In November, an independent panel recommended the launch date be pushed back from 2014 to 2015, blaming poor program management and overly optimistic schedules, NewScientist.com reported Tuesday.
Now NASA says over-budget telescope, successor to the Hubble Space Telescope, probably will be delayed even further.
Testifying at a congressional budget hearing Monday, NASA Administrator Charles Bolden said the agency now thinks 2018 "is a reasonable launch date."
The November panel said the telescope would require an extra $500 million to hit a 2015 launch date, and warned the launch could slip to 2017 or 2018 with a leaner budget.
Bolden told the Senate hearing he could not request a budget boost in today's economy but that NASA is considering seeking some kind of increase to the project's budget starting in 2012.
"There will be some additional spending that will be required," he said.
Bolden said he hoped to have a new road map for the flagship telescope program by the end of the month.