Space Shuttle Discovery Meets Rocket Boosters for Final Mission

This story was updated at 4:55 p.m. ET.

NASA attached the space shuttle Discovery to its fuel tank and twin rocket boosters over the weekend to gear up for the spacecraft's final voyage to orbit later this year.

Discovery was firmly attached its 15-story external fuel tank and solid rocket boosters Saturday after a slight delay due to a loose attachment nut that slipped into the spacecraft's aft compartment on Friday. The 100-ton shuttle was hanging vertically near its external tank inside NASA's cavernous Vehicle Assembly Building at the Kennedy Space Center in Florida when the nut slipped loose.

Shuttle technicians were able to retrieve the nut by setting up access gantries to reach a door in Discovery's aft compartment ? something not usually done with a shuttle hanging in its vertical launch position.

NASA plans to begin rolling Discovery out to its seaside launch pad on Monday, Sept. 20 at about 8 p.m. EDT (0000 Sept. 21 GMT). Officials at the Kennedy Space Center are expecting hundreds of space center workers to turn out to watch the event. The shuttle moved from its hangar to the Vehicle Assembly Building on Sept. 9.

"We're allowing a number of employees to bring their families out to see the rollout," NASA spokeswoman Candrea Thomas told SPACE.com. "I expect we'll see several hundred."

Discovery is slated to launch Nov. 1 on an 11-day mission to the International Space Station that will mark the spacecraft's final trip to space. The mission, STS-133, will be Discovery's 39th spaceflight and is expected to deliver a storage room to the International Space Station along with a humanoid robot assistant for the outpost's astronaut crew.

NASA plans to retire its three remaining space shuttles ? Discovery, Atlantis and Endeavour ? next year to make way for a new plan aimed at sending astronauts to visit an asteroid by 2025. Discovery is the oldest of NASA's space shuttle fleet.

Only two more shuttle missions are currently scheduled, including Discovery's November flight, before the reusable space plane fleet is retired. The shuttle Endeavour is slated to fly the final shuttle mission in February 2011. There is also discussion in Congress on the possible addition of one extra mission to be flown by Atlantis sometime next year.

• Gallery - Shuttle Discovery's Midnight Launch
• Graphic: Inside and Out ? the International Space Station
• Final Countdown: A Guide to NASA's Last Space Shuttle Missions

This story was corrected to reflect that Discovery's last mission will be STS-133 in NASA's shuttle manifest.