British billionaire Richard Branson’s Virgin Orbit space venture notched another milestone over the Veterans Day weekend: the first high-speed taxi test of its modified Boeing 747 mothership with a LauncherOne rocket tucked beneath its wing.

In a tweet posted today, Virgin Orbit said the Nov. 11 ground test revved up the plane, nicknamed Cosmic Girl, to a speed beyond 110 knots (125 mph) on a runway in Victorville, Calif. That’s fast enough to simulate an aborted takeoff.

“We also used the day as an opportunity to load real flight software onto LauncherOne for the first time,” the company said.

Branson signaled his approval in a follow-up tweet. “Congratulations to all the team on more exciting progress,” he wrote.

Zoom, zoom, zoom, #LauncherOne was on the move again — this time for our very first high-speed taxi test. Not only did we ramp all the way up to more than 110 knots, we also used the day as an opportunity to load real flight software onto #LauncherOne for the first time. pic.twitter.com/sAEtmWLCbu — Virgin Orbit (@Virgin_Orbit) November 13, 2018

Virgin Orbit is taking a step-by-step approach to testing the LauncherOne air-launch system, which relies on the 747 serving as a flying launch pad. Cosmic Girl is designed to carry a two-stage rocket up to an altitude of about 35,000 feet, then drop the rocket from its carrier pylon.

Seconds after release, LauncherOne would fire up its engines to send payloads weighing up to 500 kilograms (1,100 pounds) into low Earth orbit.

The test run serves as another hint that captive-carry tests are near, to be followed by drop tests. If everything goes right, the first launch could take place before the end of the year.

Virgin Orbit is using the air-launch approach because it allows for payloads to be sent into a wide variety of orbital inclinations, potentially with less than a day of pre-launch preparation. Virtually any airport big enough to host a 747 can host Cosmic Girl, which adds to the system’s rapid-response capability.

Future customers include OneWeb, which is working on a constellation of satellites for global internet access; and Seattle-based Spaceflight, which handles the logistics for small-satellite launches.

For what it’s worth, last weekend’s tests tickled Will Pomerantz, vice president of special projects at Virgin Orbit — and a few of his Twitter followers: