Cosmic Girl takes off from a conventional runway and carries the rocket up to an altitude of about 35,000 feet.

Once it's reached altitude, Cosmic Girl pitches up to about 25 degrees, and releases the rocket.

The rocket fires its single main-stage engine, a 73,500 lb./f. rocket engine called Newton Three. Newton Three fires for about 3 minutes, then separates.

The single upper-stage 5,000 lb./f. rocket engine called Newton Four fires multiple times—for up to 6 minutes total burn time—to place the satellite(s) in orbit.

Both rocket stages are safely de-orbited, and Cosmic Girl returns to a pre-determined airport.

Richard Branson's Blog Post: Virgin Orbit's Launcher One Meets Cosmic Girl 747

Virgin Orbit website