The Boeing CST-100 Starliner (Crew Space Transportation) is a crew capsule under construction by Boeing as its participation in NASA's Commercial Crew Development (CCDev) program. Its primary purpose is to transport crew to the International Space Station (ISS)[5] and to private space stations such as the proposed Bigelow Aerospace Commercial Space Station.[6]

Starliner is similar in concept to the Orion spacecraft being built for NASA by Lockheed Martin.[7] The capsule has a diameter of 4.56 meters (15.0 ft),[3] which is slightly larger than the Apollo command module and smaller than the Orion capsule.[8] The Starliner is to support larger crews of up to seven people and is being designed to be able to remain on-orbit for up to seven months with reusability of up to ten missions.[9] It is designed to be compatible with four launch vehicles: Atlas V, Delta IV, Falcon 9, and Vulcan.[10]

In the first phase of its CCDev program NASA awarded Boeing US$18 million in 2010 for preliminary development of the spacecraft.[11] In the second phase Boeing was awarded a $93 million contract in 2011 for further spacecraft development.[12] On August 3, 2012, NASA announced the award of $460 million to Boeing to continue work on the CST-100 under the Commercial Crew Integrated Capability (CCiCap) Program.[13] On September 16, 2014, NASA selected the CST-100, along with SpaceX's Crew Dragon, for the Commercial Crew Transportation Capability (CCtCap) program, with an award of $4.2 billion.[14] On July 30, 2019, NASA had no specific dates for Commercial Crew launches, stating that this was under review pending a leadership change.[15]

Starliner's uncrewed test flight launched with the Atlas V N22,[16] on December 20, 2019 from SLC-41 at Cape Canaveral, Florida. During the test, the Starliner experienced an anomaly that precluded a docking with the International Space Station.[17][18]