NASA has delayed the launch of its next-generation space telescope until 2020.

Officials say they need more time to assemble and test the James Webb Space Telescope, which is considered a successor to the orbiting Hubble Space Telescope.

The observatory was supposed to fly this year. But last fall, NASA bumped the launch to 2019. NASA announced the latest delay on Tuesday.

“We have one shot to get this right before going into space,” said Thomas Zurbuchen, NASA’s associate administrator of science.

He said some mistakes were made while preparing the telescope, and NASA underestimated the scale of the job.

NASA and its partner, the European Space Agency, will work together to firm up a new launch date, now tentatively targeted for May 2020. Once a new date is set, NASA says it will provide a new cost estimate. Officials say the cost may exceed the $8 billion program cap set by Congress. NASA has already poured $7 billion into the telescope.

All of the telescope’s parts are at Northrop Grumman Aerospace System in Redondo Beach, California.

(AP)