STS-109 (SM3B) was a Space Shuttle mission that launched from the Kennedy Space Centre on 1 March 2002. It was the 108th mission of the Space Shuttle Programme, the 27th flight of the orbiter Columbia and the fourth servicing of the Hubble Space Telescope It was also the last successful mission of the orbiter Columbia before the ill-fated STS-107 mission, which culminated in the Columbia Disaster.

The Hubble Space Telescope (HST) was placed in orbit during mission STS-31 on 25 April 1990. Initially designed to operate for 15 years, plans for periodic service and refurbishment were incorporated into its mission from the start. After the successful completion of the second planned service mission (SM2) by the crew of STS-82 in February 1997, three of HST's six gyroscopes failed. NASA decided to split the third planned service mission into two parts, SM3A and SM3B. A fifth and final servicing mission, STS-126 (SM4) launched 11 May 2009 The work performed during SM4 is expected to keep HST in operation through 2014. Further plans for servicing after SM4 are ambiguous as NASA is planning to launch HST's successor, the James Webb Space Telescope in 2014.

The purpose of STS-109 was to service the Hubble Space Telescope (HST). It was Columbia's first flight following an extensive two and a half year modification period (its most recent mission being STS-93). During the mission the crew installed a new science instrument, the Advanced Camera for Surveys (ACS), new rigid solar arrays (SA3), a new Power Control Unit (PCU) and an experimental cryocooler for the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). Columbia also reboosted HST to a higher orbit.

Space shuttle Columbia launches on mission STS-109.
STS-109 Launch

Astronauts remove the FOC to make room for the ACS
The STS-109 astronauts performed a total of five spacewalks in five consecutive days to service and upgrade the Hubble Space Telescope. The spacewalkers received assistance from their crewmates inside Columbia. Currie operated the Shuttle's robot arm while Altman was her backup. Carey and Altman documented the EVA activities with video and still images.

Accomplishments of the spacewalks included the installation of new solar arrays, a new camera, a new Power Control Unit, a Reaction Wheel Assembly and an experimental cooling system for the NICMOS unit. STS-109 accumulated a total of 35 hours, 55 minutes of EVA time. Following STS-109, a total of 18 spacewalks had been conducted during four Space Shuttle missions to service Hubble (the others being STS-61, STS-82, STS-103 and STS-125) for a total of 129 hours, 10 minutes by 14 different astronauts.

Hubble on the payload bay just prior to being released by the STS-109 crew.
It was also the last successful flight of Columbia, as on its next mission, STS-107, it disintegrated on re-entry, killing all aboard.

STS-109 is considered a night launch, as sunrise was at 6:47 am, and Columbia launched at 6:22 am EST, 25 minutes before sunrise.