Assembly of the hexagonal segments of the primary mirror, which was done via robotic arm, began in November 2015 and was completed in February 2016. Final construction of the Webb telescope was completed in November 2016, after which extensive testing procedures began. In March 2018, NASA delayed the JWST's launch an additional year to May 2020 after the telescope's sunshield ripped during a practice deployment and the sunshield's cables did not sufficiently tighten. In June 2018, NASA delayed the JWST's launch an additional 10 months to March 2021, based on the assessment of the independent review board convened after the failed March 2018 test deployment. The review also found JWST had 344 potential single-point failures, any of which could doom the project. In August 2019, the mechanical integration of the telescope was completed, something that was scheduled to be done 12 years before in 2007. Following this, engineers now are working to add a five layer sunshield in place to prevent damage to telescope parts from infrared rays of the Sun.