Hear the story of the astro-chimps

However, their "retirement" has caused controversy among animal welfare activists who want officials to rule out any chance that the chimps will be used for experiments.

The air force has invited bids for around 100 of the animals. These include astro-chimps like the one which orbited the earth in 1961 to prove that space flight would be safe for humans, and his descendants.

The air force brought the original chimp colony from Africa in the early stages of the space programme. Since then, they have been credited with playing an important role in experiments on space travel.

Cage space

The chimps, who live in cages, have been leased by the airforce to a bio-medical research lab in the desert town of Alamagordo, New Mexico.

Animal welfare activists have objected to them having anything to do with testing vaccines or other medical research experiments. Instead, they want them to be "retired" to a chimp sanctuary.

One supporter said: "They worked for a living. They are armed forces veterans. We want to give them their pensions."