WASHINGTON — Virgin Orbit completed a captive carry test flight of its LauncherOne system April 12, the final major milestone before the company performs its first orbital launch attempt.

The company’s modified Boeing 747 aircraft, with a LauncherOne rocket attached to its left wing, took off from the Mojave Air and Space Port in California at 2:23 p.m. Eastern. The plan flew out over the Pacific Ocean south of Santa Barbara to simulate a launch before returning back to Mojave, with the rocket still attached, about two hours later.

Virgin Orbit had performed captive carry test flights in the past, but this was the first with a flight version of LauncherOne, filled with RP-1 fuel and liquid nitrogen, attached. During the flight, the plane tested the launch release maneuver, where the plane pulls up sharply after releasing the rocket.

In an April 10 statement, Virgin Orbit described then-upcoming flight as a “a complete, end-to-end launch rehearsal” of the aircraft and ground operations, with the exception of using liquid nitrogen, a safer alternative to the liquid oxygen propellant used for LauncherOne. That test, the company said, was also “the last major step prior to our Launch Demo,” or first orbital launch attempt.

Virgin Orbit had planned to carry out the captive carry flight earlier this year, but was delayed in part by the coronavirus pandemic. While among the many space companies considered “essential” by government agencies and thus allowed to remain open, Virgin Orbit sent its staff home with pay for a week last month both to allow them to deal with the dislocations caused by the pandemic as well as to adjust its procedures to allow for on-site operations to continue safely.

That work, Virgin Orbit said in the earlier statement, included reconfiguring its mission control center and rewriting procedures on the shop floor to comply with recommended physical distancing. It is also more frequently cleaning workspaces and increasing use of personal protective equipment. Even with those changes, the company estimates that up to 90% of its employees are still working remotely.

The captive carry test is the last major test before the company’s first launch attempt. “Of course, we’ll first pore over the data from this captive carry flight, and we’ll run through a few last rehearsals, giving the team a few additional chances to practice their jobs with our new COVID-19 procedures in place,” the company stated. “But the Launch Demo will be squarely in our sights.”

Virgin Orbit didn’t state exactly how long it would be before that orbital launch attempt could take place. Previously, company officials estimated they would be ready for the launch as soon as a couple weeks after the captive carry test flight.