Virgin Galactic says the latest glide test of its space tourism rocket plane was a success, nearly reaching the speed of sound high over California.

The spaceship, named Unity, was carried aloft by its mother ship on Thursday and released over the Mojave Desert.

The craft was immediately put into a steep descent and accelerated to Mach 0.9 to test stability and control under forces approaching what it will endure when its rocket is fired for suborbital flights into the lower fringes of space.

It was the seventh glide flight for Unity.

Virgin Galactic did not indicate whether the program is ready to move on to rocket-powered test flights.