STS-125 was the fifth and final Space Shuttle mission to service the Hubble Space Telescope, and it was the most ambitious of them all. Launching on May 11, 2009, aboard Atlantis, a crew of seven astronauts conducted five spacewalks over five consecutive days — totaling 36 hours and 56 minutes of EVA time — to perform the most complex Hubble servicing ever attempted.

The crew installed two revolutionary new instruments: the Wide Field Camera 3 (WFC3) and the Cosmic Origins Spectrograph (COS). WFC3 would go on to capture some of the most iconic images in astronomy history, including the Hubble Ultra Deep Field and the Pillars of Creation revisited. COS dramatically improved Hubble’s ability to study the ultraviolet light from faint, distant objects. Together, these instruments transformed Hubble into an even more powerful observatory.

The mission also replaced all six of Hubble’s gyroscopes, installed new batteries, replaced a Fine Guidance Sensor, installed new thermal blankets, and — for the first time — repaired two instruments in orbit that were never designed to be serviced: the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys (ACS). These repairs required removing over 100 tiny screws in bulky spacesuit gloves, a feat that astronaut John Grunsfeld described as “brain surgery in space.”

This was Grunsfeld’s third Hubble servicing mission and his fifth spaceflight. The mission was unique in the post-Columbia era because Hubble’s orbit could not reach the International Space Station, meaning there was no safe haven if Atlantis was damaged during launch. NASA had Shuttle Endeavour standing by on LC-39B for a potential rescue mission (STS-400) — the only time two Shuttles stood ready on the pad simultaneously.

Atlantis released Hubble on May 19, 2009, and landed at Edwards Air Force Base on May 24. The telescope was expected to function for another five years; instead, thanks to STS-125, Hubble continues to operate more than 15 years later, working alongside the James Webb Space Telescope to expand humanity’s understanding of the cosmos.