SpaceShipTwo
The Scaled Composites Model 339 SpaceShipTwo is a retired air-launched suborbital spaceplane type designed for space tourism. It was manufactured by The Spaceship Company, a California-based company owned by Virgin Galactic.
SpaceShipTwo was carried to its launch altitude by a Scaled Composites White Knight Two, before being released to fly on into the upper atmosphere powered by its rocket engine. It then glided back to Earth and performed a conventional runway landing. The spaceship was officially unveiled to the public on 7 December 2009 at the Mojave Air and Space Port in California. On 29 April 2013, after nearly three years of unpowered testing, the first SS2 constructed successfully performed its first powered test flight.
Virgin Galactic planned to operate a fleet of five SpaceShipTwo spaceplanes in a private passenger-carrying service and took bookings for some time, with a suborbital flight carrying a ticket price of US$250,000 in 2015. The spaceplane was also used to carry scientific payloads for NASA and other organizations.
On 31 October 2014, during a test flight, the first SpaceShipTwo VSS Enterprise broke up in flight and crashed in the Mojave Desert. An investigation found that the craft's descent device deployed too early. One pilot, Michael Alsbury, was killed; the other was treated for a serious shoulder injury after parachuting from the stricken spacecraft.
The second SpaceShipTwo spacecraft, VSS Unity, was unveiled on 19 February 2016. The vehicle underwent flight testing 2016-2023. Its first flight to space, VSS Unity VP03, took place on 13 December 2018. The first operational flight of Unity was Galactic 01 on 29 June 2023. The final flight of Unity was Galactic 07 on 8 June 2024.
Design overview
The SpaceShipTwo project was based in part on technology developed for the first-generation SpaceShipOne, which was part of the Scaled Composites Tier One program, funded by Paul Allen. The Spaceship Company licensed this technology from Mojave Aerospace Ventures, a joint venture of Paul Allen and Burt Rutan, the designer of the predecessor technology.SpaceShipTwo was a low-aspect-ratio passenger spaceplane. Its capacity was planned to be eight people — six passengers and two pilots. The SpaceShipTwo spaceplanes never flew with more than 6 people onboard. The apogee of the new craft was designed to be approximately in the lower thermosphere, higher than the Kármán line but as of July 2021, the maximum height reached was 89.9 km. In the end, the SpaceShipTwos never broke the 100 km limit. The predecessor craft SpaceShipOne's target was also 100 km but the last flight reached an altitude of. SpaceShipTwo was designed to reach, using a single hybrid rocket engine — the RocketMotorTwo. It launched from its mothership, White Knight Two, at an altitude of, and reached supersonic speed within 8 seconds. After 70 seconds, the rocket engine cut out and the spacecraft coasted to its peak altitude. SpaceShipTwo's crew cabin was long and in diameter. The wing span was, the length was and the tail height was.
SpaceShipTwo used a feathered reentry system, feasible due to the low speed of reentry. In contrast, orbital spacecraft re-enter at orbital speeds, close to, using heat shields. SpaceShipTwo was furthermore designed to re-enter the atmosphere at any angle. It decelerated through the atmosphere, switching to a gliding position at an altitude of, and took 25 minutes to glide back to the spaceport.
SpaceShipTwo and White Knight Two were, respectively, roughly twice the size of the first-generation SpaceShipOne and mothership White Knight, which won the Ansari X Prize in 2004. SpaceShipTwo had -diameter windows for the passengers' viewing pleasure, and all seats reclined back during landing to decrease the discomfort of G-forces. In 2008, Burt Rutan remarked on the safety of the vehicle:
In September 2011, the safety of SpaceShipTwo's feathered reentry system was tested when the crew briefly lost control of the craft during a gliding test flight. Control was reestablished after the spaceplane entered its feathered configuration, and it landed safely after a 7-minute flight.
