Updated 6:20 p.m. Eastern with comment from Rep. Smith.

WASHINGTON — NASA announced March 27 that the launch of its next flagship astronomy spacecraft, the James Webb Space Telescope, will be delayed an additional year and that the mission is likely to overrun its $8 billion cost cap.

The agency said that the mission, whose launch had already slipped from October 2018 to May-June 2019 because of technical problems, will now launch “approximately” in May 2020. A formal launch date will come this summer after the completion of additional reviews, including one by a new independent review board.

“With all the flight hardware 100 percent complete, we’re approaching the finish line for launch readiness. However, it looks like we have a ways to go before we cross that finish line,” said Thomas Zurbuchen, NASA associate administrator for science, in a teleconference with reporters that itself experienced an interruption due to a glitch.

During the previous delay, announced in September 2017, NASA officials said that issues with the spacecraft bus and its sunshield led to the slip. This new delay is caused by a combination of new issues as well as a better understanding of the severity of those previous problems.

Among the problems described by Dennis Andrucyk, deputy associate administrator in NASA’s science mission directorate, include contamination of values in thrusters on the spacecraft bus, a problem identified last summer. “We didn’t know what that impact would be at the time” of the previous delay, he said, adding that the valves have since been refurbished and reinstalled.

Another issue has been problems with the deployment of the sunshield, a five-layer membrane the size of a tennis court designed to keep the telescope cold while in space. Deploying and then stowing the sunshield took about twice as long as original expected, with two more “deploy and stow” operations yet to take place.

During those tests, tensioning problems with the cables created what Zurbuchen called a “snagging hazard” that resulted in several small tears in all five layers of the sunshield membrane. Andrucyk said they’re making modifications such as the installation of Kapton springs to ensure the cables remain tensioned and “doghouse” mechanical fixtures that constrain any slack the cables might still develop.

Overall integration and testing of the telescope has also taken far longer than expected, even for those components not suffering technical issues. “We were rather optimistic in how we projected an [integration and testing] schedule,” said Andrucyk. “We’ve added some realism to that.”

NASA officials said on the call they would have a more refined estimate of the launch schedule for JWST in June, after additional reviews. NASA is also establishing an Independent Review Board that will be led by former NASA center director and aerospace executive Tom Young, who has served on many similar reviews of agency programs in the past.

NASA held off on estimating any cost increase for the mission, but in the announcement made it clear that it “may exceed” the $8 billion cost cap established by Congress in a 2011 replan of the mission, when cost overruns and delays threatened the mission with cancellation. The Government Accountability Office, in a recent report, concluded any significant additional delay would cause a cost-cap breach.

“We have briefed the congressional staff about the likelihood of passing this breach mark, and informed them that the observatory is complete,” NASA Acting Administrator Robert Lightfoot said. “It’s just a matter of putting the two halves together and getting the testing done of the total observatory.”

Under provisions of recent appropriations bills, including a fiscal year 2018 appropriations bill signed into law March 23, any overrun beyond the $8 billion cap is treated as the equivalent of a 30 percent overrun under federal law. That requires Congress to formally reauthorize the mission after receiving reports from NASA on breach and its corrective actions. If Congress does not authorize the mission 18 months after receiving those reports, NASA would not be allowed to spend any more money on it other than termination costs.

One key House member sharply criticized NASA for this latest slip. “Today’s announcement that the James Webb Space Telescope launch will slip again and likely go over the $8 billion development cost cap is disappointing and unacceptable,” said Rep. Lamar Smith (R-Texas), chairman of the House Science Committee, in a statement to SpaceNews. “These continued delays and cost overruns undermine confidence in NASA and its prime contractor, Northrop Grumman.”

“The James Webb Space Telescope is a crucial project and an investment in our future. I expect it to be completed within the cap and launched as close to on schedule as possible so we can look forward to the incredible discoveries it will bring,” Smith said in the statement, but did not explain how the mission could remain within that cost cap given those delays.

Scientists were also surprised and disappointed with the news of the lengthy delay. “It’s very unpleasant,” said Marcia Rieke of the University of Arizona, co-chair of the Committee on Astronomy and Astrophysics of the National Academies’ Space Studies Board, which was meeting here when the delay was announced. “This is a much longer delay than any of us have anticipated, and there will obviously be various consequences.”

In the media call, NASA said that even as the studies into JWST delays continues, it is taking steps to improve the management of the mission. That includes additional staff devoted to mission oversight at NASA Headquarters, and placing project managers from NASA’s Goddard Space Flight Center on site at contractor Northrop Grumman’s California facility. Management of JWST at Northrop Grumman will now directly report to the company’s president.

“We’re very confident that with these enhancements, we’ll get to a place that will allow us to have a higher confidence level that the telescope functions as expected before it travels to French Guiana” for launch on an Ariane 5, Andrucyk said.

The delay and likely cost overrun for JWST will have implications that go beyond the completion and launch of the space telescope. Zurbuchen acknowledged that it created perception issues for future large space observatories, like the Wide Field Infrared Survey Telescope (WFIRST), which itself is facing cancellation in the administration’s fiscal year 2019 budget request.

He noted that JWST is far more technically complex that WFIRST, which uses an optical system donated by the National Reconnaissance Office and without major deployable systems like the sunshield. “We’re not going to be in a situation that we are with Webb, in which there’s 10 miracles required,” he said.

The delay in JWST’s launch will also delay the science it will produce. Zurbuchen said that a call for proposals for the first cycle of observations, which were due next month in anticipation of a launch next year, will be postponed, but did not immediately provide a new date. The Space Telescope Science Institute later announced the deadline would be pushed back to no earlier than Feb. 1, 2019.

The delay could also affect the next astrophysics decadal survey, the report prepared by the astronomy community once per decade to determine priorities for space and ground-based observatories. Work on the new decadal was set to start ramping up this year in order to be complete by late 2020, a date that assumed that early JWST science would be complete and could influence the results.

“The question we’re going to discuss with the community overall is when the right time is to do the decadal survey,” Zurbuchen said. He planned to start discussions later in the day at the National Academies with astronomy committees meeting for Space Science Week there. “That discussion requires more than just NASA’s opinion.”