'We got it!' Next task: repair Solar Max

''OK. We got it!'' Mission commander Robert Crippen's exurberant report upon capturing the Solar Max observatory evoked cheering and applause here at the Johnson Space Center.

Once again, a United States space team had turned a prospect for failure into success. Now everything is set to carry out the first repair of a satellite in space.

At this writing yesterday, the Solar Maximum Mission observatory had been securely berthed on the flight support system cradle in the shuttle cargo bay and rotated into place for repairs. The astronauts were preparing for what now was scheduled to be an intensive six-hour extravehicular activity today. Astronauts George (Pinky) Nelson and James D. van Hoften would then carry out all of the repair work that had originally been scheduled for two different sessions.

The mission is likely to be extended a day to accommodate the rescheduling. Mission planners say they are working toward deploying a repaired Solar Max tomorrow. Challenger would then return to the Kennedy Space Center Friday morning. The shuttle still would have enough supplies to remain in space for one or two days beyond Friday if weather were unfavorable for landing.

When the first attempt to retrieve Solar Max failed Sunday, mission controllers were uncertain whether they could make a second try. The rendezvous with the satellite had been perfect. The manned maneuvering unit (MMU) had delivered Pinky Nelson to Solar Max with precision. But then the trunion pin attachment device on Nelson's MMU failed to latch on to a trunion pin on the satellite in three attempts.

Nelson's efforts made the satellite spin and wobble excessively. Mission commander Crippen then brought Challenger in close so that mission specialist Terry Hart could try to grab a grapple pin on the satellite with the shuttle's arm. Because of the wobble, however, Crippen couldn't get close enough for the arm to reach the pin.

At that point, Solar Max controllers at the Goddard Space Flight Center in Greenbelt, Md., tried to reduce the satellite's spin and wobble by turning on its magnetic stabilizers. These grab on to Earth's magnetic field. But controllers were uncertain they would have the battery power to do it. They managed to get the satellite's solar panels into sunlight to recharge the batteries and gain the needed power. Thus they were able to set up Solar Max with a spin of about 0.5 degrees a second and a wobble of less than 9 degrees from the vertical - just the conditions the astronauts wanted for grabbing the satellite with the arm.

Said flight director John Cox, ''I think the gold star goes to the Goddard POCC (payload operations control center).'' Its work made the retrieval possible. Actually the shuttle team had no thought of giving up, even when the outlook was somewhat bleak. Frank Cepollina, Solar Max rescue project manager, said Sunday: ''This agency's got a lot of grip, it's got a lot of drive.''

The Solar Max repairs are as tricky as was the retrieval of the observatory in the first place. Replacing a failed attitude control systems module is a straightforward swap of a good unit for the bad one. A baffle will also be installed to protect the X-Ray Polychromator, which measures solar X-rays. That snaps in place with spring clips. It should be an easy task.

But, at first, responsible officials did not even think the replacement of the electronics box for the Coronagraph/Polarimeter - a secondary task - was possible, according to Frank Cepollina.

The special Solar Max instruments are mounted on a so-called multimission modular spacecraft system. This is a unit that contains attitude control systems , power supplies, and other facilities that any satellite would need. It is the first US space hardware designed for orbital servicing and repair. Thus its major units are packaged as replacable modules. An astronaut has to remove only two bolts to release a module.

But the upper part of the observatory was custom built for its sun-observing mission. Its various instruments were built in with no thought of orbital servicing. Thus, to replace the electronics box, an astronaut has to cut through the spacecraft's insulated shell and peel back the insulation. Then he must remove 22 subminiature screws and 14 larger ones to uncover the box, disconnect its electrical leads, and remove it. There is a specially designed power screw driver to speed the job. Reconnecting the new box will be easier since it has clips, instead of screws, for reconnecting the electrical leads.

Mr. Cepollina says one ''can do credit to (astronaut) Bruce McCandless who had the technical courage . . . to show it could be done.'' He scrounged spare parts and jumped in the tank where astronauts simulate zero gravity conditions by working under water so that bouyancy cancels their weight. There, Mr. McCandless showed that an astronaut could replace the attitude control module and repair the polarimeter. ''Until they saw McCandless doing it in the tank, the powers that be didn't think it could be done,'' Cepollina says.