Yesterday at church, I had the odd experience of telling a couple of friends that I hope they can't make it to the men's Fellowship Christmas party. And a couple of weeks ago, I was rather pleased that one of these guys couldn't join me to watch the Texans play his favorite team because of a work-related meeting.

Now that may sound weird, but around here it isn't -- it is a sign that a launch is imminent, and that everything is going according to plan. After all, the guys who will miss the Christmas party are part of the team that will be guiding this little project once it gets of the ground on Thursday night.

They wield no scalpels, but seven U.S. and European shuttle astronauts will be prepared to carry out electronic bypass surgery when they lift off this week to overhaul an outdated power system aboard the international space station.

Many involved in Discovery's upcoming 12-day flight consider it among the most challenging of the 33 space station construction missions that will be flown by NASA shuttle crews.

"This is a major milestone in space station assembly," said NASA's John Curry, the mission's lead space station flight director. "I will be pleasantly surprised if everything works without a hitch."

Curry's planning team has spent more than four years preparing a timeline of critical procedures that must be carried out by the astronauts, in concert with activities in Mission Control.

If successful, the shuttle crew will replace the station's 6-year-old temporary power system with a permanent electrical grid.

The overhaul will provide electricity to power European and Japanese science modules when they are added to the station in late 2007 and 2008. The work also will enable the 220-mile-high orbital outpost to house six full-time astronauts in three years, twice the current population.

Mission Control will interrupt the flow of electricity to half of the space station during two of the shuttle crew's three spacewalks. The interruptions will enable the spacewalkers to make more than 150 changes to external power lines.

"It's just like it was in your own home when your mother told you to turn off the lamp before you unplugged it," said astronaut Robert Curbeam, who will lead each of the near seven-hour outings.

Equally as worrisome, one of two 120-foot-long solar panels that have supplied electrical power to the station for the past six years must be retracted. The never-before-attempted retraction is necessary to provide clearance for a pair of similar panels on the solar power module installed on the station by the Atlantis astronauts in September.

Stretching 240 feet, the panels on the new power module are designed to rotate like a slow-turning aircraft propeller to collect sunlight that can be converted into electricity.

To establish the new electrical grid, the shuttle crew and flight controllers also must activate four external power distribution boxes and a pair of coolant pumps that have been dormant since they were installed four years ago.

The challenge for the shuttle crew and ground controllers will be to activate the pumps as quickly as possible after the distribution boxes are switched on during the second and third spacewalks. The cooling fluid circulated by the pumps prevents the boxes from overheating.

Discovery's launch from NASA's Kennedy Space Center in Florida is scheduled for Thursday at 8:36 p.m. CST.

The liftoff will be the first at night in four years. According to shuttle managers, NASA must resume nighttime launches if the agency is to finish assembling the half-built station. The project must be finished by 2010, the White House-imposed retirement date for the space shuttles.

"At this stage, every mission is critical. Every mission depends upon the success of its predecessor," said Mark Polansky, Discovery's commander. "Every mission that follows is concerned with how we finish."

Discovery's mission was once scheduled to lift off in July 2003, six months after the shuttle Columbia's in-flight destruction. In September, the Atlantis astronauts carried out the first of 15 flights needed to finish the space station.

After the cause of Columbia's breakup was traced to damage from foam insulation loss during liftoff, NASA used daytime launches for the best use of cameras that would track any loss of foam from the shuttle's external fuel tank. With no debris causing serious damage, NASA is more confident about night launches.

Discovery's crew will deliver an 11-foot-long addition to the station's solar power network.

Once the astronauts reach the orbital base, they plan to hoist the 4,100-pound aluminum truss segment from the shuttle's cargo bay with a robotic arm.

During the mission's first spacewalk, Curbeam and European Space Agency astronaut Christer Fuglesang plan to bolt the $11 million extension to the station. If the older solar panel refuses to retract, Curbeam and Fuglesang would be directed to use battery-operated ratchets to reel in the panel.

The spacewalkers could also face problems as Mission Control attempts to activate the dormant power distribution boxes and coolant pumps on the second and third outings.

Managers could add a fourth spacewalk. Replacement boxes and pumps are already positioned aboard the station.

"You are basically re-wiring your house while you live in it," said Kirk Shireman, who chairs NASA's space station mission management team. "So, we have spent a lot of time over the years developing procedures to back out of our procedures, another reason why this fight is so complicated."

So guys, we'll all be thinking about you when the gift exchange is going on -- because we know that you have something much more important to do. Good luck and Godspeed to all involved in the Discovery launch and mission.

Posted by: Greg at 11:49 PM | No Comments | Add Comment
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