Shuttle's mixed bag holds spectacular successes, serious failures
Although disappointed by a series of major mishaps, United States space officials by no means consider the mission of space shuttle Challenger a total failure.
Successful testing of the jet-powered backpacks has been an important step forward in giving astronauts a new ability to work as individuals in space. Also , rehearsal of a number of tasks that will be involved in satellite retrieval and repair has prepared the way for the Solar Maximum Mission satellite rescue operation now scheduled for April.
At this writing Thursday, mission specialists Bruce McCandless II and Robert L. Stewart were finishing their second extravehicular activity (EVA). They had once again tested the manned maneuvering units (MMUs), as the backpacks are called. They had practiced docking with the shuttle pallet satellite (SPAS) as a surrogate for the Solar Max satellite. And they had run through a simulated satellite refueling using a mockup of the fuel system of the malfunctioning Landsat D satellite.
All told, they and the other shuttle astronauts have gained much important experience, which was one of the main objectives of this 41-B mission. Nevertheless, National Aeronautics and Space Administration (NASA) officials freely admit their disappointment at the failure of the mission's main purpose - to deliver the Westar VI and Palaba-B2 communications satellites into orbit.
Failure of the payload assist module (PAM) booster rockets attached to these satellites has threatened the shuttle's important commercial role as a deliverer of payloads to orbit.
The shuttle releases such satellites into a low orbit, about 160 miles high. PAM motors then boost a communications satellite to its operational orbit at a height of 22,300 miles. Although 16 PAM firings have been successful in the past , this time the motors did not burn long enough. As a result, there are two well-functioning satellites in orbits too low to allow them to act as communications relays.
An investigation team representing all interested parties has been formed. But unless and until its engineers understand what went wrong and can fix it, all PAM's have been grounded.
That effectively puts the shuttle out of the communications satellite launching business, at least temporarily. Several more such launches had been scheduled for later this year.
The mission has suffered other failures as well. But here the astronauts and ground controllers have been able to work around them.
The biggest such failure was loss of a target balloon with which the Challenger team was to practice the rendezvous maneuvers needed to retrieve the Solar Max satellite. The balloon was destroyed after it was released from the shuttle. A NASA spokesman explains that the equipment involved was a cheap ''off-the-shelf'' item. It had a 50 percent failure rate in ground tests.
So, he says, ''NASA engineers were not too surprised when it failed.'' Use of such items is a cost-saving strategy NASA now follows when safety or high-priority objectives are not involved.
The NASA spokesman says that the astronauts were able to make radar contact with a balloon fragment and to acquire it with an optical tracking device. Thus the rendezvous radar and optical alignment system has been tested as planned. The rest of the rendezvous proceedure is already well understood. Thus mission officials are satisfied that the rendezvous proceedure has been adequately tested.
Mission specialists McCandless and Stewart also were unable to practice the Solar Max docking maneuvers as fully as expected when the shuttle's mechanical arm stiffened up Thursday. It could no longer move from side to side. This meant that the SPAS could not be carried on the arm and slowly rotated as planned. The astronauts were to use the MMUs to try match their rate of revolution around the pallet with the pallet's spin - a maneuver needed with the spinning Solar Max vehicle. However, they did practice docking with the SPAS as it lay fixed within the shuttle cargo bay, as they had done on Tuesday.
There also was an EVA ''bonus.'' A foot restraint had worked loose and was drifting away from the shuttle. But, as mission commander Vance Brand maneuvered the shuttle, McCandless, tethered to the spacecraft, swiftly moved down the tether wire and grabbed the object with his feet. It was another ''space first'' for US astronauts - retrieval of equipment that might simply have drifted away forever.
Thus shuttle mission 41-B has been a mixed achievement for the US. What had seemed a growing commercial opportunity for shuttle satellite delivery has received a serious, if temporary, setback.
Just how serious and how temporary this may be could not be assessed at this writing. Yet valuable, indeed essential, testing has been carried out that opens a new dimension in astronaut operations and points the way to servicing satellites, such as the Solar Max vehicle, in orbit.