He appears periodically to people on Earth in normal time. Earth is ravaged by war and culture is reset. People forget about the true nature of his origin, see him as a manifestation of a god at first, then slowly realize he is a leftover from the civilisation that destroyed itself with mighty weapons. The man in the spacesuit is trapped and his oxygen supply is depleting, yet his time is drastically slower than that of Earth people, who witness the dial of his oxygen supply going down into the red zone over the course of many hundreds of years.
I read this when I was younger (in the 1980s) and it haunts me that I have not been able to find the name and author of this story.