Mark Kelly, the U.S. astronaut who commanded the final space shuttle Endeavour flight, says he is retiring to spend more time with his lawmaker wife as she recovers from a gunshot wound to the head.

Kelly said in a statement posted on his Facebook page Tuesday he will retire from NASA and the U.S. Navy on October 1.

Kelly's wife, Representative Gabrielle Giffords, was shot in the head at close range on January 8 at a political event in Arizona. Last week, Giffords was discharged from the hospital but continues rehabilitation therapy.

A spokesman for Giffords said the couple will also write a memoir detailing their lives before and after the shooting. Kelly says the book will be part of Giffords' recovery process.

In May, Kelly commanded Endeavour, the final space journey for that shuttle and the second-to-last mission of NASA's 30-year space shuttle program. Giffords traveled to Florida from Texas to watch the launch.

Kelly was a combat pilot during the first Gulf War and became an astronaut in 1996. He has flown four times to the International Space Station aboard the shuttles Discovery and Endeavour.

Six people, including a federal judge and a nine-year-old girl, were killed in the January shooting spree.

In May, the alleged shooter, Jared Loughner, was declared mentally unfit to stand trial. Experts found the 22-year-old to be schizophrenic and unable to help in his own defense or understand court proceedings.