COLORADO SPRINGS, Colo. — Microsoft co-founder Paul Allen’s Stratolaunch space company says it’s on track to conduct the first test flight of its mammoth airplane this summer, and use it to send rockets into orbit as early as 2020.

The status check came today during a background briefing here at the 34th Space Symposium, conducted under background-only conditions that precluded quoting sources by name.

Stratolaunch was founded by Allen in 2011, with the goal of building a giant plane that could be used as a platform for sending payloads into space.

Scaled Composites built the plane for Stratolaunch inside a giant hangar at the Mojave Air and Space Port in California. Its wingspan is the widest in the world, measuring 385 feet. That’s almost twice as wide as a Boeing 747’s wings.

Last December, the plane went through its first runway taxi test at a speed of up to 15 knots (17 mph). In February, the plane returned to Mojave’s runway for a highly successful taxi test that revved the plane up to 40 knots (46 mph).

Now Stratolaunch has three more ground-based taxi tests on its agenda, at speeds stepping up to 70 knots (81 mph), 85 knots (98 mph) and 120 knots (138 mph). That last figure roughly matches the speed that the plane would need for takeoff.

If all goes well, that would open the way for a “first flight” during the summer months. A series of flight tests would have to be conducted as part of what’s typically an 18- to 24-month process for gaining airworthiness certification from the Federal Aviation Administration. Only then will Stratolaunch be in a position to start midflight rocket launches.

That timeline suggests that Stratolaunch’s “first launch” would take place no earlier than 2020.

The Stratolaunch flight profile calls for carrying up to 550,000 pounds’ worth of rockets and payloads beneath the center of the plane’s wings, between the two fuselages. When the plane reaches an altitude in the neighborhood of 35,000 feet, the rockets would be dropped from the mothership, fire up their engines and press onward to orbit.

Such a system would allow for a launch into any orbital inclination, from anyplace within range of a suitable runway. It’s a super-sized version of the air-launch concept used for the SpaceShipOne rocket plane project that Allen bankrolled more than a decade ago, as well as for Virgin Galactic’s SpaceShipTwo and Virgin Orbit’s LauncherOne systems

Eventually, the plane could accommodate up to three rockets for separate launches during a single sortie. But for the first launches, the plane will carry only one 50,000-pound Orbital ATK Pegasus XL rocket. That’s meant to simplify the process for getting regulatory clearance for the initial launches, because the Pegasus is already being air-launched in this way from Orbital ATK’s modified Lockheed L-1011 carrier plane.

Stratolaunch says it hasn’t yet signed up customers, but it intends to put commercial payloads on its first launches — perhaps at a discounted rate. (Don’t expect to see another sports car put into space.)

What sorts of payloads could Stratolaunch launch? The likeliest prospects are small satellites for commercial, governmental or military applications. Allen has said he’s particularly interested in applications that address his own interests — which include wildlife conservation, climate change and countering illegal fishing.

The company is also working on a design for a reusable space plane that could be air-launched to deploy satellites in orbit, or eventually carry people into space. That project, known as “Black Ice,” is probably at least five years away from taking flight.

Eventually, Allen and his Stratolaunch team envision creating a launch system that makes getting into space as easy as scheduling a trip from Los Angeles to Washington, D.C., on an ordinary airplane — that is, an airplane that doesn’t have six engines, two fuselages and a wing that’s wider than a football field.