Fleet and launch sites
Fleet history
SpaceShipTwo were built by The Spaceship Company, originally formed as a joint venture between Scaled Composites and Virgin Galactic. Virgin Galactic bought out Scaled Composites' interest in TSC in 2012, and TSC became a wholly owned subsidiary of Virgin Galactic.The launch customer of SpaceShipTwo was Virgin Galactic, who as of 2005 had publicly announced they had ordered five vehicles, but only three had been ordered by 2015. The first SS2 was named VSS Enterprise. The "VSS" prefix stands for "Virgin Space Ship". VSS Enterprise was the first to fly; it was destroyed in a crash on 31 October 2014. The build of VSS Unity was about 65% complete in early November 2014, and Virgin Galactic expected it to be complete in 2015. It was unveiled in February 2016 and performed its first powered flight in April 2018. The third SpaceShipTwo was expected to commence construction by the end of 2015.
Unity was retired on 8 June 2024 after its final flight took place on that date, as Virgin Galactic shifted its focus to the next generation Delta-class vehicles. At the time, the only SpaceShipTwos completed and flown were the Enterprise and the Unity.
Launch sites
SpaceShipTwo was launched from the WhiteKnightTwo launcher aircraft, which took off from the Mojave Air and Space Port in California during testing. Spaceport America, a US$212 million spaceport in New Mexico, partly funded by the state government, became the permanent launch site for the latter part of test flight programme and for commercial launches.Ships in class
Two further ships were under construction by 2016. It is unclear whether these are now designated to be SpaceShip III class vehicles. As of 2024, the only SpaceShipTwo-class vehicles completed and flown are Enterprise and Unity.Development
On 28 September 2006, Virgin Group founder Sir Richard Branson unveiled a mock-up of the SpaceShipTwo passenger cabin at the NextFest exposition at the Jacob K. Javits Convention Center in New York. The design of the vehicle was revealed to the press in January 2008, with the statement that the vehicle itself was around 60% complete. On 7 December 2009, the official unveiling and rollout of SpaceShipTwo took place. The event involved the first SpaceShipTwo being christened by then - Governor of California Arnold Schwarzenegger as the VSS Enterprise.2007 test explosion
On 26 July 2007, an explosion occurred during an oxidizer flow test at the Mojave Air and Space Port, where early-stage tests were being conducted on SpaceShipTwo's systems. The oxidizer test included filling the oxidizer tank with of nitrous oxide, followed by a 15-second cold-flow injector test. Although the tests did not ignite the gas, three employees were killed and three injured by flying shrapnel.Rocket engine
The hybrid rocket engine design for SpaceShipTwo was problematic and caused extensive delays to the flight test program. The original rocket engine design was based on hydroxyl-terminated polybutadiene fuel and nitrous oxide oxidizer, sometimes referred to as an N2O/HTPB engine. It was developed by Scaled Composites subcontractor Sierra Nevada Corporation from 2009 to early 2014. In May 2014, Virgin Galactic announced a change to the hybrid engine to be used in SpaceShipTwo, and took the development effort in-house to Virgin Galactic, terminating the contract with Sierra Nevada and halting all development work on the first-generation rocket engine. Virgin then modified the engine design to include a change of the hybrid rocket fuel from a HTPB to a polyamide fuel formulation. In October 2015, Virgin announced that it was considering changing back to the original HTPB fuel.2014 change of engine
Rather than the rubber-based HTPB-fuel engine—engines that had experienced serious engine stability issues on firings longer than approximately 20 seconds — the engine would instead be based on a solid fuel composed of a type of plastic called thermoplastic polyamide. The plastic fuel was projected to have better performance and was projected to allow SpaceShipTwo to make flights to a higher altitude.when the version 2 engine by Virgin Galactic was publicly announced, the engine had already completed full-duration burns of over 60 seconds in ground tests on an engine test stand. The second-generation engine design also required the modification to the SS2 airframe to fit additional tanks in the wings of SpaceShipTwo — one holding methane and the other containing helium — in order to ensure a proper burn and shut-down of the new engine. Additional ground tests were performed on the new engine between May and October 2014.