Billionaire Paul Allen's private spaceflight company Stratolaunch has just unveiled the world's biggest airplane: a massive carrier plane with a wingspan longer than an entire football field.

The colossal Stratolaunch carrier plane rolled out of its hangar at the Mojave Air and Space Port in Mojave, California, today (May 31) to undergo fueling tests. It's the first public look at the full craft —which is designed to launch rockets into orbit from the sky — since construction began.

"We're excited to announce that Stratolaunch aircraft has reached a major milestone in its journey toward providing convenient, reliable, and routine access to low-Earth orbit," Stratolaunch Systems Corp. CEO Jean Floyd said in a statement. "This marks the completion of the initial aircraft-construction phase and the beginning of the aircraft ground- and flight-testing phase." [Stratolaunch: The World's Largest Airplane in Pictures]

The massive Stratolaunch Systems carrier plane for aerial rocket launches rolls out of its Mojave Air and Space Port hangar in Mojave, California for the first time on May 31, 2017. The aircraft will launch rockets from high-altitude. (Image credit: Stratolaunch Systems Corp.)

The Stratolaunch carrier plane is designed to launch rockets into orbit from an altitude of 30,000 feet (9,100 meters). Initially, the plane will carry a single Pegasus XL rocket built by Orbital ATK, but the craft will eventually be able to carry up to three of those boosters simultaneously, Floyd said.

Stratolaunch Systems has been quietly designing and building the rocket-toting plane over the last few years.

"Over the past few weeks, we have removed the fabrication infrastructure, including the three-story scaffolding surrounding the aircraft, and rested the aircraft's full weight on its 28 wheels for the first time," Floyd said. "This was a crucial step in preparing the aircraft for ground testing, engine runs, taxi tests and, ultimately, first flight."

A drone's-eye view of the Stratolaunch Systems carrier plane as it rolls out of its Mojave Air and Space Port hangar for the first time. The plane has a wingspan of 385 feet (117 meters), longer than a football field. (Image credit: Stratolaunch Systems Corp.)

Allen founded Stratolaunch Systems in 2011 with the goal of making access to low-Earth orbit "more convenient, reliable and routine," according to the company's tagline. Allen teamed up with Scaled Composites, a Mojave-based aerospace company founded by Burt Rutan, to build the Stratolaunch carrier plane.

Allen bankrolled Scaled Composites' SpaceShipOne space plane, which went on to win the $20 million Ansari X Prize for private reusable crewed spacecraft. Stratolaunch's launch profile resembles that of SpaceShipOne, which was carried to launch altitude by its own mothership, called the WhiteKnight.

A view from the twin tails of the massive Stratolaunch Systems carrier plane for aerial rocket launches. The huge craft rolled out of its Mojave Air and Space Hangar for the first time on May 31, 2017. (Image credit: Stratolaunch Systems Corp.)

Paul Allen's Stratolaunch Systems plans to use a giant carrier aircraft to air-launch rockets to Earth orbit. See how the Stratolaunch spaceflight system will work in this infographic (Image credit: Karl Tate, SPACE.com Contributor)

Another private spaceflight company, Virgin Galactic, founded by billionaire Sir Richard Branson, also derived its launch system from Scaled Composites. Virgin Galactic's SpaceShipTwo space planes will launch passenger flights from the belly of a WhiteKnightTwo carrier plane, which has a wingspan of 140 feet (42 m).

But Stratolaunch dwarfs its WhiteKnightTwo cousin.

The Stratolaunch plane is a twin-boom aircraft with a wingspan of 385 feet (117 m), a length of 238 feet (72 m) and a tail height of 50 feet (15 m). The massive plane weighs 550,000 lbs. (250,000 kilograms) by itself and a mind-boggling 1.3 million lbs. (590,000 kg) when fully loaded with a rocket payload. It takes six Pratt & Whitney PW4056 jet engines to power the monster jet.

"Over the coming weeks and months, we'll be actively conducting ground and flight-line testing at the Mojave Air and Space Port," Floyd said. "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."

Email Tariq Malik at tmalik@space.com or follow him @tariqjmalik and Google+. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.