A pint-sized Japanese robot that became the first android to converse with an astronaut in space has returned to Earth after 18 months in orbit, project organisers said Thursday.

"Kirobo" -- roughly the size of a chihuahua -- hitched a ride back from the International Space Station (ISS) on a cargo supply spacecraft that splashed down in the Pacific Ocean, sponsors including Toyota Motor and advertising firm Dentsu said.

Kirobo, which left Earth in August 2013, was programmed to communicate in Japanese and keep a record of its conversations with Koichi Wakata, the first Japanese astronaut to command the ISS.

The robot was part of a study aimed at learning how a non-human companion can provide emotional support for people isolated over long periods.

Millions of Japanese schoolchildren were captivated by the adventures of a creation that showcased Japan's drive to combine cutting-edge technology and its obsession with all things cute.