He joined the National Space Development Agency of Japan (NASDA) in 1992 and worked in the development of the H-II launch vehicle for two years. From 1994 to 1999, he was as an astronaut support engineer for the NASDA Astronaut Office, supporting the development of the astronaut training program and supported astronaut Koichi Wakata during Wakata's training and mission on STS-72.
In February 1999 Hoshide was selected by NASDA (now JAXA) as one of three Japanese astronaut candidates for the International Space Station (ISS). He started the ISS Astronaut Basic Training program in April 1999 and was certified as an astronaut in January 2001. Since April 2001, he has participated in ISS Advanced Training, as well as supporting the development of the hardware and operation of the Japanese Experiment Module Kibō and the H-II Transfer Vehicle (HTV).