The world's largest airplane, built by the late Paul Allen's company Stratolaunch Systems, makes its first test flight in Mojave, California, U.S. April 13, 2019. 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. REUTERS/Gene Blevins

Heavy black smoke rises from one of the six engines starting, before the first test flight of the world's largest airplane, built by the late Paul Allen's company Stratolaunch Systems, in Mojave, California, U.S. April 13, 2019. 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 a.m. 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. REUTERS/Gene Blevins

The world's largest airplane, built by the late Paul Allen's company Stratolaunch Systems, takes off on its first test flight in Mojave, California, U.S. April 13, 2019. 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." REUTERS/Gene Blevins

The world's largest airplane, built by the late Paul Allen's company Stratolaunch Systems, makes its first test flight in Mojave, California, U.S. April 13, 2019. 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. REUTERS/Gene Blevins

The world's largest airplane, built by the late Paul Allen's company Stratolaunch Systems, lands during its first test flight in Mojave, California, U.S. April 13, 2019. Allen, who co-founded Microsoft with Bill Gates in 1975, announced in 2011 that he had formed the privately funded Stratolaunch. REUTERS/Gene Blevins

The world's largest airplane, built by the late Paul Allen's company Stratolaunch Systems, makes its first test flight in Mojave, California, U.S. April 13, 2019. 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. REUTERS/Gene Blevins