Given an expected gap of five years between operational readiness for the Ares I crew launch vehicle in 2015 and the expected retirement of the Space Shuttle in 2010, NASA in 2006 created the COTS commercial transport programme to spur private industry to develop rockets and spacecraft that could resupply the International Space Station with cargo and crew.
After an initial selection of two companies - Space Exploration Technologies and Rocketplane-Kistler - Orbital Sciences replaced the latter after it missed a programme milestone, and the three companies have shared in the $500 million funding allocated to COTS. NASA has not exercised the COTS option to develop the commercial vehicles to carry crews. In December, the agency awarded $3.5 billion in contracts to the same two companies as part of a cargo resupply services programme.
Both companies will carry 20,000kg (44,000lb) in supplies to the ISS between 2010 and 31 December 2016, taking away an undetermined amount of waste and equipment to be returned to Earth.