Kelly, 46, has flown on the shuttle three times since joining NASA in 1996. He now has the job of commander of shuttle Endeavour as it delivers a multi-million-dollar physics experiment to the International Space Station. The mission, tentatively scheduled for April, promises to be one of the most heavily scrutinized and high-profile shuttle flights in history, because it's the final flight on the books before the shuttle fleet is retired.
Giffords was shot and critically wounded while meeting with constituents Saturday at a Tucson, Ariz., shopping center. Six other people, includng a judge and a 9-year-old girl, were killed.
"Our thoughts and prayers go out to Congresswoman Giffords, her husband Mark Kelly, their family, and the families and friends of all who perished or were injured in this terrible tragedy," NASA administrator Charles Bolden said in a statement.
An astronaut's training so close to launch is all-consuming. A shuttle crew a few months from liftoff spends multiple hours in flight simulators and rehearsing their duties in orbit, squeezing time away from work to nearly zero. Combining that schedule with a family tragedy is likely to impose huge pressure on Kelly if he decides to continue with his command of Endeavour's mission.
Kelly is also distinctive as half of the first pair of blood relatives to be in the astronaut corps at the same time. His twin brother, Scott, is currently commander of the space station -- meaning he's living nearly 200 miles above the Earth and unable to be with his brother. Scott Kelly is slated to return to Earth in March.
The Kelly twins grew up in New Jersey, the sons of a police officer, before becoming Navy test pilots.
Mark Kelly's previous marriage ended in divorce. He began dating Giffords well before she was elected to Congress. When he was orbiting in the space shuttle Discovery in 2006, Giffords chose U2s "Beautiful Day" to inspire him as he woke every day. The couple married in 2007.
Kelly has two daughters from his previous marriage.