Destination Moonbase-Alpha.

After an atomic explosion blasts the Moon out of Earth orbit, Moonbase Alpha drifts in space, with 300 people on board. When a rescue team from Earth arrives in a faster-than-light space ship, everyone is overjoyed that they can now return to Earth. But Moonbase Commander John Koenig, having undergone an experimental brain soothing process after receiving a concussion in a crash on the Lunar surface, sees not friends from Earth but gruesome monsters which have telepathically caused all others on Alpha to see an illusion of an Earth party. The aliens are desperate for radiation and plan to manipulate the Alphans into detonating nuclear waste on the Lunar surface, reducing the Moon and everyone on it to dust. Koenig must expose this conspiracy to save his people. Compiled from the two part episode The Bringers Of Wonder from the TV series Space: 1999's second series.