One challenge after another for shuttle crew

Challenger astronauts, relieved to be in a safe and useful orbit, have settled down to one of the most demanding missions a shuttle team has yet tackled. Even with everything working perfectly, the 13 experiments packed into the spacecraft's equipment bay represented one of the most complex scientific shuttle programs yet attempted.

Now, however, after a traumatic launch in which a main engine failed, mission commander C. Gordon Fullerton and his six-member team are having to make do with a less than ideal orbit and with a reduced supply of maneuvering fuel.

Moreover, at this writing, crew members were having difficulty activating a precision Instrument Pointing System (IPS), used to direct telescopes and other sensors. The testing of the system is the single most important objective on the crew's work sheet. Supplied by the European Space Agency (ESA), the $60 million IPS accounts for the bulk of the cost of the $78 million experimental array now in orbit.

``Sorry it's taking us so long to get on the sun,'' said crew member Karl Henize, an astronomer operating the pointing system. Mr. Henize said he had made some ``rough tracks'' on the sun and a star, but was having difficulty locking firmly on the targets.

In spite of these difficulties, National Aeronautics and SHUTTLE6SHUTTLE1 Space Administration (NASA) officials are pleased that the mission has been saved. If Challenger's engine had shut down 33 seconds earlier during the launch Monday the crew would have had to abort and make an unprecedented emergency landing, probably on Crete. As it is, NASA officials are proudly emphasizing the safety and flexibility built into the shuttle hardware and its operating procedures -- a flexibility that appears to have saved a large part of this mission.

Noting this, Jesse W. Moore, NASA associate administrator for the shuttle program, explained: ``Anybody who operates in this launch business is going to have some anomalies along the way. . . . You just have to put a design philosophy in place and a system in place that can cope with certain anomalies. I think we have that in the shuttle program.''

That philosophy includes a premium on both safety and a flexibility that allows a mission to recover from mishaps as serious as the loss of a main engine. The shuttle has three such engines. These fire throughout a launch both during the firing of the two auxiliary solid rocket boosters and after they have been jettisoned. Both crew training and the programming of the onboard computers take account of the possibility of a main engine loss during launching. Thus both the crew and the shuttle system were prepared to cope with Monday's ``anomaly.''

A problem with the control system of one of the booster rockets, and with computer commands sent to handle the problem, delayed the launch. Instead of lifting off at 3:23 p.m. Eastern daylight time as planned, Challenger launched at 5 p.m. It appeared to be a perfect takeoff. Then, 31/2 minutes into the launch, a temperature sensor indicated engine overheating. Five minutes, 45 seconds into the launch, the computer shut down main engine No. 1. That's the engine at the top of the three-engine clust er.

Quickly assessing the situation, ground controllers gave the crew an OK to ``abort to orbit.'' That meant executing a well-rehearsed maneuver in which the remaining two main engines burned 86 seconds longer than the 8 minutes originally planned. A sensor in one of these remaining engines was turned off by the crew when it too indicated a high temperature. Controllers did not want the computer to shut down that engine. The crew also used the rear thrusters of the Orbital Maneuvering System (OMS) to gain added thrust and to lighten Challenger by burning off some of the OMS fuel.

All of this, plus some subsequent maneuvering, has put Challenger into a useful orbit about 196 miles high. In short, NASA's Mr. Moore said, the term ``abort to orbit'' was a misnomer. The mission did not abort. It has proceeded on its way.

At this writing, controllers and the experimenter team were replanning the mission to make the most of Challenger's position. Being some 40 miles lower than planned, the targeting, timing, and extent of some of the experiments and measurements have to be rescheduled. These include extensive study of the sun, of distant cosmic infrared sources, and of characteristics of the outer parts of the atmosphere. The schedule is also affected by the launch delay and delays introduced in coping with the engine eme rgency. Replanning must take account of the fact that there now is some 5,000 pounds (about 30 percent) less OMS fuel available than expected for maneuvering in connection with experiments.

Nevertheless, some successes have already been achieved. For example, electron beams have been shot out in a study of the high atmosphere, making a spectacular and successful display. If the difficulty can be overcome with the crucial Instrument Pointing System -- which is being tested for use on a mission in March to study Halley's comet -- much useful work may yet be done on this flight.