Pictures: Virgin Galactic SpaceShipTwo VSS Unity

Virgin Galactic’s SpaceshipTwo (right) launches for a suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

A jet carrying Virgin Galactic’s tourism space ship takes off from Mojave Air and Space Port on Thursday, Dec. 13, 2018 in Mojave, Calif. The jet climbed to an altitude near 43,000 feet and then released Virgin Space Ship Unity. The pilots flew the rocket ship to an altitude exceeding 50 miles (80 kilometers), which Virgin Galactic considers the boundary of space.

Virgin Galactic’s SpaceshipTwo launches for a suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

Virgin Galactic’s SpaceshipTwo launches for a suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

Virgin Galactic’s SpaceshipTwo launches for a suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

Virgin Galactic’s SpaceshipTwo launches for a suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

Virgin Galactic’s VSS Unity comes in for a landing after its suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

Virgin Galactic’s VSS Unity comes in for a landing after its suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

Virgin Galactic’s SpaceshipTwo launches for a suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

Virgin Galactic’s VSS Unity comes in for a landing after its suborbital test flight on Dec. 13, 2018, in Mojave, California. Virgin Galactic marked a major milestone as its space ship made it to a peak height, or apogee, of 51.4 miles after taking off attached to an airplane from Mojave, California, then firing its rocket motors to reach new heights.

In this Sept. 25, 2013, file photo, British entrepreneur Richard Branson poses with the first SpaceShipTwo at a Virgin Galactic hangar at Mojave Air and Space Port in Mojave, Calif. Virgin Galactic will roll out a new copy of its space tourism rocket Friday, Feb. 19, 2016, as it prepares to resume flight testing for the first time since a 2014 accident destroyed the original and killed one of its two pilots.

In this Sept. 25, 2013, file photo, the first SpaceShipTwo is seen suspended at center beneath its twin-fuselage mother ship at the Virgin Galactic hangar at Mojave Air and Space Port in Mojave, Calif. Virgin Galactic will roll out a new copy of its space tourism rocket Friday, Feb. 19, 2016, as it prepares to resume flight testing for the first time since a 2014 accident destroyed the original and killed one of its two pilots.

In this Nov. 1, 2014 file photo, wreckage lies near the site where a Virgin Galactic space tourism rocket, SpaceShipTwo, crashed in the desert near Mojave, Calif. One of the two pilots aboard was killed. Virgin Galactic will roll out a new copy of its space tourism rocket as it prepares to resume flight testing for the first time since the 2014 accident destroyed the original. The new spacecraft will be unveiled at Mojave Air and Space Port in Mojave Friday, Feb. 19, 2016.

Sir Richard Branson speaks to AFP during an interview before the official unveiling of Virgin Galactic’s SpaceShipTwo, the world’s first commercial manned spacecraft, at the Mojave Air and Space Port in Mojave, California on December 7, 2009. Previewing the roll-out of the Virgin Galactic craft, the British billionaire said he planned to be on its first passenger flight in about 18 months time with his family and the space ship’s American designer Burt Rutan. Tourists will to pay 200,000 USD a ticket to travel in the in the white port-holed craft suspended under the wings of a mothership dubbed the White Knight.  (ROBYN BECK, AFP/GETTY IMAGES)