NASA Chooses The Lesser Of Three Evils

ANN REALTIME REPORTING 12.22.06 17:40 EST: After foregoing a first landing opportunity earlier this afternoon, the space shuttle Discovery touched down in a murky twilight at precisely 17:32 EST at Kennedy Space Center today ending a thirteen-day mission for STS-116 and Discovery's 33rd trip to space.

The NASA rule book says night begins at sunset plus 15 minutes, so the crew will have to log this one as a day landing.

Forecast weather at both KSC and backup landing site Edwards AFB, CA for today threatened to preclude landing at either, but a last minute improvement in Florida's weather allowed the orbiter to sneak in.

STS-116 Commander Mark Polansky fired Discovery’s jets at 16:26 EST to begin the descent to KSC.

While at the ISS, the Discovery's crew continued the construction of the space outpost adding the P5 spacer truss segment during the first of four spacewalks. During two more spacewalks astronauts rewired the station’s power system from a temporary to a permanent configuration.

Managers added a fourth spacewalk to manually retract a recalcitrant solar array that had folded improperly.

Discovery also delivered a new crew member and more than two tons of equipment and supplies to the ISS, most of which were located in the new SPACEHAB cargo module. Almost two tons of equipment no longer needed on the station returned to Earth aboard Discovery.

Discovery is set to launch again in October as part of STS-122 delivering the European Space Agency's Columbus Laboratory to the International Space Station.

ANN joins the rest of America in saluting the flight and ground crews that made this successful mission possible!

PREVIOUS REPORTS:

14:15 EST: NASA has chosen not to attempt a landing during its 15:56 EST window of opportunity at the Kennedy Space Center in Florida.

Storms in the area of KSC have made the weather situation too fluid for NASA's conservative flight controllers.

The agency's next opportunity is around 17:30 EST at either KSC, Edwards AFB, CA or White Sands, New Mexico. The current observation at EDW indicates light westerly winds, but the latest forecast for the period calls for a direct crosswind of 12 gusting to 18 knots. The shuttle has a 15 knot crosswind limit.

NASA used one of its extra mission days -- normally reserved to give the agency more landing options during times of poor weather or other unforseen circumstances -- for an additional spacewalk to manually retract a balky solar panel.

ANN will continue to update this story as it develops. Keep checking back for the latest!

09:00 EST: Although engineers and managers at NASA have operationally cleared the shuttle Discovery for a landing today, the agency is still unsure of exactly where the orbiter is to set down.

NASA's entry director Norm Knight told the Associated Press, "As we get closer, we'll have much more certainty on what we're really faced with."

A massive weather system wreaking havoc with Holiday travelers for the past few days has now moved east of the Mississippi bringing clouds, wind and rain from the gulf coast to Canada.

NASA's primary landing site is Kennedy Space Center in Florida. The orbiter has two opportunities to get into KSC, the first at 15:56 EST, the second at 17:32 EST. The National Weather Service is currently forecasting SSE winds at 17 mph with low clouds and showers. Visibility is expected to worsen into tonight.

Edwards AFB, CA is NASA's first backup landing site, but managers are concerned about the crosswinds there. The orbiter has three opportunities for landing at EDW, 17:27 EST, 19:00 EST and 20:36 EST. Forecasters there are calling for west winds at 25 gusting to 35 knots. A landing on runway 22 would make for crosswinds 50 degrees off runway heading -- the shuttle has a maximum crosswind capability of 15 knots.

NASA's last choice is White Sands, NM at 17:27 EST, or 19:02 EST. Although the weather there is forecast favorable for landing, agency managers really don't want to land there. The lack of equipment there to service the shuttle post-flight will delay its return to Florida -- up to two months NASA is saying now. That might jeopardize the Discovery's next scheduled launch in October of next year.

If NASA opts for White Sands it would be only the second time ever. The last time was in 1982 (below) and technicians complained the shuttle was contaminated by the fine sands on the runway. The powdery substance also sifted its way into the orbiter's brakes causing damage.

As for the crew, they continue landing preparations started yesterday. All flight controls check good and the final inspections of the shuttle's heat shield are complete with everything checking green so far.

"I have a lot of things to worry about on this flight that I can control, and the weather is something I can't," Discovery commander Mark Polansky told reporters from space. "I'm ready to land at any of the three sites."

NASA says it wants to get the shuttle down today or tomorrow as its fuel cells will run dry after Saturday.

Flight controllers in Houston have made their choice of landing sites clear -- apparently they all want to go home for the Holidays.

They transmitted their selection to the Discovery's crew in rewrite of the familiar Christmas song, Let It Snow:

"Oh, the weather at KSC is frightful. But at White Sands, it's so delightful. And since we have to land. Land White Sands, land White Sands, land White Sands."

Who says engineers have no sense of humor?

Keep checking back today as ANN follows the Discovery's journey home.

FMI: www.nasa.gov