STS-129 (ISS assembly flight ULF3) was a NASA Space Shuttle mission to the International Space Station (ISS) flown by Atlantis. STS-129 focused on staging spare components outside the station. The 11-day flight included three spacewalks. The payload bay carried two large ExPRESS Logistics Carriers holding two spare gyroscopes, two nitrogen tank assemblies, two pump modules, an ammonia tank assembly, a spare latching end effector for the station's robotic arm, a spare trailing umbilical system for the Mobile Transporter, and a high-pressure gas tank. STS-129 was the first flight of an ExPRESS Logistics Carrier.
The International Space Station programme is tied together by a complex set of legal, political and financial agreements between the sixteen nations involved in the project, governing ownership of the various components, rights to crewing and utilization, and responsibilities for crew rotation and resupply of the International Space Station. It was conceived in 1984 by President Ronald Reagan, during the Space Station Freedom project as it was originally called.