Tadashi Hoshika

An employee at JAXA who initially wanted to become an astronaut but wasn't lucky enough. He inspired Mutta and Hibito when they were young and was a part of the JAXA team who conducted the series of astronaut recruitment tests. Hoshika personally informed Nanba Mutta about his result after the last test in the program.

(Source: Uchuu Kyoudai Wikia)