The US space shuttle fleet is to remain grounded until March at the earliest, Nasa officials have said.
The next shuttle flight will not be until at least next March
Engineers need to find a solution to the foam debris problem which re-emerged during Discovery's launch.
Seven members of an oversight panel also say Nasa's latest shuttle efforts were tainted by some of the problems that caused the Columbia disaster.
The official heading the team looking at the issue said it would take until early next year at least to find a fix.
The shuttle fleet was grounded after a large piece of foam was shed from the shuttle's external fuel tank.
"From an overall standpoint we think really March 4th is the time frame we are looking at," said Bill Gerstenmaier, Nasa's new head of space operations and the official overseeing the foam fix.
"The teams are making very good progress. But we're still not complete by any stretch of the imagination."
Nasa chief Michael Griffin told journalists at a press briefing in Washington that there had been complacency in the agency in the past. But that there was now a new culture at Nasa.
"For good or ill - and obviously, it was for ill, a poor choice of words on my part - we in Nasa didn't look in detail at foam shedding from the tank for 113 flights - and shame on us," Dr Griffin said.
Space shuttle Atlantis was due to blast off in September. But Nasa engineers will now have to make modifications to the shuttle's external fuel tank, particularly to an area known as the Protuberance Air Load (Pal) ramp.
Shuttle Atlantis will have to wait for its moment in the limelight
A 1lb (450g) chunk of insulation foam peeled off the Pal ramp area of the tank during launch on 26 July. The issue is important because it was just such a piece of insulation that was shed from space shuttle Columbia's tank in during its launch in 2003.
The foam punched a hole in Columbia's left wing, allowing super-heated gases to enter the vehicle as it attempted re-entry into Earth's atmosphere 16 days later. The shuttle broke up, killing seven astronauts.
Seven members of an oversight panel said Nasa had not learned key lessons that had emerged from the Columbia disaster.
Their "minority report" was contained within the final report by the 26-member Return to Flight task group appointed to evaluate how the US space agency meets the recommendations by the Columbia Accident Investigation Board (Caib).
So much emphasis was placed on trying to meet unrealistic launch dates that some safety improvements were skipped, said the seven members.
"We expected that Nasa leadership would set high standards for post-Columbia work...we were, overall, disappointed," the panellists wrote in the report.
The seven critics included a former shuttle astronaut, former undersecretary of the Navy, a former congressional budget office director, former moon rocket engineer, a retired nuclear engineer and two university professors.
Dr Griffin said that he was "changing the game" on thinking regarding the shuttle's useage by Nasa ahead of its September 2010 retirement.
It was originally calculated that about 28 further shuttle flights would be needed to complete the International Space Station. That prediction was later reduced to about 15.
Now, Dr Griffin said, Nasa was "not trying to get a specific number of flights out of the shuttle system".
He added: "The United States has a commitment to its partners to complete the station. We believe that, absent of major problems, we...can essentially complete assembly of the station with the shuttle fleet in the time that we have remaining."
Space shuttle Discovery blasted off from Kennedy Space Center, near Cape Canaveral in Florida, on 26 July.
DAMAGE TO THE EXTERNAL TANK
The shuttle's two Protuberance Air Load (PAL) ramps act as aerodynamic covers to the various cables and air lines running up the side of the external tank
The PAL ramps are sprayed with insulating foam, like the rest of the tank, to prevent the formation of ice when it is filled with freezing liquid hydrogen fuel
During Discovery's launch a 0.5m long chunk of foam weighing about 450g broke away from one of the PAL ramps. It caused no damage - but a similar incident of foam loss is believed to have caused the Columbia accident in 2003