During Discovery's launch Tuesday, a large piece of the insulating foam broke off the tank but did not put the shuttle in danger as it did during the January 2003 liftoff of the shuttle Columbia.
In Columbia's case, when the orbiter tried to re-enter Earth's atmosphere after its two-week mission, the damage on the wing from the foam strike caused the shuttle to burn up in the sky above Texas.
"Call it luck or whatever, it didn't harm the orbiter," shuttle program manager Bill Parsons said of Discovery's launch. If the foam had fallen earlier in flight, when the atmosphere is thicker increasing the likelihood of impact, it could have caused catastrophic damage to the orbiter, NASA officials said, according to the Associated Press.
Parsons' deputy, Wayne Hale, said the risk was "not acceptable," but emphasized that Discovery was safe to return home on Aug. 7.
A large chunk of foam flew off the redesigned external fuel tank about two minutes after liftoff. After reviewing the video and images taken by the 100-plus cameras in place to watch for such problems, mission managers believed that the foam did not hit the shuttle.
The seven astronauts plan a closer inspection of the spacecraft over the next few days just to be sure.
"You have to admit when you're wrong. We were wrong," Parsons said, reported the AP. "We need to do some work here, and so we're telling you right now that the ... foam should not have come off. It came off. We've got to do something about that.
"We won't be able to fly again," until the hazard is removed," he told reporters Wednesday evening.
The next orbiter, Atlantis, was scheduled to take off in September, but that mission is on indefinite hold.
In addition to the large chunk of foam, several smaller pieces broke off. One of the thermal tiles on Discovery's belly was damaged, but none of the tile damage looked serious enough to require in-orbit repairs, said Hale.
The astronauts have a 100-foot, laser-tipped crane on board that can get 3-D views of any damage. If NASA decides to use the new inspection tool, astronauts will use it Friday, a day after docking with the International Space Station.