Built in Europe, the Solar and Heliospheric Observatory (SOHO) was launched on December 2nd, 1995 and, despite being planned as a two year mission, it is still going, with the latest predicted end date being in 2020. It is a joint project between ESA and NASA, built by Matra Marco I Aerospace, and designed to provide data to help predict solar weather, and answer questions about the solar interior, solar wind, and why the corona is so hellishly hot. The mission has been a great success, providing significant insights into such areas as the structure of sunspots, the flow of gases inside the Sun, and the dynamics of the solar wind.
In addition to all this, SOHO has still found time to become history’s greatest ever discoverer of comets, with the total ticking over to an astonishing 3000 on September 13th 2015. Comet number 3000 was spotted by Thai astronomer Worachate Boonplod, part of an amateur army of spotters who betwen them have been responsible for the majority of SOHO discoveries.
The Broad Band X-ray Telescope (BBXRT) was launched today (1990) on board shuttle Columbia flight STS-35. It formed part of the partly-successful “ASTRO-1” payload of four instruments.
The mission was somewhat shorter than the previously-mentioned SOHO, as the telescope was attached to the shuttle, and had to go wherever it went (back to Earth).