A leaky valve reportedly allowed propellant to enter high-pressure helium tubes some 100 milliseconds before the spacecraft’s thrusters were due to ignite. A slug of liquid oxidizer—known as nitrogen tetroxide (NTO)—wound up in a high-pressure system, resulting in a structural failure and, ultimately, an explosion, according to SpaceX. In partnership with NASA, the Federal Aviation Administration (FAA), and the National Transportation Safety Board (NTSB), the aerospace manufacturer led an investigation into the “anomaly.” It helps that the blast happened on land, leaving behind debris and intact parts that are easier to examine than, say, components lost in outer space or scattered across an ocean. The ruined rocket was a test version of SpaceX’s Crew Dragon—a capsule being built for NASA to take astronauts to and from the International Space Station. This particular module was the first Crew Dragon launched into space: In March, the unoccupied vehicle successfully docked with the ISS, before splashing down in the Atlantic Ocean in a flawless test mission. A month and a half later, the spacecraft detonated, sending clouds of orange gas into the Florida sky. “It is worth noting t...