Now playing: Watch this: NASA builds the largest space telescope ever

NASA has been planning to launch a powerful new telescope that can see across the universe and perhaps to the beginning of time for many years now. But the launch of the James Webb Space Telescope (JWST) appears likely to have to wait at least two more.

NASA/Ball Aerospace

On Tuesday, NASA said it needs more time to test the $8 billion space observatory, pushing back the scheduled launch date to approximately May 2020 from the previous plan for a spring 2019 blast-off.

"Webb is the highest priority project for the agency's Science Mission Directorate, and the largest international space science project in US history," Robert Lightfoot, NASA's acting administrator, said in a statement. "All the observatory's flight hardware is now complete. However, the issues brought to light with the spacecraft element are prompting us to take the necessary steps to refocus our efforts on the completion of this ambitious and complex observatory."

NASA representatives told reporters on a conference call Tuesday morning that technical issues have emerged over the last year, setting back the timeline for the telescope's launch, including problems with a transducer in the propulsion system, which led to other issues that required fixing.

"Tasks are just taking longer to complete and there's some mistakes that were made," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate.

The telescope must be folded up "origami-style" into the payload bay of an Ariane 5 rocket and has to unfold in space after launch. JWST engineers discovered a potential for snagging and tearing of the telescope's large and complicated sunshield, which is made of a thin material almost as large as a tennis court.

JWST is the successor to the Hubble Space Telescope, which launched back in 1990. Hubble has changed the way we see the universe by probing the mysteries of dark matter, analyzing the atmospheres of exoplanets beyond our solar system and more. When Hubble launched, we hadn't yet spotted the first exoplanet.

JWST is significantly larger and more powerful than Hubble, with more than six times the light-collecting surface area of its predecessor's primary mirror. This should allow the new telescope to see deeper into space and further into the past than any instrument before it. Unlike Hubble, though, JWST will observe primarily in the infrared wavelengths.

Getting James Webb off the ground has been a struggle for over a decade due to a series of earlier delays and cost overruns.

NASA next will prepare a formal report to Congress this summer, which will likely needed to reauthorize continued spending on the project.

First published, March 27, 8:44 a.m. PT.

Update, March 27 at 9:40 a.m. PT: Adds additional information and quotes from NASA.

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