WHEN the Shuttle Endeavour came home Saturday, it left the realm of clear-cut scientific achievement to enter the murky world of budget-cutting uncertainty.
Endeavour's 16-1/2 days in orbit not only made this the longest space shuttle flight so far, they also constituted one of the most fault-free scientific missions. The Astro-2 ultraviolet astronomical observatory Endeavour carried returned with what University of Wisconsin astronomer Arthur Code called ''a whole treasure chest of goodies.'' But despite such successes, the shuttle program now faces the unsettling challenge of radical cost-cutting.
Last week, an outside panel reviewing shuttle operations told the National Aeronautics and Space Administration (NASA) it had to redefine its shuttle management structure if it is to make the savings now demanded of the shuttle program. The restructuring should include turning over much of shuttle operations to a private contractor, the panel report says.
This comes on top of an earlier recommendation by an in-house review team that the agency cut some 20 percent of the shuttle work force -- nearly 6,000 jobs. That could shave an estimated $200 million off the shuttle program's current $3.2 billion annual budget.
The major question shuttle managers now face is how to make such deep cuts without compromising safety and efficiency. Sen. Kay Bailey Hutchison (R) of Texas made this point to NASA administrator Daniel Goldin earlier this month during a subcommittee hearing.
''Obviously, safety concerns come into the picture when we're in a budget-cutting mode,'' she said, with an eye toward the Johnson Space Center in Houston, which manages part of the shuttle program. For his part, Mr. Goldin says he believes substantial savings can be made without compromising safety.
The new report reinforces his view. The operations review panel includes a team of aerospace executives under the chairmanship of Christopher Kraft, a former director of the Johnson Space Center. Dr. Kraft said ''We commend'' shuttle managers for achieving ''about a 25 percent reduction in their operations costs over the past three years.'' That trimmed the program's annual budget by about a billion dollars.
But to squeeze out more costs, NASA must streamline shuttle operations radically.
Kraft said the panel believes this can be done ''with no impact to the safe and successful operation of the shuttle system.'' He noted that ''the shuttle is a very mature space vehicle'' -- about as safe as present technology can make it. Many safety measures introduced after the Challenger accident in 1986 -- such as multiple checks on work -- now are needlessly redundant, the panel concluded.
''We are doing a lot of things that don't make sense,'' Goldin said in a congressional hearing.
Meanwhile, the Astro-2 scientific teams are getting down to studying that ''treasure chest'' of data. It represents views of a wide variety of astronomical objects -- from planets to distant galaxies -- as seen in ultraviolet light. Among other things, it may reveal helium left over from the universe's birth. ''I can tell you that we succeeded in getting data needed'' to do that, said Arthur Davidsen of Johns Hopkins University in Baltimore.