STS-128 (ISS assembly flight 17A) was a space shuttle mission to the International Space Station (ISS). It is using Space Shuttle Discovery, and launched on 28 August 2009. The primary payload is the Multi-Purpose Logistics Module Leonardo, containing a collection of experiments for studying the physics and chemistry of microgravity. Three spacewalks are planned during the mission, which will remove and replace a materials processing experiment outside ESA's Columbus module, and to return an empty ammonia tank assembly. The first launch attempt was delayed due to weather concerns, including multiple weather violations in NASA's launch rules, beginning over 2 hours before the scheduled launch. The second launch attempt scheduled for August 26, at 1:10:22 AM EDT was called off the previous evening due to an anomaly in a fuel valve of the orbiter. The launch took place on Friday, August 28 at 11:59 PM EDT.