reusable spaceplane using a crewed fly-back booster. This concept proved expensive and complex, therefore the design was scaled back to reusable solid rocket boosters and an expendable external tank. Space Shuttle Columbia launched and landed 27 times and was lost with all crew on the 28th landing attempt; Challenger launched and landed 9 times and was lost with all crew on the 10th launch attempt; Discovery launched and landed 39 times; Atlantis launched and landed 33 times. In 1986 President Ronald Reagan called for an air-breathing scramjet National Aerospace Plane (NASP)/X-30. The project failed due to technical issues and was canceled in 1993. In the late 1980s a fully reusable version of the Energia rocket, the Energia II, was proposed. Its boosters and core would have had the capability of landing separately on a runway. In the 1990s the McDonnell Douglas Delta Clipper VTOL SSTO proposal progressed to the testing phase. The DC-X prototype demonstrated rapid turnaround time and automatic computer control. In mid-1990s, British research evolved an earlier HOTOL design into the far more promising Skylon design, which remains in development. From the late 1990s to the 2000s, the European Space Agency studied the recovery of the Ariane 5 solid rocket boosters. The last recovery attempt took place in 2009. The commercial ventures, Rocketplane Kistler and Rotary Rocket, attempted to build reusable privately developed rockets before going bankrupt. NASA proposed reusable concepts to replace the Shuttle technology, to be demonstrated under the X-33 and X-34 programs, which were both cancelled in the early 2000s due to rising costs and technical issues. 21st century The Ansari X Prize contest was intended to develop private suborbital reusable vehicles. Many private companies competed, with the winner, Scaled Composites, reaching the Kármán line twice in a two-week period with their reusable SpaceShipOne. In 2012, SpaceX started a flight test program with experimental vehicles. These subsequently led to the development of the Falcon 9 reusable rocket launcher. On 23 November 2015 the New Shepard rocket became the first Vertical Take-off, Vertical Landing (VTVL) sub-orbital rocket to reach space by passing the Kármán line (), reaching before returning for a propulsive landing. SpaceX achieved the first vertical soft landing of a reusable orbital rocket stage on December 21, 2015, after delivering 11 Orbcomm OG-2 commercial satellites into low Earth orbit. The first reuse of a Falcon 9 first stage occurred on 30 March 2017. SpaceX