The 1967 Outer Space Treaty prohibits placing nuclear weapons in orbit, but there is currently no reliable way to verify whether any are actually in space. To address this gap, MIT associate professor Areg Danagoulian has proposed a satellite-mounted sensor that could detect the neutrons emitted by radioactive material as a suspect satellite passes through the Van Allen radiation belts. The concept could help identify nuclear weapons in orbit, but only if a specific satellite has already been singled.