After a series of delays and billions spent over budget, the potent James Webb Space Telescope is on track to launch in 2018 at a total project cost of $8.8 billion, NASA vowed on Tuesday.

The project, which aims to build the world's most powerful telescope, 100 times more sensitive than the Hubble space telescope, has been riddled by poor management and cost overruns.

Though a Congressional subcommittee threatened to ax the project altogether earlier this year as lawmakers grappled with how to reduce a more than $15 trillion national deficit, Congress has since agreed to fully fund it at the level NASA requested.

But NASA's new JWST program manager Rick Howard who came on board last year, still faced an acrimonious grilling on Tuesday from lawmakers in the House Committee on Science, Space and Technology.

Committee chair Ralph Hall described the project as "another case study of NASA mismanagement" and said the NASA reshuffle was "the agency's last opportunity to hold this program together."

"We have changed the management, the priority and the approach," Howard told the committee hearing. "We can deliver JWST within costs."

In February, NASA inspector general Paul Martin told lawmakers that the telescope had gone way over its initial budget of $3.5 billion and was likely to come in at around $6.5 billion.

NASA has also pushed back its scheduled launch -- initially set for 2013 -- numerous times. It is now set for October 2018.

Garth Illingworth, an astronomer and professor at University of California, Santa Cruz, was part of an independent comprehensive review panel (ICRP) that reviewed NASA's work on the JWST and issued a report last year.

"I feel that NASA has actually done a very good job on this replan. They have developed a plan that is I would say uniquely conservative for NASA in the level of reserves and the approach that they are taking," Illingworth told lawmakers.

"They realized that they had seriously flawed management before the time of the ICRP and are trying to rectify it, as Rick said," he added.

"I am highly encouraged by what I have seen over the last six to nine months on this program."

Republican lawmaker James Sensenbrenner asked how the US space agency would carry out any repairs on the telescope, recalling how the orbiting Hubble needed numerous service missions by the space shuttle program, which retired this year.

"We don't have the shuttle anymore. What is going to happen if we need to repair the James Webb Space Telescope or if we find out some the parts were not properly done?" he asked.

Howard responded that NASA was already in the process of testing and checking the mirrors at operating temperature, and noted that the telescope's path would take it beyond where the world's spacecraft have the capacity to carry humans, anyway.

"We know that we only have one chance to get this right," Howard said.

"It is not going to be in orbit around the Earth, it is going to a distance four times further away than the moon. So we are taking every step we can to mitigate the risks to make sure that we do have a system that can work."

"You've just increased my skepticism given the history, and I have been on this committee longer than anybody else," Sensenbrenner answered.

"I can see another money pit coming up."