"In anybody's ballpark, this mission was really a home run," NASA shuttle program manager Ron Dittemore said.

A few extra innings, however, are going to be required to get shuttle Atlantis ready for a planned Jan. 18 launch with the U.S. Destiny laboratory, which will serve as the scientific heart of the station.

Atlantis had been scheduled to roll out to its seaside launch pad Monday, but the move was postponed so engineers can perform additional inspections on its twin solid rocket boosters.

The extra inspections were ordered after engineers discovered that an explosive charge designed to separate booster rockets from the shuttle's 15-story external tank failed to fire during Endeavour's Nov. 30 launch.

The so-called NASA Standard Initiator was one of two on a metal strut that connected Endeavour's left-hand booster to the shuttle's bullet-shaped fuel tank. The other fired as designed, however, and the booster separated cleanly.

Had the second charge failed, though, both the $2 billion shuttle and its astronaut crew likely would have been lost. NASA managers, consequently, want to make certain the problem doesn't crop up again on the Atlantis flight.

"We don't like going into a mission knowing that perhaps we have lost one leg of our redundancy," Dittemore said.

Engineers have traced the problem with Endeavour's booster to a damaged cable designed to route computer commands to the failed pyrotechnic charge. The damage went undetected prior to the shuttle's launch.

~

Still unclear, however, is what caused the damage. So engineers this week will attempt to pinpoint the cause and determine whether any repair work will have to be done on the shuttle Atlantis boosters.

Any repair work likely would be done inside KSC's 52-story Vehicle Assembly Building, where Atlantis now is undergoing inspections. If those inspections and any repairs take more than a week, the planned Jan. 18 Atlantis launch likely will be delayed.

"We do know that we have a full week before we start getting really tight," Dittemore said.

The planned Feb. 15 launch of shuttle Discovery with a fresh station crew, meanwhile, already is facing a delay of up to two weeks.

Onboard the shuttle when it does fly will be the so-called Expedition Two crew, which includes Russian cosmonaut Yuri Usachev and two U.S. astronauts, Susan Helms and Jim Voss.

That trio will be replacing U.S. astronaut Bill Shepherd and his two cosmonaut colleagues, Yuri Gidzenko and Sergei Krikalev, who took up residence at the outpost Nov. 2.

Their ride home, however, will be postponed to give technicians time to replace faulty jet thrusters on Discovery. NASA managers will decide later this week exactly how long the crew rotation mission will be delayed.

"It may a week. It may be two," Dittemore said. "We'll just have to see."

In either case, Shepherd and company won't be back on terra firma until early- to mid-March. The three had been scheduled to return to Earth Feb. 26 - or 118 days after their launch from Baikonur Cosmodrome in Kazakhstan.

NASA flight surgeons, meanwhile, have placed a 180-day limit on tours of duty at the international station. That's because long stays in the weightless space environment can have a harmful effect on the human muscular and skeletal systems.

Dittemore, however, was quick to note that Shepherd and his colleagues should be home well before the six-month maximum is reached.

"We know that there is about 65 days between the middle of February and the 180-day maximum that they'd like us to set as an upper limit," he said. "So we have lots of time to go up and do the crew exchange."