SpaceX COTS Demo Flight 2 (COTS 2), also known as Dragon C2+, was the second test-flight for SpaceX's uncrewed Cargo Dragon spacecraft. It launched in May 2012 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, Dragon 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.
History
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 Flight 1, 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.
Original plan Under the original Dragon testing plan, the C2 and C3 missions would have been flown instead of C2+. C2 would have rendezvoused with the ISS, however it would not have performed the capture and berthing part of the mission. The third test-flight was intended to be Dragon's first mission to berth with the ISS. Following a 15 July 2011 meeting between SpaceX and NASA officials, the COTS 3 mission objectives were tentatively combined with the proposed COTS 2 demonstration flight, due to the Falcon 9's two previously successful launches, and the Space Shuttle fleet recently being retired.
On 9 December 2011, NASA formally approved the two missions' merger, and set the initial launch date for 7 February 2012. Several delays occurred between December and May 2012, mostly due to SpaceX needing to further test hardware and software. The Dragon C2+ mission successfully launched on 22 May, from Cape Canaveral Launch Complex 40 (SLC40). It successfully completed all COTS 2 mission objectives, then berthed with the ISS, and completed all COTS 3 mission objectives, before successfully splashing down in the Pacific Ocean, off the California coast on 31 May. Since all COTS objectives were met during the Dragon C2+ flight in May 2012, the need for COTS Demo Flight 3 was eliminated.
Mission timeline
Flight day 1, launch (22 May)
Launch occurred at 03:44 EDT (07:44UTC) on 22 May 2012. This was the first time a Falcon 9 was launched at night. After lift-off, main engine shut-off occurred at approximately the 180-second mark, and the first stage began to be separated. Following stage separation, the second stage ignited. The Dragon's nose cone was then jettisoned. And at about nine minutes into the flight, the second-stage engine shut-off occurred and separated from the Dragon spacecraft. The Dragon spacecraft successfully deployed its solar arrays at about 13 minutes into the flight.
The initial COTS 2 tests began during this flight segment, when Dragon performed a test of its Absolute GPS (AGPS) system, using global positioning system satellites to determine its location. Next, Dragon opened its bay door which housed its grapple fixture and relative navigation sensors, a thermal imager and the LIDAR based DragonEye. After a checkout of these sensors was completed, Dragon demonstrated its ability to abort during an approach, first with a continuous firing of its Draco engines and then with a pulsed firing. A free drift demonstration then began, allowing the spacecraft to float freely without using its thrusters which would normally correct its orbital path.
Flight day 2 (23 May)
On flight day two, Dragon began a series of thruster burns, called "height adjustment" burn (HA-1), and "co-elliptical" burn (CE-1). The CE-1 burn changed Dragon's orbit characteristics by placing it into a circular orbit around the Earth. The HA-1 burn raised Dragon's altitude to within a few kilometres below the ISS, in preparation for the next day's rendezvous demonstration.
Flight day 3 (24 May)
On flight day three, Dragon performed height adjustment burn 2 (HA-2) at 07:58UTC, to get within about of the ISS, the "communication zone." At 08:43UTC co-elliptical burn 2 (CE-2) raised its orbit to nearly the same plane as the ISS, and brought it to within below the station. During this "fly-under," Dragon established communications with the station using its COTS Ultra-high frequency Communication Unit (CUCU). Dragon performed a test of its Relative GPS (RGPS) system, which used the relative positions of the spacecraft to the space station to determine its location. Also, using the Crew Command Panel (CCP) on board the Cupola module, the Expedition 31 crew briefly interacted with Dragon, monitoring the fly-under and just before 11:00UTC sending a command to Dragon to turn on its strobe light. At about 11:25UTC the Dragon made its closest approach to the ISS. Once the fly-under was completed, Dragon fired its thrusters to begin a loop out in front, above and then behind the station in a racetrack oval pattern at a distance between . The Dragon performed a final burn for the day, at 11:57UTC, that moved it away from the ISS, and set the spacecraft up for a re-rendezvous with the station the next day. After Dragon cleared the station's vicinity, NASA approved the berthing to occur on day 4, meaning all the original COTS 2 mission requirements were met.
Flight day 4 (25 May)
On flight day four, Dragon performed HA-3 and CE-3 thruster burns to bring it below the station once again. NASA's Mission Control Houston team then gave SpaceX the go ahead to perform another set of burns that brought Dragon to within of the station. Another decision was made at Mission Control Houston, and then Dragon moved to from the station. At this point, the COTS 3 demonstration objectives began. Dragon's DragonEye system demonstrated and confirmed that its position and velocity were accurate by comparing its LIDAR image to its thermal imagers. A series of checkout maneuvers commenced. The SpaceX flight control team in Hawthorne, California, commanded the spacecraft to approach the station from its hold position. It moved from below the station. The crew, using the command panel, then instructed Dragon to retreat, and the spacecraft moved back down to the hold point. This test ensured that Dragon's range to the ISS was accurate, and that the flight control team saw the spacecraft's acceleration and braking perform as expected. It was in a holding pattern at , and once again the Dragon flight team commanded it to approach the station. At the position, the crew commanded the vehicle to hold.
Another decision was made in Houston, and Dragon was permitted to enter the Keep-Out Sphere (KOS), a virtual area around the station intended to prevent collision with the orbiting complex. Two additional and non-planned holds occurred: one at to further verify LIDAR; and finally one by SpaceX at to re-configure the LIDARs. Stray reflections from the JAXA JEM module's External Facility (EF) caused interference with the LIDAR; SpaceX decided to narrow the LIDAR's field-of-view to eliminate the reflections.
Dragon proceeded to a position from the station and automatically came to a stop for a hold. Another decision was made, and then Dragon proceeded to the capture point position at . A final decision was made, and the Mission Control Houston team notified the crew they were go to capture Dragon. At that point, from the Cupola module, Expedition 31 crew member Don Pettit used the station's Mobile Servicing System (Canadarm2) to reach out and grapple the Dragon spacecraft at 13:56UTC over Western Australia. Upon capture, Pettit jokingly told ISS CAPCOM Megan McArthur, "Looks like we got us a Dragon by the tail. We're thinking this sim went really well, we're ready to turn it around and do it for real." Pettit, with the help of fellow crewmember André Kuipers, guided and then berthed Dragon to the Harmony module's Earth-facing Common Berthing Mechanism at 16:02UTC.
Flight day 5 and remainder of mission (26 to 31 May)