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updated 12/1/2010 7:47:24 AM ET 2010-12-01T12:47:24

NASA is taking a close look at the December launch options for the final flight of space shuttle Discovery as engineers continue to study fuel tank issues that have kept the spacecraft grounded for weeks.

The next launch opportunity for Discovery's final mission is no earlier than Dec. 17 at 8:51 p.m. EST (0150 Nov. 18 GMT). But, in a news conference last week, shuttle program manager John Shannon said that he would only feel confident with a mid-December flight if engineering teams had a firm understanding of what initially caused the cracks in the metal ribs on Discovery's external fuel tank.

"We'll leave the option open for a launch window for Dec. 17, but a lot of data has to come together to support that," Shannon said in the Nov. 24 briefing.

Discovery was previously scheduled to lift off on Dec. 3 from NASA's Kennedy Space Center in Cape Canaveral, Fla., but top shuttle program managers opted to delay the launch to give engineers more time to identify and assess the risks. That setback came after several other delays that thwarted launch tries in early November. [ INFOGRAPHIC: NASA's Space Shuttle from Top to Bottom ]

Top shuttle officials will meet Thursday (Dec. 2) to review Discovery's status and discuss the potential of a December launch.

Discovery's launch options

Discovery's next available window opens on Dec. 17 and runs through Dec. 20, giving NASA three possible launch attempts in four days. Mission managers are unlikely to push beyond Dec. 20, however, as the agency would want to avoid having Discovery's 11-day mission overlap with the transition into the new year.

"They've never gone over the New Year's holiday," NASA spokesman Allard Beutel told SPACE.com. "They've never done it before, and they prefer not to, but it's not something so terrible. It's not that the system would crash the computers just have to be reset."

Beutel likened the problem to the Y2K issue of 2000, but stressed that it is not actually the same thing.

The computers on NASA's space shuttles are programmed so that at the end of the year, the systems need to be reset to reflect the date as Jan. 1, instead of Dec. 32, Beutel explained. In other words, at the end of the year, the shuttle computers have to be reconfigured to change from day 365 to day 1.

"In general, to shut down and reset the computers, they need to be safely on the ground, landed or docked to the station," Beutel said. "In theory, they could do it while they're in flight, but that's never been done before."

Discovery is slated to deliver a new room and a helper robot to the space station during its final flight. The mission is NASA's second-to-last scheduled shuttle flight before the fleet is retired in 2011. An extra shuttle mission has been approved by Congress and President Obama, but final funding authorization by Congress is still pending.

Traffic jam in space

Space traffic is another consideration for Discovery's December flight options.

If Discovery is cleared to launch on Dec. 17, the shuttle and its six-astronaut crew will reach the International Space Station on Dec. 19, only two days after the arrival of three new station crewmembers also bound for the orbiting lab.

A Soyuz rocket carrying NASA astronaut Catherine Coleman, Russian cosmonaut Dmitri Kondratyev and European astronaut Paolo Nespoli is scheduled to launch from Kazakhstan's Baikonur Cosmodrome on Dec. 15.

The Soyuz TMA-20 will dock at the space station on Dec. 17, and while this could be the same day as Discovery's final launch, the two events will not conflict. After liftoff, it will take Discovery and its crew two days to enter into the station's orbit, catch up, and then dock with the orbiting outpost.

If, however, NASA is unable to launch Discovery in December and the STS-133 mission is pushed into 2011, the agency will have to establish the next launch window while balancing the space station program's already-full schedule.

"All windows are, to some degree, negotiable it's just how much you can negotiate," Beutel said. "But, that doesn't mean it's always going to be practical enough to be feasible. We have to work with the international partners and the station to change things around."

"There are a dozen and a half rockets and spacecraft heading to the station next year, so there's a lot of traffic," Beutel added. "Then there are spacewalks and work going on at the station. All that stuff has to be factored in."

What's next?

As it currently stands, NASA would be unable to launch Discovery during most of January, due to unfavorable sun angles that could cause parts of the shuttle to overheat while it is docked to the station. A couple of days may open up early in February, Beutel said, ahead of the next clear cut launch window on Feb. 27, which was originally reserved for Endeavour's final spaceflight the STS-134 mission.

If needed, Endeavour's last mission could be rescheduled for the end of April, NASA officials have said.

Still, once Discovery has been given the clearance to fly, many of the subsequent decisions on how best to carry out the mission will be guided by the requirements of the space station and its program managers.

"The shuttle program is supporting the International Space Station," Beutel said. "It's ultimately what that program and our international partners need."

You can follow SPACE.com Staff Writer Denise Chow on Twitter@denisechow.

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