The STS-121 crew was first named in December 2003 after the flight was added to the space shuttle schedule to help accommodate the growng list of requirements originally assigned to the first Return to Flight mission, STS‐114. The initial crew included Commander Steven W. Lindsey, an Air Force colonel, Pilot Mark E. Kelly, a Navy commander, and mission specialists Carlos I. Noriega and Michael E. Fossum. Noriega was replaced by Piers J. Sellers in July 2004 because of a temporary medical condition.

Mission specialists Lisa M. Nowak, a Navy commander, and Stephanie D. Wilson were added to the flight in November 2004. The mission was declared a crew rotation flight when NASA determined returning to a three‐person crew aboard the International Space Station would be possible following the first two shuttle supply missions. Thomas Reiter was added to the flight in July 2005.

 

Commander Steven Lindsey is a veteran of three spaceflights and a second‐time commander who has overall responsibility for the on-orbit execution of the mission, orbiter systems operations, and flight operations including landing the orbiter. In addition, he will fly the shuttle in a procedure called the rendezvous pitch maneuver while Discovery is 600 feet below the station before docking to enable the ISS crew to photograph the orbiter's heat shield. He will then dock Discovery to the station. He will also be heavily involved in inspections of Discovery’s heat shield and transferring cargo to and from the shuttle

Pilot Mark Kelly is flying for the second time and will be responsible for systems operations and assisting in the rendezvous and docking to the International Space Station. He will also serve as the intravehicular activity crew member helping to suit up and choreograph spacewalkers Piers Sellers ad Michael Fossum during their spacewalks. In addition, he will be heavily involved in inspections of Discovery’s heat shield and transferring cargo to and from the shuttle. He will undock Discovery from the station at the end of the mission.

Mission Specialist 1 (MS1) Michael Fossum will make his first venture into space. Fossum will perform two to three spacewalks, as EV2 with his colleague Piers Sellers, to test shuttle heat shield inspection and repair techniques. Testing will include evaluating the robotic boom extension as a work platform and testing repair materials and hardware for damaged shuttle heat shield components. He will also continue International Space Station assembly by replacing failed hardware and installing spare parts on the outide of the complex. Fossum will also assist with inspections of Discovery’s heat shield. Fossum will be seated on the flight deck for launch and the middeck for landing.

Mission Specialist 2 (MS2) is astronaut Lisa Nowak, making her first flight into space. She will serve as the flight engineer on STS-121, adding a second set of eyes on orbiter systems for the commander and the pilot on the flight deck during launch and landing. As a robotic arm operator, she will maneuver her crewmates and hardware during the two to three spacewalks using the shuttle arm on the first and the staion arm for the second and third spacewalks. She will also perform heat shield inspections with the orbiter boom sensor system and use the station robotic arm to handoff he boom to the shuttle arm. During the rendezvous, docking and undocking, she will manage computers, lasers, cameras, and the orbiter docking system.

Mission Specialist 3 (MS3) is astronaut Stephanie Wilson. She is making her first flight into space. She will serve as the overall lead for transferring supplies from the shuttle's cargo module to the station. She also will serve as a robotic arm operator, using the space station robotic arm to install the Leonardo cargo module onto the station and to handoff the boom to the shutte arm, and use the orbiter boom sensor system to inspect Discovery’s heat shield. Prior to the spacewalks, she will assist with suit‐up of the spacewalkers. During the rendezvous, docking and undocking, she will manage the handheld laser and the orbiter docking system. Wilson will be seated on the middeck for launch and the flight deck for landing.

Mission Specialist 4 (MS4) is astronaut Piers Sellers, a veteran of one spaceflight. His main objective is to lead and perform two to three spacewalks, as EV1 along with his spacewalking colleague, Michael Fossum. During the spacewalks, they will test shuttle heat shield inspection and repair techniques. Testing will include evaluation of the robotic boom extension as a work platform and testing of repair materials and hardwarefor damaged heat shield components. He will also continue International Space Station assembly by replacing failed hardware and installing spare parts on the outide of the complex. Sellers will be seated on the middeck for launch and landing.

International Space Station Flight Engineer Thomas Reiter (FE2), representing the European Space Agency (ESA), is flying to the space station aboard Discovery. He will lead the transfer of supplies from the shuttle's cargo module to the space station during the spacewalks and he will assist with suit‐up prior to the spacewalks. He is conducting his second long‐duration spaceflight mission. He spent 179 days in space in 1995-1996 on a mission to the Russian Mir space station during which he conducted two spacewalks and about 40 European scientific exeriments. Reiter is the first ESA astronaut to live aboard the International Space Station for a long‐term mission. Reiter will work on the station as part of an agreement between the Russian Federal Space Agency and ESA. Reiter will be on the middeck for launch and remain on the space station until the STS-116 space shuttle, or a Soyuz, mission.