Faced with steadily increasing shuttle flight schedules, National Aeronautics and Space Administration planners are scurrying to boost orders for spare parts for their growing fleet of orbiters.
The very fact that the fleet is growing is adding urgency to the effort.
''Our initial approach was to use the production lines as kind of a spares source. And that plan is reasonably good when you have one orbiter in the field and three orbiters in production,'' says Glynn S. Lunney, manager of National STS Programs here. With three orbiters built and one in production, ''living off the production line is no longer as easy.''
Accordingly, NASA is increasing its spending for spare orbiter parts from less than $100 million last year to between $200 million and $250 million this year, Dr. Lunney says.
Though it may appear so, NASA has not waited for the well to run dry before ordering parts for Columbia, Challenger, Discovery, and, when it is delivered at the end of next year, Atlantis.
In 1981, officials began to place orders for major orbiter components, such as orbital maneuvering system engines, communications systems, fuel cells, and other big-ticket items.
But in doing so, ''We were flying blind,'' says Coye M. Jones, acting chief of the orbiter logistics office. None of the systems had been flight tested.
That fact led planners not to buy too many spares. Without flight experience, they risked stockpiling the wrong items, Lunney says.
But because of the long lead times on the major items, orders had to be placed early for pre-1987 delivery, when shuttles are scheduled for more than 20 flights.
Some of those major components include structural spares - major airframe sections for the orbiter such as wings, a midbody section, and a tail assembly.
''If you have a belly landing, or if the wing is dinged on the way up, it is much faster to have a wing ready to be put into place,'' he says.