NASA’s James Webb Space Telescope (JWST) launch date has been delayed for a second time in the past six months. The telescope, which will be the successor of the famed Hubble, was set to be launched in the spring of 2019, but has now been postponed to May 2020, the agency announced on March 27, 2018.

Upon launch, the ambitious $8.8 billion project will be the most powerful and technically complex space telescope in history. The project has been under development for two decades since it was proposed back in 1996.

JWST will study every phase in the history of the Universe, ranging from the earliest stars and galaxies in the Universe, the formation of solar systems capable of supporting life on planets like Earth, to the evolution of the Solar System.

The decision to delay the telescope’s launch came after an independent assessment Standing Review Board (SRB) determined that more time is needed to complete some final stage tasks. These include integrating the 6.5-meter telescope and science payload element with the spacecraft element and testing the components.

Testing the components and their integration is essential to ensure that the observatory can deploy its sunshield, primary and secondary mirrors and then operate properly once it is in space.

The assessment comes after Government Accountability Office expressed concerns over the telescope’s delays and cost overruns back in February, Science Alert reports. NASA also said it may exceed the $8.8 billion budget to complete the project.

When JWST was proposed over 20 years ago, the space agency estimated that the cost of the telescope would range between $1billion and $3.5 billion; however the cost has been increasing over the years. In 2011 U.S. Congress mandated that the project may not surpass $8 billion budget for the development-and-construction phase of the mission.

NASA will work with European Space Agency (ESA) to determine a new date for the launch of Ariane 5 which will deploy the telescope. Once the launch date is fixed, NASA will provide a cost estimate for the project. The space agency in collaboration with independent review boards is now working on a report about the delays and cost increase for Congress.

“We don’t really fully know what the exact cost will be, if we go one dollar over, we will be in a breach condition,” said Thomas Zurbuchen, the associate administrator for NASA’s Science Mission Directorate, The Atlantic reports.

Despite the hiccups along the way, NASA is still fully committed to the JWST project. “Considering the investment NASA and our international partners have made, we want to proceed systematically through these last tests, with the additional time necessary, to be ready for a May 2020 launch,” said Zurbuchen.