When was Servicing Mission 4 and what was done to the telescope?

Servicing Mission 4 (SM4), the fifth astronaut visit to the Hubble Space Telescope (Servicing Mission 3 was split into two parts) was scheduled for 2006. But on February 1, 2003, the Space Shuttle Columbia, returning from a research mission, broke apart while re-entering Earth's atmosphere.

Shuttles were grounded. Then-NASA Administrator Sean O'Keefe called the Hubble mission off, citing the safety guidelines that had been developed following the Columbia tragedy. The next NASA Administrator, Mike Griffin, revisited the cancellation upon his appointment in 2005, and on October 31, 2006, announced that Hubble would be serviced again.

Another delay occurred in September 2008, only two weeks before the mission was to launch. A malfunction occurred in one of the Hubble systems — the Science Instrument Command and Data Handling Unit (SIC&DH) — that commands the science instruments and directs the flow of data within the telescope before it is transmitted to Earth. A backup system took over, but NASA was unwilling to leave the telescope without another backup in case of future problems. Engineers tested and readied for installation a spare unit that had been constructed when Hubble was first built.

On May 11, 2009, the Space Shuttle Atlantis launched for the Hubble Space Telescope. Over the course of five spacewalks, astronauts installed two new instruments, the Wide Field Camera 3 and Cosmic Origins Spectrograph. They repaired two others, the Advanced Camera for Surveys and Space Telescope Imaging Spectrograph. They replaced Hubble's batteries with new versions, and a Fine Guidance Sensor with a refurbished one; installed six new gyroscopes; and added new insulating panels to areas where Hubble's blankets had broken down. They replaced the SIC&DH and attached a ring-like structure that will allow a robotic module to connect itself to Hubble in the future, in order to guide the telescope through its de-orbit at the end of its life.

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