Microsoft [MSFT] co-founder Paul G. Allen’s Stratolaunch Systems brought out its massive low Earth orbit (LEO) air-launch platform from its hangar for the first time on May 31 and announced it is ready for ground and flightline testing.

Stratolaunch, founded in 2011, rolled out the aircraft, with its 385-foot wingspan and six Boeing [BA] 747 engines, and which aims to provide convenient, reliable access to LEO flights. The showcase on May 31 marked the completion of the initial aircraft construction phase.

The rocket-launching aircraft is the largest all-composite plane ever built, and has a payload capacity of over 500,000-pounds and an operational range of around 2,000 nautical miles. Stratolaunch touts its goal of reusability and unique air-launch capabilities in its aim towards eventually taking an airport-style launch approach to LEO flights.

The roll-out on May 31 coincided with the removal of the aircraft’s fabrication infrastructure and the first time the full weight of plane was tested on its 28 wheels.

Stratolaunch will now move into ground testing, engine runs, taxi tests, before eventually attempting its first test flight.

“This is a first-of-its-kind aircraft, so we’re going to be diligent throughout testing and continue to prioritize the safety of our pilots, crew and staff. Stratolaunch is on track to perform its first launch demonstration as early as 2019,” CEO Jean Floyd said in a statement.

In Oct. 2016, Stratolaunch announced a multi-year partnership with aerospace manufacturer Orbital ATK [OA] to produce Pegasus XL air-launch vehicles to be used with Stratolaunch aircraft. This will give potential customers the ability to launch small satellites weighing up to 1,000 lbs into low earth Orbit.

Stratolaunch aims to be fully operational by 2019, while construction and testing continues to take place at the Mojave Air & Space Port in Mojave, Calif.