This major test will be the company's final before its first launch demonstration flight, with the flight apparently going off without a hitch.

Virgin Orbit hopes to one day offer a flexible and responsive launch service for those looking to place small satellites into orbit. Rather than having rockets lift off vertically from a pad, Virgin Orbit aims to use a 747 that has been modified to carry a rocket beneath its wing, which then launches toward space from midair and takes a payload along for the ride. The plane then lands on the airstrip like a conventional aircraft, ready to go again.

It has carried out a number of test flights in recent years, showing off its so-called Cosmic Girl mothership in action. In late 2018 November, it started taking its LauncherOne rocket along for the ride and then in July of last year, it dropped the rocket for the first time to make sure the release mechanisms were in working order.

Today's captive carry test is different to those that have gone before it, however. In previous tests, the fuel tanks were filled with water to simulate the weight and balance of the real thing. This time around, they were filled with liquid nitrogen which was cryogenically cooled to be around 300 °F (185 °C) colder than the water, which interacts differently with the onboard hardware systems and calls for special handling by Virgin Orbit workers.