NASA on Thursday announced that the next-generation space $8.8 billion James Webb Space Telescope’s (JWST) launch has been postponed to the spring of 2019. Citing spacecraft-integration issues, the Space agency admitted that it wasn’t quite ready to go into space despite over two decades of research and development.

“The change in launch timing is not indicative of hardware or technical performance concerns,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate. “Rather, the integration of the various spacecraft elements is taking longer than expected.”

As part of an international agreement with the European Space Agency (ESA) to provide a desired launch window one year prior to launch, NASA recently performed a routine schedule assessment to ensure launch preparedness and determined a launch schedule change was necessary, the Space agency said in its news release.

The 21-foot (6.5-meter) diameter infrared-optimised telescope which will be the world’s most powerful space telescope ever built, is designed to study an extremely wide range of astrophysical phenomena: the first stars and galaxies that formed; the atmospheres of nearby planets outside our solar system, known as exoplanets; and objects within our own solar system.

Consequently, JWST will now launch between March and June 2019 from French Guiana, following a schedule assessment of the remaining integration and test activities, the American space agency said.

All the rigorous tests of the telescope and the spacecraft to date show the mission is meeting its required performance levels, it said. Existing programme budget accommodates the change in launch date, and the change will not affect planned science observations.

“Webb’s spacecraft and Sun-shield are larger and more complex than most spacecraft,” said Eric Smith, programme director for the James Webb Space Telescope at NASA. “The combination of some integration activities taking longer than initially planned, such as the installation of more than 100 Sun-shield membrane release devices, has meant the integration and testing process is just taking longer,” said Smith.

“Considering the investment NASA has made, and the good performance to date, we want to proceed very systematically through these tests to be ready for a Spring 2019 launch,” he said. NASA also confirmed that its existing budget reserves would accommodate the launch delay.

Webb is an international project led by NASA with its partners ESA and the Canadian Space Agency.