In Orbiter Processing Facility Bay 3 workers install the new orbital boom sensor system in Discovery's bay.

In Orbiter Processing Facility Bay 3, workers install the new orbital boom sensor system in Discovery’s payload bay. The previous boom was removed for repairs on the manipulator positioning mechanism, the pedestals that hold the boom in place in the payload bay. Discovery is the designated orbiter for the second return-to-flight mission, STS-121. The mission is scheduled no earlier than mid-May.