OSO stands for Orbiting Solar Observatory, and OSO-7 was the seventh of these. In all there was 8 of them, and they were launched between 1962 and 1975.

Although Skylab is more well-known than the OSO satellites, the OSO satellites discovered many new things (including CMEs) and also some of the technology used on Skylab was tested on the OSOs.

Image courtesy of NASA.