Malcolm Scott Carpenter, the Mercury astronaut who became the second American to orbit the Earth in 1962, has died at the age of 88. One of the original seven Project Mercury astronauts, Carpenter also became an aquanaut after leaving NASA to work with the Navy’s SEALAB project.

His wife, Patty Carpenter, announced the news on Thursday. While no official cause was given, Carpenter had recently entered hospice care after experiencing a stroke. His passing leaves John H. Glenn Jr., the first American in orbit and fifth human in space, as the sole surviving member of the original Mercury Seven.

"We, the whole NASA family, are mourning with Scott's family," said NASA Administrator Charlie Bolden in a statement. "We have lost a true pioneer. I shall long remember him not only for his smarts and courage but his incredible humor. He kept us all grounded. We will miss him greatly."

Born in Boulder, Colo., Carpenter attended the University of Colorado, studying aeronautical engineering before entering the military. He was a fighter pilot during the Korean War and then he trained as a test pilot before being selected as an astronaut for NASA’s Project Mercury, the United States’ first-ever manned spaceflight program. Alongside Alan Shepard, Virgil Grissom, John Glenn, Wally Schirra, Gordon Cooper and Deke Slayton, Carpenter became a national celebrity and one of NASA’s first public faces.

“I volunteered for a number of reasons,” Carpenter wrote in “We Seven,” a 1962 book examining the Mercury Seven. “One of these, quite frankly, was that I thought this was a chance for immortality. Pioneering in space was something I would willingly give my life for.”

Later that year, Carpenter would get his shot at immortality.

Carpenter was originally assigned as a backup for John Glenn, who manned the United States’ first orbital mission on Friendship 7 in February 1962. Carpenter served as Glenn’s Capsule Commander and radio link, uttering the famous send-off, “Godspeed, John Glenn” at the mission’s outset.

Though NASA selected Deke Slayton to pilot the next manned mission, he was soon grounded from spaceflight by a heart murmur and Carpenter was chosen to replace him. On May 24, 1962, Carpenter piloted the Aurora 7 spacecraft into orbit, circling the Earth three times and performing science experiments before returning to the atmosphere. On that flight, Carpenter became the second American in orbit, the fourth American in space and the sixth human in space.

Upon Carpenter’s return to Earth, Aurora 7’s navigation equipment malfunctioned, forcing Carpenter to make his reentry using manual controls. Due to the malfunction, Carpenter overshot his planned landing area by some 250 miles. For almost an hour after splashdown, NASA crews feared that he was dead, though he was later found safe in his life raft.

Carpenter would not take part in another spaceflight. In 1963, he took a leave of absence from NASA’s astronaut program to train for the Navy’s SEALAB underwater exploration program. A year later, he lost a large degree of mobility in his left arm after a motorcycle accident and was declared unfit for spaceflight by NASA scientists. As a SEALAB II aquanaut, however, Carpenter spent 28 days at the bottom of the ocean off the California coast in 1965.

Carpenter would later serve as an executive assistant to the director of NASA’s Manned Spacecraft Center and a director of Aquanaut Operations for SEALAB III. He later retired from NASA in 1967 and from the Navy in 1969.