For shuttles, a packed schedule lies ahead

Endeavor's liftoff, set for late Wednesday, marks an accelerated pace of launches for NASA.

Wednesday evening's launch of the space shuttle Endeavor marks the onset of a tightly packed set of launches over the next nine months, as NASA pushes to complete the International Space Station and retire the orbiters by 2010.

Barring the unforeseen, a shuttle is slated to leave the launch pad every other month through April. It's an ambitious schedule for the National Aeronautics and Space Administration, which has completed only five missions over the past two years, since resuming flights after the 2003 Columbia tragedy.

Still, the schedule seems tame by pre-Challenger and pre-Columbia standards. After the Challenger disaster in 1986, the National Research Council estimated that NASA could loft 11 to 13 flights a year with a four-orbiter fleet. Three orbiters – the number remaining after Columbia went down – could handle six to eight flights a year.

With five missions between August and the end of April, the shuttle program, like a marathon runner who sees the finish line, is beginning its "kick" to the yellow tape.

"A lot of people said, 'Boy, that's quick,' " said Kim Doering, deputy manager of the space shuttle program during a preflight briefing last month, noting that at the time two orbiters were in the program's processing facility and Endeavor was headed to the pad. Agency officials acknowledge that preparing the shuttles for their missions has been a stretch for workers at the Kennedy Space Center. "But when you look at the rest of the assembly sequence, this is the pace we'll be on," says Ms. Doering.

The seven-member crew for this mission includes Barbara Morgan, a former elementary school teacher who was Christa McAuliffe's backup for the Challenger mission (see story). Then, President Ronald Reagan had outlined a goal of sending private citizens into space aboard the shuttle, beginning with a teacher. After the Challenger disaster, the program was canceled.

In the late 1990s, Sen. John Glenn, a former astronaut, was given a seat. This helped spark a debate about who, outside the usual cast of astronauts, should be allowed aboard shuttle flights. In January 1998, Ms. Morgan became the first member of a new category of educator astronauts. In 2004, three more teachers joined her.

Whereas Ms. McAuliffe's on-orbit classroom was to be the public face of the Challenger mission, Morgan's on-orbit education efforts will be more modest. She's a fully trained crew member with assignments to fulfill aboard both the shuttle and the International Space Station (ISS).

More space-station installations

Over the next 11 to 14 days, Endeavor's crew aims to install another truss segment to the ISS and an outside storage locker for spare parts. The truss segment will bear the station's final set of solar panels, slated to arrive next year. The crew also is set to put new shuttle hardware through its paces that will allow visiting orbiters to draw electricity from the space station, rather than from the orbiters' fuel cells. This gives mission managers the option to extend an orbiter's stay for as many as three days for reasons other than emergencies or temporary technical glitches.

"Adding six to seven crew members for those extra few days allows us to do a tremendous amount of work ... to maximize the remaining shuttle flights," says Doering. This capability becomes more valuable when the shuttle Atlantis is retired from the fleet next year and, if need be, cannibalized for spare parts.

A tune-up for Endeavor

For its part, Endeavor has just come out of a major overhaul that sounds like something out of "Car Talk": new electrical wiring, new filters, new seals, two new windows, and a spiffy new GPS system to use for reentry and landing. In addition, key portions of Endeavor's thermal protection system have been upgraded, as have impact sensors on the wings' leading edges.

Wednesday's launch date represents a one-day delay imposed last week as technicians hunted down a leak they discovered during a pressure check in the cabin. They traced the problem to a small piece of debris in a pressure-relief valve just behind the shuttle's toilet. As if to underscore Atlantis's future role, technicians replaced the valve – which has since been cleaned, tested, and declared fit to fly – with one from Atlantis.

The ambitious flight schedule poses one major challenge to NASA managers, Mr. Hale acknowledges: ensuring that the workforce remains intact and motivated even as the shuttle program winds down.

From a hardware standpoint, "all signs are that we can carry on" even if the program "encounters a few little hiccups." But retaining the program's skilled workforce is "the No. 1 thing on our minds," he says.