The world's largest aircraft took off over the Mojave Desert in California on Saturday, the first flight for the carbon-composite plane built by Stratolaunch Systems Corp, started by late Microsoft co-founder Paul Allen, as the company enters the lucrative private space market.

The white airplane called Roc, which has a wingspan the length of an American football field and is powered by six engines on a twin fuselage, took to the air shortly before 7 am Pacific time (1400 GMT) and stayed aloft for more than two hours before landing safely back at the Mojave Air and Space Port as a crowd of hundreds of people cheered.

"What a fantastic first flight," Stratolaunch Chief Executive Officer Jean Floyd said in a statement posted to the company's website.

"Today's flight furthers our mission to provide a flexible alternative to ground launched systems, Floyd said. "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."

The plane is designed to drop rockets and other space vehicles weighing up to 500,000 pounds at an altitude of 35,000 feet and has been billed by the company as making satellite deployment as "easy as booking an airline flight."

Saturday's flight, which saw the plane reach a maximum speed of 189 miles per hour and altitudes of 17,000 feet, was meant to test its performance and handling qualities, according to Stratolaunch.

Allen, who co-founded Microsoft with Bill Gates in 1975, announced in 2011 that he had formed the privately funded Stratolaunch.

The company seeks to cash in on higher demand in coming years for vessels that can put satellites in orbit, competing in the United States with other space entrepreneurs and industry stalwarts such as Elon Musk's SpaceX and United Launch Alliance - a partnership between Boeing and Lockheed Martin.

Stratolaunch has said that it intends to launch its first rockets from the Roc in 2020 at the earliest. Allen died in October 2018 while suffering from non-Hodgkins' lymphoma, just months after the plane's development was unveiled.

"We all know Paul would have been proud to witness today's historic achievement," said 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."