NASA delays next-generation space telescope until 2020

For such a highly complex machine designed to "look at the universe in a way that we've never seen it," there can be no shortcuts, he stressed. The telescope will study planets orbiting other stars, while probing the earliest times of the cosmos. Some mistakes were made while preparing the telescope, which slowed work. At the same time, NASA underestimated the scale of the job, Zurbuchen said.

Unlike Hubble, which was serviced regularly by space shuttle astronauts, Webb will orbit the sun at a point about 1 million miles (1.6 million kilometers) from Earth, unreachable in case of a breakdown. Hubble lifted off in 1990 with a flawed mirror that blurred its vision; spacewalking astronauts had to fix it in 1993.

"You've heard this before, but it rings true for us. Really, failure is not an option," Zurbuchen told reporters in a teleconference.

NASA and its partner, the European Space Agency, will firm up a new launch date, now tentatively targeted for May 2020 from French Guiana. An independent review board is being formed to look into the remaining work and feasible launch dates.

Once a date is actually set, NASA said it will provide a new cost estimate. Officials acknowledge the cost may exceed the USD 8 billion development cap set by Congress. NASA already has poured USD 7.3 billion into the telescope, said Acting Administrator Robert Lightfoot. He promised Congress would receive a detailed report on schedule and cost this summer.

The telescope is named after the NASA administrator who oversaw the Mercury and Gemini programs and development of the Apollo moon missions. All its parts are now at Northrop Grumman Aerospace Systems in Redondo Beach, California. The two halves of the 13,500-pound (6,100-kilogram) observatory still must be joined and the entire structure tested.

"Extensive testing is the only way to ensure that the mission will succeed with high confidence," Zurbuchen said. In addition to a mirror 21 feet (6.5 meters) across, Webb will sport a five-layer sunshield the size of a tennis court so it can make infrared observations at frigid temperatures. Several tears across all five layers occurred during folding and deployment of the sunshield during testing. The spacecraft's propulsion system also had its share of trouble.

NASA, meanwhile, is launching a planet-hunting spacecraft named Tess on April 16 from Cape Canaveral. Tess will serve as a scout for Webb, identifying planets around nearby stars that Webb later will study for possible signs of life.