Richard Branson, the eccentric British billionaire owner of the Virgin company, celebrated on Tuesday 13 December a milestone in his space tourism project. The SpaceshipTwo, built by Virgin Galactic, flew into outer space by reaching 51.4 miles (82,720 meters) of altitude on its fourth manned flight, which lasted 60 seconds at a maximum speed of Mach 2.5.

Released at about 50,000 feet by White Night, SpaceshipTwo is then driven by its hybrid rocket engine to accelerate at supersonic speeds and reach a level considered suborbital flight.

The flight on Thursday was piloted by Mark “Forger” Stucky and Frederick “CJ” Sturckow, the latter a former NASA astronaut who participated in four missions aboard the Space Shuttle.

Speaking of NASA’s retired spacecraft, it was the first time a manned US spacecraft had made its way to space since the end of Space Shuttle missions in 2011. In addition, never before has a commercial and civilian space vehicle hit space.

The Earth seen from more than 50 miles of altitude (Virgin Galactic)

Kármán Line

Branson has high hopes of making commercial space travel possible with his project in the near future. Virgin Galactic has chosen a technique where launches are made from a mother ship and thus made spaceflight simpler than the traditional rockets that leave the surface.

Despite this, the project suffered a huge setback when the first SpaceshipTwo, named VSS Enterprise, crashed in 2014. Now, VSS Unity, its successor, looks set for ever-growing flights.

However, outer space is not a clear boundary. The end of the atmosphere has different approaches and altitudes. For NASA, exceeding 50 miles means reaching the space, which is recognized by the agency with a special insignia – the FAA also considered that the flight hit the space and will give “wings” to the two pilots. But there are theories that point out that the boundary between the atmosphere and outer space starts at 67 miles (100 km), the so-called Kármán Line.

Outer space or not, at 50 miles altitude the occupants of a spacecraft feel the absence of gravity and can see the Earth’s curvature, an experience similar to that of the X-15 rocket aircraft crew in the 60s in their risks suborbital flights.

But Richard Branson wants more: SpaceShipTwo should reach a day 68 miles high (110 km). “Ever since I watched the moon landings as a child I have looked up to the skies with wonder,” said the British entrepreneur after the historic flight.

The SpaceShipTwo flight, however, is far from where the ISS, the international space station orbits, about 250 miles (400 km). For future passengers of Virgin Galactic certainly these technical details will not spoil the pleasure of reaching so far.

See also: Largest airplane in the world, Stratolaunch performs first test engines