POSTPONEMENT of the Hubble Space Telescope launch from December to late winter or early spring is turning out to be a blessing for that much-delayed project. It keeps the $1.4-billion instrument out of harm's way as the current unusually strong sunspot cycle reaches peak activity. Would that we could say the same for two other major satellites that once were the National Aeronautics and Space Administration's pride and joy!
NASA has abandoned the Solar Maximum Mission satellite that astronauts repaired so dramatically in 1984. Increasing atmospheric drag, which is the result of solar activity that heats and expands the outer atmosphere, dooms Solar Max to a fiery re-entry later this year. Solar astronomers find it ironic that the satellite designed to study solar activity should be its victim just as that action becomes interesting. But NASA couldn't find room in its shuttle schedule or budget for a mission to boost Solar Max to a safe orbit.
To put this in perspective, Solar Max has outlived its original mission. It has observed the sun over a complete activity cycle. To continue observing now would be a bonus. But it is the kind of bonus NASA touted at the time of the Solar Max repair mission. The ability to extend the usefulness - and, hence, the cost effectiveness - of a major satellite through on-orbit repair has been one of the justifications for the space shuttle.
The space agency will try to retrieve the Long Duration Exposure Facility (LDEF). The facility is essentially an orbiting cylindrical structure that can accommodate 86 self-contained experiment trays on its outer surface.
When astronauts deployed LDEF April 7, 1984, NASA said it offered a cheap way to study the effects of the space environment on materials. Instead, LDEF became a monumental frustration to all involved. There is a variety of materials in the 57 experiments on this LDEF. They include such biological samples as 12 million tomato seeds. Astronauts were to bring all this back for study after a year in space. But shuttle schedule slippage delayed that plan. Then the Challenger accident put it off altogether.
By now, the biological experiments probably are largely - if not totally - ruined. Other materials, such as electronic semiconductors, will show the effects of a longer-than-planned space exposure. That information is likely to be useful - if NASA can retrieve LDEF. NASA plans to send the shuttle Columbia after LDEF in December. There's about a month's leeway for the recovery. After that, LDEF's orbit will decay to the point where the satellite will soon re-enter the atmosphere.
In any event, there's little talk now about a new opportunity for cheap experiments. Here is yet another lesson of the folly of overly optimistic planning for shuttle-dependent activities.
LDEF's usefulness depended on timely recovery. Solar Max and, more importantly, the Hubble Space Telescope are forerunners of expensive satellites designed to be serviced by astronauts in ways that extend their life. This includes reboosting satellites as their orbits decay. The planned reliance on timely shuttle service has not taken adequate account of unexpected shuttle schedule slippages or of the possible need for emergency reboost missions when the sun acts up more strongly than expected.
NASA should rethink its planning for astronaut-serviced satellites to ensure it can meet such contingencies.