Divers discovered a large dent
The booster used on the Ares 1-X test rocket on Wednesday was damaged when it fell back into the ocean, the US space agency (Nasa) says.
The recovery team sent to retrieve the stage from waters east of the Kennedy Space Center found a large dent in the side of the booster.
Nasa said the damage resulted from failures in the parachute system.
The Ares 1-X was a demonstrator for the vehicle Nasa plans to use in the next decade to launch astronauts into orbit.
Wednesday's two-minute sub-orbital mission was intended to help verify design assumptions so that when the final vehicle is built, the engineers can be confident it will fly as expected.
Once the first-stage booster had completed its burn, it separated from a dummy upper-stage and all the elements fell back to Earth.
Nasa expected the simulation stage to be destroyed, but engineers wanted to inspect the booster.
The powered part of the flight appeared to go well
It had a parachute system to slow its descent towards the ocean, and it now appears two of the three chutes malfunctioned.
The booster would have hit the water harder than expected, causing the dent later discovered by recovery divers.
Ares managers said they were not too concerned by what had happened because the booster was never going to be used a second time.
"Don't play this too much," said Bob Ess, the 1-X mission manager.
"The parachute thing was like 'Hey, look at that'. We're not worried about that. There's no investigation. There's no unusual thing we're doing. We're just going through our usual post (flight) tests," he was quoted as saying by the Associated Press.
The parachute system would be studied to determine why it had not worked properly, he added.