By Paul Rincon
BBC News science reporter, at the Kennedy Space Center
Nasa has grounded its shuttle fleet after large pieces of foam debris peeled off Discovery's external fuel tank during Tuesday's launch.
Although none is thought to have hit the orbiter, two shielding tiles on Discovery do appear to be damaged.
Managers described the findings as "unacceptable" and said other orbiters would not be safe to fly until changes were made to the launcher system.
"Until we fix this, we're not ready to go fly again," said Bill Parsons.
"I am personally disappointed that this happened, but it didn't harm the orbiter and we learned something," the space shuttle programme manager added.
Experts have been poring over video and still images of the launch. Discovery's astronauts, too, have been examining the structural integrity of their orbiter with sensor and camera attachments on the end of a long robotic arm.
They also took images from their cockpit of the external tank immediately after it was jettisoned and was beginning its fall back to Earth.
It is now clear a large piece of foam 24-33 inches (61-84 cm) in length had peeled off an area of the tank known as the Pal ramp.
SHUTTLE RETURN TO FLIGHT
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: 1039 EDT, 26 July
Landing: 0546 EDT, 7 Aug
Location: Kennedy Space Center
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda
A six-inch (15cm) foam chunk also fell from an area of the tank called the liquid hydrogen intertank flange. This was an area where several modifications were made after the Columbia disaster.
Officials stressed there was no evidence that either piece of foam had hit Discovery itself.
Mr Parsons said it was too early to say what implications this had for plans to send the Atlantis orbiter into space in the event that Discovery's crew needed to be rescued; but he vehemently denied suggestions that the orbiter system was inherently unsafe.
Of the two heatshield tiles apparently damaged during launch, deputy programme manager Wayne Hale said: "Are we concerned about it? We're treating it very seriously, but we're not losing sleep yet."
A rectangular tile near the nose landing gear doors appeared to be chipped and a square "chine" tile further toward the aft (back) end of Discovery also seemed to have broken away.
On Thursday, Discovery will do a flip manoeuvre before docking with the International Space Station. This will allow the ISS crew to photograph the underside of the spaceship.
Discovery's mission is the first shuttle flight since the loss of Columbia and its crew of seven in February 2003.
Its external tank shed a suitcase-sized piece of foam during launch that punched a hole in the ship's wing, allowing super-heated gases to pierce the airframe during re-entry and pull it apart.
Shuttle programme managers do not believe the foam hit the shuttle
Nasa spent months changing the way the insulation was applied to the tank. It was thought only small pieces of debris would come off during Discovery's launch.
"Perfection is our goal in this business; you seldom get perfection in anything you do. We need to do better than this," said Mr Hale.
"This is a very difficult business, it's not for the faint-hearted and it's not to be undertaken lightly."
Discovery is due to touch down at the Kennedy Space Center on 7 August at 0546 EDT (0946 GMT; 1046 BST).