Here's the story of how Japan's H3 rocket lost its cargo and just kept going

Summary

If you’re in the space business long enough, you learn there are numerous ways a rocket can fail. I’ve written my share of stories about misbehaving rockets and the extensive investigations that usually—but not always—reveal what went wrong. But I never expected to write this story. Maybe this was a failure of my own imagination. I’m used to writing about engine malfunctions, staging issues, guidance glitches, or structural failures. Last April, Ars reported on the bizarre failure of Firefly Aerospace’s commercial Alpha rocket. Japan’s H3 rocket found a new way to fail last month, apparently eluding the imaginations of its own designers and engineers. The H3 is a relatively new vehicle, with last month’s launch marking the eighth flight of Japan’s flagship rocket. The launcher falls on the medium-to-heavy section of the lift spectrum. The eighth H3 rocket lifted off from Tanegashima Island in southern Japan on December 22, local time, carrying a roughly five-ton navigation satellite into space. The rocket was supposed to place the Michibiki 5 satellite into an orbit ranging more than 20,000 miles above the Earth. Everything was going well until the H3 jettisoned its payload fairing, the two-piece clamshell covering the satellite during launch, nearly four minutes into the flight. Officials from the Japan Aerospace Exploration Agency (JAXA) are starting to get a handle on what happened. Agency officials briefed the government ministry overseeing Japan’s space activities last week, and the presentation (in Japanese) was posted on a government website. The presentation is rich in information, with illustrations, a fault tree analysis, and a graph of in-flight measurements from sensors on the H3 rocket. It offers a treasure trove of detail and data most launch providers decline to release publicly after a rocket malfunction. Japan’s eighth H3 rocket climbs away from Tanegashima Space Center on December 22, 2025, with the Michibiki 5 navigation satellite. Credit: JAXA Ja...