Founded by the late Microsoft billionaire Paul Allen in 2011, Stratolaunch Systems Corporation finally executed the first successful test flight of "Roc," the world's largest aircraft, on April 13 in California.

Roc is a carrier aircraft designed to carry and launch small rockets carrying satellites into Low Earth Orbit (LEO) from the stratosphere. It took off at 9:58 a.m. EDT (1358 GMT) from the Mojave Air and Space Port, reaching 4,600 meters (15,000 ft.) and 305km/h in a first flight that lasted 2 hours and 29 minutes.

Crowds cheered as the ungainly Roc, which will pioneer the air-launch industry, lifted-off from the desert airport runway.

"WOW. First flight of the worlds largest airplane. History is made. @Stratolaunch @NASASpaceflight #stratolaunch," tweeted Jack Beyer, an aerospace photographer who was onsite.

Roc reached a peak altitude of 5,180 meters and a top speed of 304 km/h, said Stratolaunch in a statement. It was flown by Evan Thomas, a former U.S. Air Force F-16 fighter pilot, from one of the enormous plane's two cockpits.

The maiden flight of Paul Allen's "baby" with two connected fuselages allowed pilots to evaluate Roc's performance and handling. Roc is basically a giant flying launch pad that will hurtle satellites into LEO. It offers the U.S. military, private companies, and NASA a more economical way to get into space compared to vastly more expensive ground-launch systems.

"We all know Paul would have been proud to witness today's historic achievement," said Allen's sister, Jody Allen, chair of Vulcan Inc. and trustee of the Paul G. Allen Trust. "The aircraft is a remarkable engineering achievement, and we congratulate everyone involved."

Stratolaunch CEO Jean Floyd was ecstatic.

"We finally did it," said Floyd. "It was an emotional moment to watch this bird take flight."

"I had imagined this moment for years, but I had never imagined it without Paul standing next to me," he said, adding that he whispered a private "Thank You" to Allen as the plane took to the air.

"What a fantastic first flight," exclaimed Floyd. "Today's flight furthers our mission to provide a flexible alternative to ground-launched systems. We are incredibly proud of the Stratolaunch team, today's flight crew, our partners at Northrup Grumman's Scaled Composites and the Mojave Air and Space Port."

Allen died in October 2018 at age 65 from complications related to non-Hodgkin's lymphoma.

From wingtip-to-wingtip, Roc measures 117 meters (385 feet), which is wider than any airplane on the planet. From nose to tail, it's 73 meters (238 feet) long. It weighs 227,000 kg (500,000 lbs.) Roc is so massive it has two cockpits, one in each fuselage. Only one cockpit is used to fly the plane, however.

Each of the two fuselages is 72 meters long and is supported by 12 main landing gear wheels and two nose gear wheels for a total of 28 wheels.

The power plant of this rocket launching monster consists of six thrust-range jet engines sourced from two used 747-400s. It generates from 205 kN to 296 kN (46,000 to 66,500 pound-force) of thrust.

"For the most part, the plane flew as predicted," said Thomas. "It was overall fantastic. I honestly could not have hoped for more on a first flight, especially of an airplane of this complexity and this uniqueness."