Space Shuttle Discovery has undergone tests to check whether repairs to its right landing gear are sound, and hopefully all that work won’t delay liftoff past an Oct. 23 target, according to NASA.

Repairs to the struts, which act as shock absorbers when the shuttle lands, were ordered after the right landing gear began to leak, involving replacement of four hydraulic seals in the landing gear.

Those repairs were a bit more complicated than one might expect. To remove the main landing gear strut and replace seals requires disconnecting and replacing the brakes and tires, disconnecting and reconnecting instruments and other requirements to allow access to the strut.

Discovery yesterday rolled over to the Vehicle Assembly Building at Kennedy Space Center, where the spacecraft is joined with its giant external fuel tank and a pair of solid rocket boosters for its upcoming STS-120 Mission to the International Space Station.

After that, rollout to Pad 39A is targeted for a week from today.

Separately, NASA managers also officially decided to add an additional spacewalk, bringing the total to an ambitious and challenging five. On the extra spacewalk, Missions Specialists Scott Parazynski and Douglas Wheelock will test tile heat shield repair techniques, extending the mission to 14 days. (Please see Space & Missile Defense Report, Monday, Sept. 17, 2007.)

Those test repairs were prompted by damage to heat shielding on prior shuttle missions, where in each case foam insulation broke off from the external fuel tank and hit the orbiter vehicle.

In the most recent shuttle flight, Space Shuttle Endeavour was hit by foam that gashed heat tiling on the underside of the orbiter vehicle, shortly after liftoff Aug. 8. (Please see Space & Missile Defense Report, Monday, Aug. 13, 2007.)

Earlier, foam punched an undetected hole in the leading edge of a wing on Space Shuttle Columbia after a 2003 liftoff. Later, when the spaceship attempted to return to Earth, hot gases of reentry rushed into the wing and heated it to the point of structural failure. The ship and crew were lost.

So the imminent Discovery mission will have Parazynski and Wheelock test how to repair test tiles while in orbit, tiles that have been damaged deliberately.

During a spacewalk, they will pump repair goo into the damaged areas, using something like a caulk gun.

After Discovery goes through the blistering heat of reentry and lands, technicians will examine how well the repairs can hold up to that rough treatment.

Ideally, Discovery can lift off on schedule Oct. 23, because it is important for NASA to stick to its manifest of scheduled missions to complete construction of the International Space Station (ISS).

The Discovery STS-120 Mission will be the 23rd to the ISS, delivering the Node 2 Harmony module that will expand the ISS capability to accept hookups of future international laboratories such as Columbus.

Only the space shuttles have the size and moxie to hoist huge components into space. But the shuttle fleet is slated to retire in 2010.

After Discovery, the next mission is not even two months later, with Space Shuttle Atlantis set to lift off Dec. 6. That STS-122 Mission will deliver the Columbus European Laboratory Module to hook up to Node 2.