After assessing payload processing issues and projected traffic to and from the International Space Station, NASA managers Thursday formally retargeted the program's final two missions for launches Nov. 1 and Feb. 26.

Credit: NASA

The shuttle Discovery, which had been scheduled for launch Sept. 16 on mission STS-133, is now targeted for liftoff at 4:33 p.m. EDT on Nov. 1. The primary goals of the two-spacewalk mission are to deliver spare parts and supplies, along with a modified cargo transfer module that will be permanently attached to the station to provide additional storage space.

The shuttle Endeavour, which had been targeted for launch around Nov. 26, was reset for takeoff at 4:19 p.m. EST on Feb. 26, 2011. The goal of that mission is to deliver the $1.5 billion Alpha Magnetic Spectrometer to the station, along with a pallet of critical spare parts that will be mounted on the lab's power truss.

NASA managers asked engineers to reassess the launch dates with an official "change request" that went out June 22. At that time, the proposed target dates were Oct. 29 for STS-133 and Feb. 28 for STS-134.

The STS-133 slip was required to complete preparations of critical spares that will be launched in the Permanent Multi-Purpose Module, or PMM, including a pump package, a robotic test article known as "Robonaut" and a heat exchanger. Other hardware required for the Alpha Magnetic Spectrometer and spares for the station's life support system also were on tight schedules.

Two Russian launches planned for October forced NASA to consider the Oct. 29 target. Then, during the review process, planners realized the target date was in conflict with an already scheduled air show and maintenance planned at the Air Force Range that provides tracking and telemetry support for all rockets launched from Florida. As a result, agency managers settled on Nov. 1.

Assuming the schedule holds up, commander Steven Lindsey pilot Eric Boe, station veterans Nicole Stott and Michael Barratt and spacewalkers Alvin Drew and Timothy Kopra, another station veteran, will blast off from pad 39A at 4:33 p.m. on Nov. 1. Docking with the International Space Station would be expected around 12:52 p.m. on Nov. 3.

The PMM would be installed on Nov. 4, followed by spacewalks with Kopra and Drew on Nov. 5 and 7. Undocking would be targeted for 7:13 a.m. on Nov. 10 with landing back at the Kennedy Space Center on tap around 12 p.m. Friday, Nov. 12.

Endeavour's launching on mission STS-134 originally was scheduled for July, but the flight was delayed to late November after a decision to replace the magnet at the heart of the Alpha Magnetic Spectrometer. The AMS payload will not be delivered to the Florida space center until late August and three months of on-site processing are required before launch.

A late-November/early December launch was ruled out because of conflicts with other planned station launches. Temperature constraints related to the station's orbit prevented a launch in January and range conflicts with other unmanned missions pushed the approved launch date to Feb. 26.

Endeavour will be commanded by veteran Mark Kelly. His crewmates are pilot Gregory Johnson, Hubble veteran Andrew Feustel, European Space Agency astronaut Roberto Vittori and station veterans Gregory Chamitoff and Mike Fincke.

NASA originally planned to end shuttle operations by the end of fiscal 2010, launching Endeavour in July followed by Discovery in mid September. But Congress already had promised an additional $600 million to cover shuttle costs through the end of the calendar year to avoid the sort of schedule pressure blamed in part for the Challenger and Columbia mishaps.

NASA managers then came up with additional savings, permitting operations through February or March without additional appropriations.

The shuttle Atlantis is being processed to serve as an emergency rescue vehicle for Endeavour's crew. But if a rescue flight is not needed, NASA managers believe the standby shuttle could be launched with a crew of four, relying on Russian Soyuz capsules to ferry the crew members home if a major problem blocked a safe re-entry.

Concerned about the near-term lack of a large rocket to deliver heavy payloads after the shuttle fleet is retired, NASA managers want to take advantage of the boosters and external tank being prepared for Atlantis' rescue mission that otherwise would go to waste.

But additional funding would be required and it's not yet clear whether NASA has the necessary political support. A decision is expected in August.