Mark Kelly, retired NASA astronaut and husband of former Democratic Rep. Gabby Giffords, announced Tuesday that he will run in 2020 for the Arizona U.S. Senate seat held by Republican Martha McSally.

Kelly, 54, announced the bid in a video posted to his Twitter account.

Mark Kelly TWEET My next mission... FullSpeedAhead ForArizona

"I always knew that I was going to serve this country in some way," said Kelly, who served in the Navy during the Gulf War and was tapped to become a NASA pilot in 1996.

Kelly, a Democrat, highlighted his career as an astronaut in the four-minute video, which he captioned as "my next mission." It begins with him recounting his first experience witnessing a sunrise from a space shuttle.

"It becomes pretty obvious pretty early when you get into space that we're all in this together," he said.