Elon Musk’s Starship makes a test flight without exploding

“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.

The Starship upper stage is partly coated with hexagonal tiles which act as a heat shield. These cover the side of the vehicle which faces Earth during re-entry, in order to protect it from the heat of friction with the atmosphere. They are similar to the tiles previously used on the Space Shuttle. Some spacecraft have “ablative” heat shields which are partly burned away during re-entry and are not meant to be reused. But SpaceX wants the Starship system to be completely reusable, without the need for months of refurbishment between flights. So the performance of the tiles is crucial. During the test flight in March, the Starship began to roll uncontrollably, which meant the tiles were not facing in the right direction, and the vehicle eventually broke up. But even when the ship is correctly oriented, the gaps around the flaps (which must be able to move) could still present a weakness in the heat shield. This was what Mr Musk was anxious to test.

The fourth test flight blasted off from SpaceX’s base near Boca Chica in Texas at 7.50am local time. One of the Super Heavy’s 33 engines failed to light, but the first phase of the flight was otherwise unremarkable. The Starship separated from the booster three minutes after launch at an altitude of 73km and continued under its own power; the booster performed a series of landing burns and made a “soft splashdown”—a gentle, vertical landing on the sea—in the Gulf of Mexico before slipping beneath the waves. This was a practice run for future landings at Boca Chica, where the plan is for the booster to fly back to its launch-pad and be grabbed by two giant arms, known as “chopsticks”, as it hovers. (In the test flight in March, the booster exploded while attempting its landing at sea.)

Starship’s upper stage, meanwhile, left the atmosphere and travelled halfway around the world. Around 45 minutes into the flight, live video from cameras on the Starship showed orange plasma around the vehicle as it began re-entry. The plasma glow gradually became brighter and more intense as the Starship passed through the point of peak heating. All eyes were then focused on a view of one of the forward flaps, where plasma suddenly began to eat away at the flap’s edge. A crowd of employees at SpaceX’s headquarters could be heard crying out in alarm as pieces of the flap started to break off. But their cries turned to cheers as the ship continued its descent, despite its damaged flap, performed a “flip” manoeuvre and made its own soft splashdown in the Indian Ocean. The heroic flap prompted an immediate flood of laudatory internet memes.

“Despite loss of many tiles and a damaged flap, Starship made it all the way to a soft landing in the ocean!” Mr Musk posted on X. So the answer to the question he had posed the day before is that the seal worked just well enough to allow the Starship to re-enter the atmosphere—but the thermal protection around the flaps evidently needs further work if SpaceX is to achieve its goal of full reusability. “We will have this nailed for the next flight,” Mr Musk insisted.

SpaceX will spend the coming weeks analysing readings from both booster and Starship in preparation for that flight. They should contain plenty of useful information. In order to test the heat shield’s performance, two tiles were deliberately omitted from the heat shield, and one was made thinner than usual. “The payload for this test was the data,” the company posted, also on X. “Starship delivered.” Both parts of Starship ended up at the bottom of the sea. But the giant rocket has taken another step towards being able to carry people to the Moon, Mars and beyond. ■

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