Tristan Buckmaster was on the path toward an important proof when one of the A.I. giants used its staggering resources to get there first.

Andy Green, a 64-year-old retired Royal Air Force pilot from Britain, was already the only person to break the sound barrier on land. “The ground comes at you very, very quickly,” he said.

Elon Musk’s rocket company said it would sell more than 555 million shares at $135 each in its blockbuster initial public offering, which is set to begin trading on Friday.