Spacecraft has a great post on the Solar Maximum Mission. The satellite was launched in 1980 to study the effects of increased solar activity that occurs every 11 years (the “Solar Maximum“). There were serious issues with the hardware, and it took a shuttle servicing mission in 1984 to set things right. Luckily, the SMM had been designed using a modular architecture, which allowed relatively simple replacement of faulty components.
I remember reading about the problems with the SMM as a kid and following the story as it unfolded, mostly in the pages of Astronomy magazine. Check out the link-rich post. Good stuff.