First on-orbit satellite maintenance

The first on-orbit repair of a failed satellite took place during Space Shuttle mission STS-41-C between 8 and 11 April 1984. The mission saw the Space Shuttle Challenger rendezvous with the Solar Maximum Mission (SMM), a research satellite designed to monitor solar activity, which had suffered a loss of attitude control in November 1980, around eight months after its launch. The crew of Challenger made two EVAs (on 8 and 11 April) to first capture the satellite, and then replace the faulty components.

The process of capturing the SMM did not go smoothly. As it had lost attitude control, it was slowly tumbling through space, and would have to be stabilised before it could be grappled by the shuttle's Canadarm robotic manipulator. To do this, rookie astronauts James van Hoften and George Nelson went out on a spacewalk to capture the satellite and halt its rotation using their Manned Maneuvering Units (MMUs) – thruster packs that attached to their spacesuits.

However, when George Nelson reached the SMM, he discovered that the hardware he'd been given to latch onto the satellite wouldn't attach properly. He attempted to connect a few times, but succeeded only in bumping the satellite and increasing its rotation. Nelson then tried grabbing the satellite by one of its solar panels, which seemed to only make its movement more erratic. The two astronauts returned to the Shuttle without having brought the SMM under control.

As it turned out, the agitation of the satellite shook things up enough that the controllers on the ground were able to momentarily regain control of the SMM's systems and fired thrusters to stop it spinning. The Shuttle crew were then able to grapple the SMM using the Canadarm and dock it with a special mount in the cargo bay. During a second spacewalk, van Hoften and Nelson were able to make the necessary repairs and replace the faulty components. They called themselves the "Ace Satellite Repair Company".

The satellite was then released back into orbit. It remained operational until November 1989, and its instruments allowed researchers to greatly improve our understanding of solar flares and sunspots. It also led to the discovery of ten new comets.