LAST week's decision to move Discovery off its launch pad and roll it back to a maintenance facility for repair symbolizes the predicament in which Western spaceflight planners now find themselves. It upsets the National Aeronautics and Space Administration (NASA) schedule for seven shuttle missions this year. This reemphasizes the unreliability of the shuttle space-transport system. And that unreliability, along with mounting costs and lack of a clearly defined purpose, is forcing both NASA and the European Space Agency (ESA) to rethink, scale down, and stretch out their long-range manned spaceflight plans.
In short, it now looks as though what NASA calls ``the next logical step'' into space - permanent occupancy of the space-station Freedom - may not be taken until the next century.
The shuttle's immediate problem is cracks in hinges of flapper doors - two doors per orbiter - that must close automatically when the main fuel tank drops off during launch. Both Discovery and Columbia have hinge cracks. The third orbiter, Atlantis, does not. Its April mission to orbit the gamma-ray observatory satellite is unlikely to be rescheduled.
But there are no spare hinges and it will take several months to make and install new ones on Discovery and Columbia. This puts enough delay into shuttle scheduling so that one of the seven planned 1991 missions is likely to be bumped. Three of those seven missions were already bumped from last year's schedule because of time lost fixing elusive hydrogen fuel leaks.
Responding to congressional mandate and Bush administration concerns, NASA is about ready to announce yet another major space-station redesign. The original concept, which would have begun operating in 1994, has already been rethought and scaled down several times. But it still envisioned a crew of something like eight astronauts with several laboratory and living modules. ESA and Japan were to supply two of the modules. Around 28 shuttle missions would have been needed to build that orbiting dream hous e.
The new design will be simpler and will likely need only two-thirds as many shuttle missions for construction. This scaled-down Freedom station could be ready for astronaut-tended operation by around 1996, after about six shuttle construction missions. That means occupation two or three times a year for several week at a time. But permanent occupancy by four astronauts is unlikely to come until around the turn of the century.
NASA's repeated space-station redesigns confuse both Japanese and European manned spaceflight planning. ESA, in particular, is rethinking its ambitious program to build a small space shuttle, called Hermes, and an astronaut-tended orbiting laboratory of its own, as well as to participate in Freedom.
Hermes would service the free-flying laboratory satellite and be able to dock with space-station Freedom. Now Hermes's first flight may be delayed two or three years beyond its present 1998 target. The free-flying laboratory that was to be launched in 1999 may also wait several more years.
It will likely be a new millennium before Western astronauts join Soviet cosmonauts in having a permanent homestead in space. But that millennium is less than nine years away.