“ONE OF THE key questions is—does that seal work? We think it will work, but it may not work,” said Elon Musk, the boss of SpaceX, on June 5th, as his company’s Starship rocket was being prepared for its fourth test flight the following day. He was referring to one particular component of the rocket: the thermal protection around the steering flaps used during re-entry from orbit. Mr Musk was talking to Tim Dodd, a YouTuber known as Everyday Astronaut. In the event, the test flight went well: the launch went as planned and there was no “rapid unscheduled disassembly” (ie, catastrophic explosion). But the focus on the seal around those flaps proved to be strikingly prescient.

Starship is the world’s largest rocket. It consists of two parts: the Super Heavy booster stage, a behemoth 71 metres tall with 33 engines, and the 50-metre Starship upper stage. On Starship’s first two test flights it failed to reach orbit; it managed on the third, in March, but then broke apart while re-entering the atmosphere. SpaceX’s primary goal, for the uncrewed test flight on June 6th, was successful atmospheric re-entry of the upper stage.