The Psi-moon was the result of the most advanced and experimental terraforming technology of the Space Corps. An artificial S3 moon in Deep Space, the Psi-moon could "tune into the psyche" of any human or hologram astro that landed on it, rapidly re-configuring and landscaping itself accordingly to their mental state. This could be a very dangerous place to be for the mentally unbalanced and deranged, such as Arnold Judas Rimmer, the Psi-moon's last visitor.