Dragon C2+, also known as SpaceX COTS Demo Flight 2 (COTS 2), was the second test-flight for SpaceX's uncrewed Dragon cargo spacecraft, launched on the third flight of the company's two-stage Falcon 9 launch vehicle. The flight was performed under a funded agreement from NASA as the second Dragon demonstration mission in the Commercial Orbital Transportation Services (COTS) program. The purpose of the COTS program is to develop and demonstrate commercial sources for cargo re-supply of the International Space Station (ISS). The Dragon C2+ spacecraft was the first American vehicle to visit the ISS since the end of the Space Shuttle program. It was also the first commercial spacecraft to rendezvous and berth with another spacecraft.
Initially, the objectives of the C2+ mission were to have been accomplished by two separate missions; Dragon C2 would have carried out a fly-by of the ISS, practiced rendezvous maneuvers and communications with the station, before returning to Earth. A second mission, C3, would have been the first mission to berth with the station. In July 2011, NASA gave tentative approval to combine the objectives of the two missions. In December 2011, NASA formally approved the merger of the COTS 2 and 3 missions into the Dragon C2+ flight. There were several launch delays, the last one occurring on 19 May 2012, due to a launch abort during the last second before liftoff.
Dragon C2+ successfully launched from Cape Canaveral on 22 May 2012. During the mission's first three days all of the COTS 2 objectives were successfully completed. The mission's COTS 3 phase began on 25 May when Dragon rendezvoused again with the ISS and then was successfully captured using the Canadarm2. It was berthed to the station later that day, using the robotic arm. Dragon stayed for almost six days during which the astronauts unloaded cargo, and then reloaded Dragon with Earth-bound cargo. On 31 May, Dragon unberthed from the ISS, its capsule landed in the Pacific Ocean off the California coast and was recovered. All the objectives of the mission were successfully completed, and the Falcon 9-Dragon system became certified to start regular cargo delivery missions to the ISS under the Commercial Resupply Services program.
NASA and SpaceX signed a contract for COTS cargo resupply services on 18 August 2006. The agreement called for three test-flights, under the COTS phase 1 demonstration program. The first COTS mission, COTS Demo Flight1, was completed successfully on 8 December 2010, when the Dragon capsule was successfully recovered from orbit, making it the first commercially built and operated spacecraft to ever do so. Due to the mission's success, SpaceX asked NASA to combine the COTS 2 ISS flyby flight, which would have seen a Dragon spacecraft approach the station but stay about 10 km away from it, and the COTS 3 flight that would berth with the ISS. At a 15 July 2011 meeting, NASA tentatively approved combining the two COTS missions to accelerate the program into the operational supply mission phase in 2012. On 9 December, NASA officially approved the merger of the COTS 2 and 3 missions into the renamed Dragon C2+ flight.
The Falcon 9 launch vehicle arrived at SpaceX's Cape Canaveral, Florida facilities at Launch Complex 40 (LC-40) in July 2011. The mission's Dragon spacecraft arrived at the launch site on 23 October 2011. On 1 March 2012, a fueled countdown test called a Wet Dress Rehearsal (WDR), was successfully completed for the COTS 2 mission. On 16 April its Flight Readiness Review (FRR) was completed by NASA and stated that a 30 April launch was feasible. Following the review SpaceX announced a launch delay, due to continued flight software testing issues, and the next major mission milestone was the successful Falcon 9 static-fire engine test on 30 April. NASA approved Dragon's flight software on 11 May, solving an issue that had previously been responsible for several launch date postponements. On 17 May, the mission passed its final launch review and the Falcon 9/Dragon were erected on the launch pad in preparation for the launch. The first launch attempt, on 19 May, was aborted at T-00:00:00.5 due to a pressure issue in one of the Falcon 9's engines. The launch window was nearly instantaneous, for fuel-efficiency reasons, leaving little margin for error due to fuel consumption restrictions caused by the extra manoeuvres required to certify the Dragon spaceship before attempting to berth with the ISS. Dragon's launch window could have been longer, but the extra fuel required to catch the ISS would have likely surpassed safety margins, due to the pre-berthing tests.