The launch of NASA’s James Webb Space Telescope has been delayed until May 2020, the US space agency said Tuesday.

The highly-anticipated equipment “currently is undergoing final integration and test phases that will require more time to ensure a successful mission,” NASA said in a statement. The launch had been postponed once before to 2019.

“Once a new launch readiness date is determined, NASA will provide a cost estimate that may exceed the projected US$8 billion development cost,” NASA said, without further clarifying the potential final cost of the project.

The James Webb Space Telescope — named after NASA’s second administrator, in office from 1961 to 1968 — will be the most powerful telescope ever built.

One hundred times more sensitive than its predecessor — the revolutionary Hubble Space Telescope Hubble launched in 1990 — it will be capable of studying the atmosphere of exoplanets located beyond our solar system.