Rocket engineers made up lost time Saturday and top NASA officials said the shuttle Discovery was on track for blastoff Monday on a flight to deploy a $100 million communications satellite.

Astronaut Robert Crippen, chairman of NASA's mission management team, said no major problems were apparent and even the weather, which hampered work in the early hours of the countdown, appeared to be cooperating with a 90 percent chance of acceptable conditions at launch time Monday."We do not have any significant issues that we're working today so there's not a lot to report on," he said at a news conference. "The winds are predicted to be favorable. The vehicle is in good shape, we have no significant hardware issues that we're working.

"We're running a little bit behind in our countdown because of all the wind problems that we had yesterday trying to get closed out on the pad, but we have built-in holds that allow us to accommodate some of that kind of slippage. We're seeing no problems at this time for achieving a launch on Monday morning."

Discovery's launch on the 28th shuttle mission, the third since the 1986 Challenger disaster and the first of seven flights planned this year, is scheduled for 8:07 a.m. EST (6:07 a.m. MST) Monday.

At the controls will be skipper Michael Coats, 43, and co-pilot John Blaha, 46. Seated behind the two pilots on the shuttle's flight deck will be James Buchli, 43, and Robert Springer, 46, with physician-astronaut James Bagian, 37, seated alone on Discovery's lower deck.

Also on board will be four rats that had tiny holes drilled through the non-weight-bearing fibula bones in their hind legs Thursday as part of a student experiment to find out how weightlessness affects bone healing.

After the flight, the rodents will be killed so Brown University medical student Andrew Fras can study how the injuries healed in research that could shed light on how broken bones might be treated during future long-duration space flights.

Liftoff originally was planned for Feb. 18, but a series of problems, including the replacement of three high-pressure liquid oxygen turbopumps, forced NASA to delay the mission by nearly three weeks.

NASA test director Ronald Phelps said Discovery's countdown fell seven hours behind schedule early Saturday when engineers, hampered by high winds Thursday and Friday, ran into minor but pesky problems closing the shuttle's engine compartment.

But with 37 hours of contingency, or "hold" time built into the countdown, Phelps said it was a relatively simple matter to shorten an already planned eight-hour hold later in the day to make up the lost time.

"We'll reduce that hold down to one hour and basically be back on schedule," Phelps said. "This early in the count, losing those seven hours really doesn't hurt us that much. There's been a lot of hard work required, but overall, this has probably been one of the smoothest counts to date."

The primary goal of the five-day flight is the launch of a $100 million Tracking and Data Relay Satellite, TDRS, that will improve space communications while allowing NASA to shut down five ground stations scattered around the world for a savings of about $27 million per year.

Springer plans to deploy the satellite and its $45 million solid-fuel "inertial upper stage" booster from Discovery's 60-foot payload bay six hours and 12 minutes after liftoff.