Discoveryís launch is scheduled for 3:49 p.m. EDT Saturday. Discovery's STS-121 mission will return the station to three crew members for the first time since 2003, when European Space Agency astronaut Thomas Reiter joins crew members Jeff Williams, flight engineer and Pavel Vinogradov, commander. To get ready for upcoming STS-121 spacewalks, the crew flushed cooling loops in the Quest airlock and U.S. spacesuits, configured airlock systems and tools, and reviewed robotic arm procedures. They checked out a ship-to-ship communications system that will be used for conversations with Discovery's crew during rendezvous and disconnected the stationís Common Cabin Air Assembly heat exchanger. That device will be returned to Earth aboard Discovery along with other equipment in the Italian-built Leonardo Multipurpose Logistics Module. Discovery will bring about 5,000 pounds of supplies to the station carried aboard the logistics module.
The crew also completed a mid-mission session of the renal stone experiment by collecting urine samples and logging all of the food and drinks consumed over a three-day period. Each crewmember is taking either potassium citrate, a drug found to be useful in preventing kidney stone formation on Earth, or a placebo. Crews in space are at risk for kidney stones linked to their loss of bone density.
ISS Progress 22, the unpiloted Russian cargo spacecraft, brought 2.5 tons of fresh produce, other foodstuffs, food, fuel and supplies to the station June 26. After the cargo ship was fully connected with station systems, flight controllers in Moscow completed a routine thruster test and Vinogradov removed its Kurs automated rendezvous hardware.