Editing SpaceShipTwo (section)

==== 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 (by several unspecified measures) and was projected to allow SpaceShipTwo to make flights to a higher altitude.<ref name=nsj20140524>{{cite news |last=Foust |first=Jeff |title=Virgin Galactic changes fuels as it prepares for its next round of test flights |url=http://www.newspacejournal.com/2014/05/24/virgin-galactic-changes-fuels-as-it-prepares-for-its-next-round-of-test-flights/ |access-date=25 May 2014 |newspaper=NewSpace Journal |date=24 May 2014 }}</ref><ref name=nbc20140523>{{cite news|last=Boyle|first=Alan|title=Virgin Galactic Makes a Switch in SpaceShipTwo's Rocket Motor|url=https://www.nbcnews.com/storyline/virgin-voyage/virgin-galactic-makes-switch-spaceshiptwos-rocket-motor-n113216|access-date=24 May 2014|publisher=NBC News|date=23 May 2014}}</ref><ref name=aw20140524>{{cite news|title=New Fuel to Boost SpaceShip Two |url=http://www.aviationweek.com/space/new-fuel-boost-spaceship-two|publisher=Aviation Week|date=24 May 2014|last=Morris|first=Guy|access-date=10 December 2015}}</ref>

{{As of|2014|05}} 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.<ref name=nbc20140523/> 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.<ref name=pa20140630>{{cite news|last1=Messier|first1=Doug|title=WhiteKnightTwo in the Air Over Mojave Today |url=http://www.parabolicarc.com/2014/06/30/whiteknighttwo-air-mojave-today/|access-date=1 November 2014|publisher=Parabolic Arc|date=30 June 2014}}</ref> Additional ground tests were performed on the new engine between May and October 2014.