's other crew -- instruments that probe, measure, monitor

While astronauts Jack Lousma and Gordon Fullerton claim the limelight, other participants in the space shuttle Columbia's third mission are quietly going about their business.

These are the scientific and environmental monitoring instruments mounted in Columbia's equipment bay. They are, in their own way, as essential to the test flight program as are the human crew members.

Columbia was well into its third day of this seven-day mission at this writing. In spite of loss of a number of tiles in noncritical areas and minor problems with spaceship hardware, the mission, so far, has been going well.

However, although the instruments have been busily working, it is a little early to have many results. Some preliminary readings from one instrument are encouraging. This equipment is looking for light scattering from any particles floating about Columbia. Astronomers and Earth scientists hope, on future shuttle flights, to make observations that such light scattering would impede. Scans of the Earth made so far show little scattering effect.

The instruments' payloads fall into two broad classes. Some are trying out the shuttle as a platform for scientific observations and gathering useful information in the process. In particular, solar physicists hope to ''see'' X-rays from a solar flare, should one occur. Other instruments measure environmental effects that equipment carried in the shuttle bay must withstand. Besides weightlessness and the accelerations and vibrations of launching, there are stresses of heating or cooling and possible exposure to cosmic rays and various kinds of contamination.

The shuttle orbiter equipment bay is large. It measures 15 feet in diameter by 60 feet in length. It can carry up to 65,000 pounds of payload. Sometimes the bay will be filled largely with satellites to be left in orbit. Many other times , however, it will be filled with scientific equipment such as Spacelab. Supplied by the European Space Agency, this is a laboratory where scientists and technicians can work and from which they can control external instruments such as telescopes. However, on most flights, there will also be small instrument packages tucked away here and there in the equipment bay, even though a particular mission may not be scientific in nature.

Payload experts, such as Robert Naumann of the National Aeronautics and Space Administration, emphasize the importance of learning all they can about the shuttle environment during the flight testing period.

Mr. Naumann explains, for example, that scientists are concerned about rocket exhaust gases or other particles and gases of spacecraft operation leaking into the bay and contaminating instruments. All of the shuttle test flights, including this one, carry equipment to monitor this. After the second flight last November, Naumann says the environmental engineers were pleased to find no significant contamination of the equipment bay due to the launch. Now, he says, they want to see if this cleanliness is again realized.

Some of the problems that instruments might encounter are subtle. The shuttle orbits at a height of about 150 miles. That is well within the outer fringes of Earth's atmosphere. The shuttle moves through a very thin gas of electrically charged particles. Consequently, an electric charge can build up on the shuttle's insulating tiles. This charge, in turn, could interfere with some instruments in the equipment bay. Thus Columbia carries equipment to study any charge buildup.

Scientists planning some kinds of studies are also interested in the gas of positively and negatively charged particles, called a plasma, immediately around the shuttle. The 50-foot-long mechanical arm from Canada is being used to sample this. It will weigh a plasma sniffer -- the Plasma Diagnostics Package (PDP) from the University of Iowa -- on each side of the spacecraft.

One of the most promising items aboard is an inconspicuous little cannister mounted at the rear of the equipment bay. This is the can that will carry a ''getaway special.'' This is a self-contained experiment that can look after itself. Its low cost -- $10,000 at most, with only $500 required in advance -- opens up space experimentation to a wide range of small enterprises and individuals. Over 300 reservations for ''getaway specials'' have been made.