WASHINGTON - Nasa has said that human and technical errors had caused a fresh delay in the launch of a giant space telescope, which will now not be deployed before March 2021. The James Webb Space Telescope - which Nasa has long expected to replace the fabled Hubble - was initially meant to go into service this year but has faced multiple hitches. The Webb telescope will be the most powerful ever built - about 100 times more sensitive than Hubble - and is to be deployed on a mission to give astronomers an unprecedented glimpse at the first galaxies that formed in the early universe. Its most recent delay was announced in March, when Nasa said blast off would likely be in May 2020. The latest snags stemmed from a variety of human errors, technical problems and even “excessive optimism,” said Tom Young, chair of the Independent Review Board. “The complexity and risk cannot be overstated or overestimated,” he told reporters in a conference call. Nasa administrator Jim Bridenstine said in a video message that the telescope “is going to do amazing things, things we’ve never been able to do before as we hear from other galaxies, and see light from the very dawn of time.” “In space, we always have to look at the long term. And sometimes, the complexities of our missions dont come together as soon as we wish.