Stratolaunch, World’s Largest Airplane by Wingspan, Takes Its First Flight

Its wingspan is longer than a football field. The tail is 50 feet from the ground. It was made by reassembling parts from two used Boeing jetliners.

On Saturday, the world’s largest airplane took flight for the first time.

The twin-fuselage plane, called the Stratolaunch, flew for about two and a half hours over the Mojave Desert in Southern California, reaching a speed of 189 miles per hour and an altitude of 17,000 feet in its maiden voyage, the Stratolaunch team said.

“The flight itself was smooth, which is exactly what you want the first flight to be,” Evan Thomas, a test pilot with Scaled Composites who flew the Stratolaunch, said at a news briefing. “And for the most part, the airplane flew as predicted, which is again exactly what we want.”

The vessel, the largest plane by wingspan, is designed to carry rockets to blast commercial satellites into space. The company is betting that doing so would be more efficient than launching them from the ground, which is an approach of several other space-minded companies.

Paul G. Allen, a founder of Microsoft, funded the project and announced plans for Stratolaunch in 2011. Mr. Allen died in October, prompting questions about the initiative’s future. The company declined to say how much the project cost.

In August, Stratolaunch said it was developing a “family of launch vehicles” that could be deployed from the plane to carry satellites. But in January the company scaled back those efforts.

There have been concerns about how Stratolaunch’s business will work once it takes on customers, with some questioning whether a trend toward smaller satellites would dampen demand for such a large plane.

Even so, the flight on Saturday was billed as a milestone and an engineering marvel.

“All of you’ve been very patient and very tolerant over the years waiting for us to get this big bird off the ground, and we finally did it,” Jean Floyd, chief executive of Stratolaunch, said at the briefing.

The team on Saturday checked the plane’s handling, and tested rolls and yaws.

Mr. Thomas said there were a “few little things that were off nominal” but the company did not immediately specify what those were.

“The airplane felt really nice on the touchdown, gear felt good,” Mr. Thomas said. “We had a couple of corrections to line up in the slowdown and ended up rolling to a stop pretty much where we wanted to coming off the runway.

“So it was overall fantastic.”

Stratolaunch said that by launching rockets from the air, it can “circumvent bad weather, air traffic and other variables that cause delays with traditional ground launches.”

Executives have also said the plane can easily move to areas that are better suited for launching satellites into certain orbits, although it needs a landing strip that can handle its great size.