Earlier this month, a curved aluminum skeleton 40 feet long sat waiting in Hermeus’ cavernous Atlanta factory. It was the prototype of a drone called Quarterhorse. It will never fly. Instead, it’s scheduled for ground-testing starting in September. Hermeus CEO AJ Piplica and his cofounders believe it’s the first step on a long road to an audacious goal: building a plane capable of carrying 20 passengers at hypersonic speed — five times faster than sound, or 3,850 miles per hour.

Imagine New York to Paris in 90 minutes. Quite an upgrade from the seven-and-a-half hours of a commercial flight today.

It’s been 20 years since the last flight of Concorde, the groundbreaking but money-losing supersonic jetliner. So far, none of a parade of startups that have tried to bring back supersonic travel have left the ground. Piplica acknowledges that Hermeus is taking on even harder technical challenges in building an airliner that can fly for long periods of time in the intense heat and weird dynamics created the farther you climb above the speed of sound. But he says that’s not the biggest problem. “The business challenges are actually the real hard ones,” Piplica, 35, tells Forbes. “You’re not just going to raise billions of dollars to develop a passenger aircraft.”

Piplica’s solution: to prove the technology largely on the Pentagon’s dime by developing smaller hypersonic drones, taking advantage of Washington’s urgency to catch up to Russia and China in fielding maneuverable hypersonic missiles.

Quarterhorse is intended to serve as a reusable testbed to subject materials and equipment to high-speed conditions. Hermeus won a $30 million contract from the U.S. Air Force that will go toward building and flying three versions of the aircraft. First flight is slated for 2024, and Piplica says he expects the total development cost to be under $100 million.

A larger second drone, Darkhorse, which Hermeus hopes to start flight-testing in 2026, is also planned to be used as a test vehicle, as well as for long-range surveillance and strike.

If it works out, by the time Hermeus gets to building Halcyon, its planned airliner, Piplica says they’ll have successively built six to ten prototypes of Quarterhorse and Darkhorse and found solutions to many of the technical unknowns of high-speed flight. After all, Piplica says, humans have only about 30 minutes of experience over Mach 4 with so-called air-breathing aircraft, which use the oxygen around them for fuel combustion instead of carrying it onboard as rockets do, leaving less room for payload like passengers. When all the testing is done, Piplica expects to have a fleet of hypersonic drones earning solid revenue performing Defense Department missions.