Nasa hopes a makeshift repair carried out to US space shuttle Discovery makes a safe return to Earth more likely.
"We've got a clear vehicle for de-orbit," said lead flight director Paul Hill, after astronaut Stephen Robinson finished a six-hour spacewalk.
The astronaut used his hands to yank out two ceramic strips protruding from the heatshield on the orbiter's belly.
Nasa was concerned the strips could have caused Discovery to overheat as it re-enters the Earth's atmosphere.
It is the first orbiter flight since Columbia overheated and broke up on re-entry.
However there is still concern about a thermal blanket below the cockpit that was damaged on take-off and which some experts fear could tear off on re-entry.
Mr Hill said a decision would be taken once engineers had finished studying images of the blanket.
The shuttle is scheduled to return to Earth on 8 August.
The US space agency had identified two "gap fillers" that were sticking out between heatshield tiles near Discovery's nose section, each by less than 3cm (1.2in).
The pieces of ceramic fabric, which act like a grouting for the tiles, were probably shaken out during the vibrations of launch, Nasa said.
Experts said protrusions on the otherwise smooth belly of the shuttle could disturb the air flow during re-entry, causing turbulence that raises temperatures on heatshield tiles downstream.
Nasa has never allowed an astronaut to conduct a spacewalk beneath a shuttle's belly before, for fear it could easily be damaged.
Robinson triumphantly held up the pieces he had removed, declaring: "I am just putting it in my trash bag."
A Nasa scientist said the operation was "flawless".
Robinson, who was accompanied on the spacewalk by crewmate Soichi Noguchi, had received instructions in a 12-page e-mail to prepare him for the removal operation.
He is the first person to ever see the underbelly of the shuttle while in orbit and was manoeuvred into position by the ISS's Canadarm2 18m (58-foot) robotic arm.
Made of ceramic-coated cloth, the gap fillers act as seals between Discovery's heat-resistant tiles
Astronaut Stephen Robinson removed a section of protruding filler by hand
There had been concerns it would be difficult to remove the strips, so Robinson had been provided with forceps and a modified hacksaw, but in the end he was able to tweeze the pieces out easily with his fingers.
Columbia was lost with its crew in February 2003 when a suitcase-sized piece of foam fell from its external tank during launch, punching a hole through heatshield panels in the shuttle's left wing.
The damage did not present problems in orbit, but as the vehicle tried to re-enter the Earth's atmosphere, super-heated gases entered the wing and tore the ship apart.
Discovery suffered minor tile damage to its protective tiles at launch because of flying foam debris.
Discovery has sustained minor damage to tile sections close to the front landing gear doors on the underside of its nose
This is one of the parts of the shuttle that experiences greatest heating as it re-enters the Earth's atmosphere
Nasa is confident the nick in the tile will not present a problem but wanted the protruding gap filler removed