Seattle billionaire philanthropist Paul Allen’s death comes just as his Stratolaunch space venture is counting down to the first flight of the world’s biggest airplane — and lifting the veil on a wide range of space applications.

Now it’s up to the Stratolaunch team to make good on the high-flyingest idea from the self-described “Idea Man,” who succumbed to non-Hodgkin’s lymphoma at the age of 65.

Heading that team is President and CEO Jean Floyd, who spent decades as a manager and executive at Orbital Sciences Corp. (now part of Northrop Grumman) before joining the venture in 2015.

Like many of the other executives in Allen’s wide-ranging operation, Floyd confined his comments about his boss’ death to a Twitter tribute: “We deeply respect and admire Mr. Allen’s vision. His legacy will be honored,” Floyd wrote.

Just a week earlier, Floyd was tweeting about a happier subject: a revved-up series of taxi tests that sent Stratolaunch’s 385-foot-wide, twin-fuselage plane down Mojave’s runway at speeds as fast as 80 mph. Additional rounds of taxi tests are expected in the weeks ahead, setting the stage for the maiden flight.

Stratolaunch expects to get the plane certified for air-launch operations after 18 months to two years’ worth of flight tests, .

The concept is a scaled-up version of the SpaceShipOne launch system that won the Ansari X Prize for private spaceflight in 2004, thanks to $28 million in backing from Allen. It calls for the plane to fly up to an altitude of about 30,000 feet, then release a rocket from its underbelly. Seconds after the drop, the rocket lights up its engine and ascends into space.

“One of the unique things about Stratolaunch is that it doesn’t require a fixed launch pad,” Allen told GeekWire last year. “You can imagine systems that are very flexible for missions where you want to launch satellites at different orbits, from different angles. … Then there’s the fact that just doing an air launch gives you an advantage of probably 30 percent in performance.”

Just in the past couple of months, Stratolaunch’s executives and engineers have revealed the outlines of Allen’s space vision — a grand plan that includes the development of a new type of rocket engine, a whole family of launch vehicles including a crew-carrying space plane, a partnership to create new space outposts, and a hypersonic testbed with obvious military applications.

One of the big mysteries surrounding Stratolaunch has to do with its customers: The venture’s timeline for launches in the early 2020s is similar to the schedule laid out by another billionaire-backed space effort, Amazon founder Jeff Bezos’ Blue Origin venture. But Blue Origin has announced several launch deals, while Stratolaunch hasn’t announced any.

Stratolaunch’s initial target customers may still be in wait-and-see mode, in stealth mode, or in a combination of both modes.

It’s worth noting that the air-launch system’s versatility could address the U.S. national security community’s need for rapid-response launches in the years ahead. That potential synergy came into the spotlight a year ago when Vice President Mike Pence and his entourage visited Stratolaunch’s hangar in Mojave

Just after the visit, Floyd said he and Pence discussed “how NASA and the Department of Defense can utilize small satellites and small launch capabilities for flexible, rapid deployments and stronger resiliency in space.”

“I’m encouraged by the positive response we continue to receive from our public officials,” he said.

As Stratolaunch’s leaders follow through on Allen’s space vision, might they pay special tribute to the venture’s founder? There’s precedent for that.

SpaceShipOne’s designer, Burt Rutan, had some of his mother’s ashes flown aboard the rocket plane during one of its prize-winning flights in 2004, and it’s not hard to imagine that Stratolaunch might do something similar. When Virgin Galactic founder Richard Branson then licensed SpaceShipOne’s technology from Allen for the SpaceShipTwo rocket plane, he named its mothership after his own mother, Eve Branson. It’s not hard to imagine that Stratolaunch might follow the model set by the VMS Eve, and call its giant plane the “MS Paul Allen.”

The biggest tribute may well lie in knowing that Paul Allen blazed the trail for the personal spaceflight era in the 21st century, just as he blazed the trail for the personal computer era at Microsoft in the 1970s. And the biggest tragedy may well be that he passed away just as the new commercial space age was finally coming into its own.

“A lot of our pioneers in the commercial spaceflight industry have arisen just in the last 10 or 15 years,” Eric Stallmer, president of the Commercial Spaceflight Foundation, told GeekWire today. “It’s a setback. It makes you pause a little bit.”

Update for 10:50 a.m. PT Oct. 18: Phil Larson was a space policy adviser in the Obama White House and a spokesman for SpaceX, and now serves as assistant dean and chief of staff at the University of Colorado-Boulder’s College of Engineering and Applied Science. Here’s what he had to say about Stratolaunch’s plans for future flights: