On Wednesday morning, a rather unusual plane could be seen flying high over Edwards Air Force Base in Southern California. Unlike the military aircraft endemic to the area, this was a modified Boeing 747 jumbo jet, its bright red tail emblazoned with a single word: VIRGIN. A 70-foot rocket was strapped beneath its left wing, and about 30 minutes after takeoff jet pilot Kelly Latimer released the rocket and sent it careening to the desert floor 35,000 feet below.

Although the rocket was “fully loaded,” as the company put it, its engines never fired—nor were they meant to. Instead, the rocket fell freely to Earth so the company could see how it performed during its first few seconds of freefall. This was the last major test for Virgin Orbit’s air-launch system, which will launch rockets from a gutted jumbo jet, known as Cosmic Girl, to boost small satellites into orbit. It’s a complicated maneuver, but it could significantly reduce the costs of getting to space.

A large fraction of a vertically launched rocket’s mass is fuel, most of which is needed to fight atmospheric drag and Earth’s gravity near the surface. Having a plane carry a rocket to high altitudes can conserve much of that fuel. Unlike rockets, planes don’t require an oxidizer to fly to high altitudes, which also helps cut down on the rocket’s mass and reduces the cost of an orbital launch. Indeed, Virgin estimates that a ride to orbit on its LauncherOne rocket will cost only about $12 million, which is almost pocket change in the space industry.

The advantages of an air-launch system have been known for decades, but only recently has the space industry started to show interest in the concept. The exception is Orbital ATK, which became the first company to use an air-launched rocket to deliver a satellite to orbit, in 1990, and continues to use that system to this day. The last decade has seen a resurgence of interest in the concept, attracting new space companies like Stratolaunch, XCOR, and Generation Orbit, as well as old guard contractors like Boeing and Lockheed Martin. Even SpaceX briefly flirted with the idea of an air-launch system for a modified Falcon 9 rocket before abandoning the project in 2012. But among the new guard, only Virgin has brought its air-launch system to fruition.