More than 13,000 satellites operate in low Earth orbit (LEO), and concern has grown that nuclear weapons could be used in space to target them. Beyond the initial X-ray burst, electrons released by radioactive fission products can become trapped in Earth's magnetic field, repeatedly exposing satellites as an artificial radiation belt. Here we couple prompt radiation, electron trapping and belt evolution to satellite failures, collisions and atmospheric drag. For a 1-Mt detonation at 500km over the South Atlantic, repeated belt exposure disables approximately 98% of modeled satellites within one week in our central case. Tripling the assumed radiation tolerance delays widespread failure by only days: approximately 97% are still disabled within two weeks. The loss of maneuverability sharply increases collision risk, with approximately 20 collisions expected within two years. Drag removes many disabled spacecraft from lower altitudes, but replacement satellites could remain exposed to radiation and debris for years. These findings show how a single detonation could devastate orbital infrastructure and support efforts to prevent the deployment and use of nuclear weapons in space.