NASA has announced that the last space shuttle mission - Endeavour's STS-134 to the International Space Station - will now lift off on 26 February next year.

Discovery's STS-133 mission, meanwhile, is scheduled for 1 November. NASA explains: "The target dates were adjusted because critical payload hardware for the STS-133 mission will not be ready in time for the previously targeted date. With Discovery's move, Endeavour had to plan for its next available window, which was February."

The critical payload hardware in question is the Alpha Magnetic Spectrometer (AMS). Following the extension of the ISS's working life to 2020, scientists decided to "change out the current magnet in the particle physics experiment module that will be attached to the International Space Station to a longer lasting one"

STS-133 will "deliver and install the Permanent Multipurpose Module, the Express Logistics Carrier 4 and provide critical spare components" to the ISS.

STS-134 will carry "spare parts including two S-band communications antennas, a high-pressure gas tank, additional spare parts for Dextre and micrometeoroid debris shields". ®