Despite continuing problems with some equipment, Challenger astronauts in space and the science team on the ground are reaping a substantial harvest of data from this troubled mission. ``We have been able to assure ourselves that the science return . . . will be very high,'' says mission scientist Eugene W. Urban.
The mission team, at this writing, was still trying to recover full use of the instrument pointing system (IPS), which enables sun-observing instruments to track their targets with high precision.
Experimenters also had not been able to fix a malfunctioning instrument called SOUP. SOUP is a combination of telescope and video cameras used for studying activity of the solar magnetic field and the polarization of the sun's visible light.
Otherwise, Mission 51-F was carrying out a fast-paced research plan.
Peter Meyer of the University of Chicago says the cosmic-ray sensor has already sent back enough data to keep him and his colleague, Dietrich Muller, busy for the next two years. They are studying the composition and energy characteristics of some of the high-energy cosmic-ray particles arriving at Earth from outer space.
Several of the instruments involve studies of what physicists call plasma, a gas made up of electrically charged particles. But since there are equal numbers of positively and negatively charged particles, the gas, as a whole, is electrically neutral. Much of the matter in the universe, such as stars, is in the form of a plasma. So, too, is the thin residual atmosphere through which the shuttle travels.
One experiment, in which an electron beam is shot into this plasma environment, has already produced brilliant light displays and much useful data.
Another experiment involves the effect of water, discharged by the shuttle's orbital maneuvering system thrusters, on the high atmosphere. The electrically charged plasma particles in this part of the atmosphere -- called the ionosphere -- reflect shortwave radio signals and bounce them around Earth.
Influenced by the water, some of the positively charged particles recombine with negatively charged electrons. This process opens ``holes'' in the ionosphere, which allow the radio waves to pass through without reflection. Experimenters, who are testing the physical properties of the ionosphere, have seen several instances of this from their ground stations. They report that the holes appear to be more circular and take longer to fill in than was expected.
And, in what may be one of the most satisfying events for the shuttle team, an experiment to study the low-temperature properties of helium in zero gravity is reported to be working well. Experimenter Peter V. Mason of the NASA Jet Propulsion Laboratory in Pasadena, Calif., had thought the experiment was lost a few weeks ago. It failed before the originally scheduled July 12 launch of this mission. The delay of that launching, however, gave technicians time to refurbish the helium equipment.
Mission manager Roy C. Lester says that, in terms of the overall scientific return, recovery of that experiment helps to compensate for the loss of some data that had been expected from the other experiments and instruments in Challenger's payload bay.
For example, the moon's light has restricted some studies of distant cosmic objects, such as those being made by an infrared telescope. The moon, which would have been close to the sun two weeks ago, now is full, dominating the night sky. Also, because Challenger is in a lower orbit than planned, some observations of the sun and distant objects, which depend on precise orbital positioning, have suffered slightly.
Mr. Lester and other mission officials emphasize that the basic scientific objective is to test the Spacelab 2 pallet itself. This is a structure on which the instruments are mounted. It can be used together with the Spacelab manned laboratory, as it has on two previous flights.
Now, it is being tried on its own. Supplied by the European Space Agency (ESA), the pallet is to be used on a number of future missions. That is why giving the pallet a thorough flight test, as is now being done, is considered an important objective.
Another major objective is to flight test the ESA-supplied instrument pointing system.
If the system has any bugs, as seems to be the case, they must be discovered and corrected in time for the IPS to be used on the shuttle Astro mission to study Halley's comet next March. The Halley-observing instruments must track the comet with the kind of extreme precision made possible by the IPS. IPS should have a tracking error within one arc-second -- an error no bigger than the diameter of a quarter seen 11/2 miles away.
As of this writing, the IPS had performed some precision tracking but was not working reliably. The problem appears to be in the computer software that controls the IPS system, and the IPS ground team was working to correct it.