Engineers Still Eyeing APU Problems

Space Shuttle Discovery ended STS-121’s stay at the International Space Station when it undocked Saturday morning at 6:08 a.m. EDT. Undocking occurred as the two spacecraft flew above the Pacific Ocean north of New Zealand.

STS-121 delivered a new Expedition 13 crew member and much needed supplies and equipment to the international outpost. The shuttle crew also conducted three spacewalks to perform maintenance on the station and to test on-orbit heat shield repair techniques.

Pilot Mark Kelly flew Discovery to a point above the station before performing the final separation burn at 6:57 a.m.

STS-121 crew members are using the robotic arm and the orbital boom sensor system to perform final inspections of the starboard wing and the shuttle nose cap. Discovery will remain about 45 miles behind the station until the mission management team reviews survey results and clears it for landing... which Kelly says he fully expects to occur.

"Based on what we've seen over the last ten days, the inspections we've done, we've got a great ship," said Kelly. "It's ready to come home."

NASA is still keeping its eyes on a potential problem -- not with the heat shield, but with two of the three auxiliary power units. As Aero-News reported Friday, one has seen a near-total loss of pressure, while the other's backup generator has failed.

Fortunately, that's why the shuttle has those much-vaunted "triple-redundant" systems -- as NASA says one fully functional APU is all that's needed for the orbiter to return to Earth safely.

As it stands, Discovery is scheduled to touch down at Florida's Kennedy Space Center at 9:14 am EDT Monday.

FMI: www.nasa.gov