 Completion of this initial training qualified him for various technical assignments within the Astronaut Office and future flight assignment as a mission specialist.In February 2008 Cassidy was assigned to his first spaceflight as a Mission Specialist on STS-127, a Space Shuttle mission to deliver the Exposed Facility of the Japanese Experiment Module (JEM-EF) to the ISS aboard Space Shuttle "Endeavour".Cassidy and his six fellow crew members lifted off aboard "Endeavour" from the Kennedy Space Center on 15 July 2009, the seven astronauts docked to the ISS on 17 July, joining the six person Expedition 20 crew, commanded by Russian cosmonaut Gennady Padalka, this marked the first time 13 people had been in space together, a record that has not been surpassed since.