Return to Flight" sensor tests. Engineer's hand holding the container for a space shuttle sensor, with the motherboard seen in front of it. This is a sensor similar to the one that failed and caused the abandonment of the 13 July 2005 launch of the space shuttle Discovery. The sensor that failed was one that monitored the levels of fuel in the main external fuel tank. The launch was part of mission STS-114, "Return to Flight", the first flight of a space shuttle since the space shuttle Columbia broke up on re-entry in February 2003. The sensor design is being tested. If it is found to be safe then the shuttle may still return to flight before its launch window ends on 31 July 2005."