Terra Alpha was an Earth colony planet with a yellow-purplish atmosphere. The human colonists were called "Alphans" and the native Pipe People were driven underground where they eventually took to living in pipes throughout the city. (TV: The Happiness Patrol)
According to the Seventh Doctor, the colony was settled "some centuries" in Ace's future, (PROSE: The Happiness Patrol) at the earliest by 2136. The colony may have sold weapons to the Selachians as they had a "falling out" with the rulers of Terra Alpha and attacked the planet, the rulers unable to stop them. (PROSE: The Murder Game)
By the 24th century, it was ruled by Helen A with her control maintained through the "Happiness Patrol." There were specified tourist zones, a rocket pod zone with scheduled flights, and a waiting zone that moved to different places depending on the time of night. This was in place of a prison, prisons being considered dreadful places. Helen A had built over 1,000 factories that were staffed by drones who came from the flatlands and were forbidden to enter the city.
All those who lived on Terra Alpha had a normal name, followed by a grading letter. Those who weren't from the planet were given "Sigma" as their grading and required badges. "Lift music" music was played throughout the streets and television was available for Helen A's broadcasts.
Wanting a strong world where tears were held back and everyone was happy, Helen A created the Happiness Patrol to enforce her laws that everyone had to be happy. Those who were unhappy were executed, usually by the Kandyman. After it was deposed when Helen A lost her pet Fifi and realised that unhappiness was integral to life, the planet became a free colony. (TV: The Happiness Patrol)