ORLANDO, Fla. -- A former NASA astronaut who commanded space shuttle Discovery's second-to-last mission died after a water scooter crash involving his sons near Pensacola Beach.

Capt. Alan Poindexter, 50, died Sunday after a water scooter driven by his 26-year-old son, Zachary, collided into the back of another one the former astronaut was riding.

"They were both moving and for some reason Capt. Poindexter stopped his watercraft and Zachary for some reason didn't see him stop," said Stan Kirkland, a spokesman for the Florida Fish and Wildlife Conservation Commission. "Zachary's watercraft went up and struck Capt. Poindexter."

Another son, 22-year-old Samuel, was on Poindexter's scooter. They were thrown into the water. A boat picked up Poindexter and took him to shore. He was talking and complaining about rib injuries but he lost consciousness and was pronounced dead at a nearby hospital.

The accident happened in a bay between Gulf Breeze and Pensacola Beach in Florida's Panhandle where Poindexter had been vacationing. His family has close ties to the area. His wife, Lisa, is from Gulf Breeze, and Poindexter reported to flight training in Pensacola after college.

No charges were filed, Kirkland said, and an exact cause of death would be determined by the medical examiner.

After retiring from NASA in December 2010, six months before the shuttle program ended, Poindexter took a job as dean of students at the Naval Postgraduate School where he had graduated in 1995.

School spokesman Alan Richmond did not immediately comment.

Poindexter, who was known as "Dex," was selected to be in the astronaut corps in 1998. He flew on his first mission a decade later when he was a pilot aboard Atlantis' mission to install the Columbus laboratory at the International Space Station. He commanded Discovery's second-to-last flight in April 2010, a mission to resupply the space station.

"He was a passionate, caring and selfless individual who will be missed by all," former astronaut Leland Melvin, who is now an associate administrator for the space agency, said in a statement released by NASA. Poindexter and Melvin joined the astronaut corps in the same class and flew together in 2008.

The shuttle program ended in July 2011.

The astronaut's father is retired Navy Adm. John Poindexter, national security adviser under President Reagan. Poindexter was born in Pasadena, Calif., but grew up in Coronado, Calif.

During a 2008 interview with The Associated Press, Poindexter said he was inspired to be an astronaut while studying at the Georgia Institute of Technology in the 1980s.

Poindexter became a naval aviator in 1988 and he made two deployments to the Arabian Gulf during Operations Desert Storm and Southern Watch. He worked as a test pilot before he was selected to become an astronaut in 1998.

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