The full-scale prototype soared more than 10 kilometres after lift-off from the southern tip of Texas on Wednesday.

It descended horizontally over the Gulf of Mexico and then flipped upright just in time to land.

This time, the shiny bullet-shaped rocketship remained intact, prompting commentator John Insprucker to declare, "third time's a charm as the saying goes".

"We've had a successful soft touchdown on the landing pad," he added.

SpaceX founder Elon Musk plans to use Starships to send people to the moon and Mars.

The last two prototypes reached a similarly high altitude in December and February but slammed into the ground at Boca Chica, Texas, and exploded.

There's another test flight planned soon.

Each of these last three test flights lasted six-and-a-half minutes.

Australian Associated Press