Who was the first NASA astronaut to go into space twice?

Lieutenant Colonel Virgil Ivan "Gus" Grissom (April 3, 1926 – January 27, 1967) was one of the original NASA Project Mercury astronauts, a United States Air Force test pilot, and a mechanical engineer. He was the second American to fly in space, and the first member of the NASA Astronaut Corps to fly into space twice. Selected as one of the Mercury Seven astronauts, Grissom was the pilot of the second American suborbital flight, in the Liberty Bell 7. The hatch of the craft blew off and filled with water, causing it to sink to the bottom of the ocean.

His next flight was in the Project Gemini Program in a craft named the Molly Brown, which was a successful mission. He was killed along with fellow astronauts Ed White and Roger Chaffee during a pre-launch test for the Apollo 1 mission at Cape Canaveral Air Force Station (then known as Cape Kennedy), Florida. He was the first of the Mercury Seven to die. He was a recipient of the Distinguished Flying Cross and, posthumously, the Congressional Space Medal of Honor.

Grissom enlisted in the United States Army Air Forces as an aviation cadet during World War II. As the end of the war neared, Grissom sought to be discharged and married Betty Moore. Grissom enrolled at Purdue University, graduating with a bachelor's in mechanical engineering in 1950. He reenlisted in the United States Air Force, earning his pilot's wings in 1951. Grissom flew over 100 combat missions during the Korean War.