While the Stratolaunch has the biggest wingspan, the six-engine Antonov An-225 cargo jet -- which was originally designed to carry a Soviet version of the space shuttle -- is longer. Stratolaunch is 238 feet long while the length of the An-225 is about 275 feet.
Allen, owner of the NBA's Portland Trail Blazers and the NFL's Seattle Seahawks, has written about his desire to see more use of low Earth orbit without breaking the bank.
"With aircraft-like operations, our reusable launch platform will significantly reduce the long wait times traditionally experienced between the construction of a satellite and the opportunity to launch it into space," he wrote last year.
This article originally appeared at: http://www.cnn.com/2017/05/31/us/worlds-largest-airplane-rolled-out-paul-allen/.