The mirrors of the James Webb Space Telescope are designed to peer at the Universe's first stars. Credit: Desiree Stover/NASA

NASA will delay the launch of its ambitious James Webb Space Telescope (JWST) by nearly a year, until approximately May 2020. That is likely to push the cost of the mission — the most complex space-science telescope ever built — over the US$8-billion limit set by the US Congress. It is the first major setback since NASA revised its plans for the project in 2011, after years of slipping schedules and rising costs.

NASA announced the delay on 27 March, saying that engineers needed more time to assemble and test the components of the spacecraft at its main contractor, Northrop Grumman in Redondo Beach, California. Among other problems, the collapsible, tennis-court-sized sunshield that protects the observatory’s 6.5-metre mirror took weeks longer than expected to fold and refold during testing.

"Frankly, the tests are taking longer to complete than expected," Robert Lightfoot, NASA's acting administrator, told reporters.

The agency did not say how much the delay would cost, but some estimates suggest that it could add a few hundred million dollars to the project. In recent years, Congress has pushed NASA hard to hold down the cost of the telescope and other future missions.

The delay will affect NASA’s astrophysics budget more broadly, including its next big planned space observatory, the Wide-Field Infrared Survey Telescope (WFIRST). The agency had aimed to spend more on WFIRST in the coming years as its contributions to JWST shrank, trading off the end of one mission’s development for the beginning of another. Now, the JWST delay risks compounding problems for WFIRST. Last month, President Donald Trump proposed cancelling WFIRST; astronomers protested, and Congress has restored it for now with a $150-million injection of funds.

US astronomers ranked JWST and WFIRST as the most important large space missions, respectively, in decadal surveys of their scientific priorities released in 2000 and 2010.

Off target

NASA delayed the JWST launch after an independent board of experts concluded this month that the project could not meet its goal of a June 2019 launch. The agency had recently shifted to that target, abandoning﻿ the October 2018 launch date it had aimed for since rebooting the project in 2011. Now, yet another independent panel — chaired by former aerospace executive Tom Young — will review the project's schedule. Based on these reviews, NASA will decide on a more-specific launch target in the coming months.

"We have one shot to get this right before going into space," says Thomas Zurbuchen, NASA's associate administrator for science.

Until recently, project managers were able to deal with schedule problems by moving work tasks around locations. For instance, engineers decided to clean the telescope’s mirror at NASA’s Johnson Space Center in Houston before shipping it to the crowded spacecraft-assembly facility at Northrop.

Northrop staff are now working 3 shifts, 24 hours a day, but cannot work on enough parts simultaneously to stay on schedule. The increased number of workers is adding to the project’s overall cost, the US Government Accountability Office reported last month.

There are other problems, too. In April 2017, a technician applied too high a voltage during a test, damaging components of the propulsion system that took more than a month to replace. In October, engineers discovered several tears in the sunshield caused by a “workmanship error”. And part of the five-layer sunshield snagged during a deployment test.

NASA will send senior managers to California, making sure that one is always present at the Northrop facility. In a statement, Northrop said that it “remains steadfast in its commitment to NASA and ensuring successful integration, launch and deployment of the James Webb Space Telescope”.

Plans in disarray

All the testing is crucial because JWST will operate from an orbit about 1.5 million kilometres from Earth, where it cannot be serviced by astronauts as the Hubble Space Telescope was. JWST will be 100 times more powerful than Hubble, and will survey the Universe mainly in infrared wavelengths. Among the many celestial phenomena that it aims to explore are the first stars and galaxies to form in the Universe, as well as planets in and beyond the Solar System.

NASA had asked scientists to submit proposals by next week for JWST's first set of observations, but the agency has cancelled that deadline. "We'd rather have it launch later and work perfectly than rush and have problems," says Emily Levesque, an astronomer at the University of Washington in Seattle who had been working up a proposal. "But there are going to be a lot of people considering what this means for astronomy and for future missions."

Zurbuchen said he was starting discussions about whether astronomers should delay the next decadal survey, which had been slated for 2020. "Should that be done when we have real data from Webb in our hands, or before?" he asked.

Follow the money

The delay means that NASA will need to agree to a new schedule with the European Space Agency, which is to launch JWST from its spaceport in French Guiana. NASA will also have to figure out how to accommodate the extra costs — perhaps by taking them out of the operations budget for JWST, penalizing Northrop or delaying WFIRST or other projects. NASA has spent $7.3 billion on the project so far, Lightfoot said; spending more than $8 billion would need to be reauthorized by Congress.

WFIRST recently underwent a cost-cutting exercise following its own independent review. Mission managers are reducing some of its science capabilities to keep it below a $3.2-billion budget cap.

JWST and WFIRST are very different technologically, says Jon Morse, chief executive of Boldly Go Institute, a space-exploration organization in New York City, and former head of NASA’s astrophysics division. JWST involves complex designs that have never been tested before, such as the enormous sunshield. WFIRST will use a well-understood 2.4-metre mirror design that does not require lots of new technology.

“WFIRST is not likely to develop the cost problems of the same magnitude as JWST,” Morse says.