Hubble’s final servicing flight was designated STS-125. Also called Servicing Mission 4, it flew Space Shuttle Atlantis to the observatory in May 2009 and became the fifth and final shuttle mission to service Hubble.
The mission launched on May 11, 2009, and lasted nearly 13 days. Its astronauts carried out five spacewalks, replacing or upgrading major systems and instruments. They installed Wide Field Camera 3 and the Cosmic Origins Spectrograph, repaired the Advanced Camera for Surveys and Space Telescope Imaging Spectrograph, and replaced gyroscopes, batteries, insulation, and a Fine Guidance Sensor.
STS-125 was nearly canceled after the 2003 Columbia disaster because Hubble’s orbit could not provide the same safe-haven option as an International Space Station mission. NASA later reinstated it after safety improvements and extensive planning. A rescue mission, STS-400, was kept ready in case Atlantis suffered serious damage.
The other choices were earlier Hubble missions: STS-61, STS-103, and STS-109. STS-125 was the final servicing flight, not merely the latest one at the time.