The launch of the Discovery shuttle on the STS-128 mission to the International Space Station (ISS) has been postponed to August 28 2009 after two consecutive delays due to bad weather and technical issues.

Over the 13-day mission, the spacecraft will transport equipment to the ISS, including a materials science laboratory that will investigate basic production processes of metallic alloys and semiconductors and measure their thermophysical properties.

Discovery will also fly Declic, a multi-user facility for research fluid physics and the second unit of the space freezer Melfi on a multipurpose logistics module named Leonardo.

The first delay for the scheduled launch on 25 August 2009 was caused by lingering thunderstorms in the vicinity of the launch pad. The second delay occurred after a valve problem was detected in the shuttle’s aft compartment during tanking operations.

Detailed test data about the valve will be examined before the spacecraft’s fuel tank is loaded with propellant ahead of the third launch attempt.