Much of shuttle's mission success depends on behind scenes work

After the space shuttle lands here at the Kennedy Space Center, the camera crews pack up, the news people head off for other stories, the crowds disappear. Then the real work begins. It starts when the shuttle is towed to an inconspicuous beige hangar and doesn't end until the orbiter is once again on launch pad 39A.

The turnaround process is known as ``shuttle flow,'' the procedure by which the world's first and only reusable spacecraft is prepared for its next flight. The speed and reliability with which shuttle flow are accomplished may be one of the least glamorous, yet most critical, factors in determining the shuttle's ultimate success.

They may also be among the trickiest. The orbiter has over 12,000 systems to be checked and even with great care glitches in the system somehow get through. It is this unpleasant reality that has caused the shuttle schedule to be rewritten so many times and fostered doubts about its reliability among potential customers in industry and in other federal agencies.

``There's the expectation that everything NASA does is going to work perfectly,'' says Charles R. Gunn, director of operations for the shuttle program, ``but there is a learning curve that we're on until we get to that point.''

It has, however, taken longer to traverse that curve than initially predicted.

NASA had planned to complete 41 shuttle flights by this time, but only 19 mission have been completed. For all the precautions, there has still been trouble. Twice on the launch pad, for example, engines of the shuttle Discovery were shut down seconds before liftoff because of a faulty hydraulic valve in the fuel system. Most recently, a shadow was cast over the start of the Challenger mission when faulty sensors shut down one of the orbiter's three main engines after six minutes of flight.

The problems with the hydraulic system and the engine sensors highlight some of the challenges technicians face with maintaining the shuttle. Old workhorses of the NASA fleet, like the Saturn V Apollo rockets, were used only for one flight. ``We would launch and never recover them,'' recalls John J. (Tip) Talone, a squarely built, soft-spoken Tennessean who joined NASA at the start of the Apollo program and now oversees the ``flow'' of the Columbia and Discovery. ``Lots of times there may have been p arts that failed but we never discovered that because they all got dumped into the ocean.''

With the shuttle, technicians no longer have that luxury. Now they worry about the expected life cycle of many of these parts over several flights. The failed engine sensors of the Challenger, which had already been aboard four previous missions, present a problem that might never have surfaced in the older, one-shot rockets.

Likewise, tiny but critical turbine blades driving the hydraulic pumps have not been holding up as long as expected under the terrific shuttle engine blast. Originally, they were expected to last 55 missions. Instead, the turbines are being replaced after four or five flights.

The shuttle systems provide myriad opportunties for mishaps and overtime work for people like Mr. Talone. Brakes on the shuttle are routinely destroyed during each landing. The onboard toilets usually misbehave. And there are 50 to 100 heat-shielding tiles on the shuttle's exterior that need to be replaced after every mission.

Yet NASA officials say that they are becoming accustomed enough to the shuttle's quirks so that each flow phase will cease to be a new adventure. It took 187 days to prepare Columbia for its second flight. The last voyage of Challenger required only 50 days of preparation.

NASA officials expect to do considerably better in a few years. With a fourth shuttle, the Atlantis, set to fly in October, NASA has requested appropriations to build a stripped-down third hangar, or Orbital Processing Facility, to park an orbiter while the two existing bays are full.

They also want to build a tile manufacturing facility at the space center to speed installation of the critical heat shielding. By the end of the year, a second shuttle launch facility is slated to be finished.

By 1987, NASA officials say they expect to trim the flow period to a routine 35 days. That achievement will mark the shuttle's emergence from the status of research program to fulfillment of its promise as a full-fledged space transportation system.