CAPE CANAVERAL, Fla.—NASA aced the most complicated, critical job on its newly launched space telescope Tuesday: unrolling and stretching a sunshade the size of a tennis court. Ground controllers cheered and bumped fists once the fifth and final layer of the sunshield was tightly secured. It took just 1.5 days to tighten the ultra-thin layers using motor-driven cables, half the expected time. The 7-ton James Webb Space Telescope is so big that the sunshield and the primary gold-plated mirror had to be folded for launch. The sunshield is especially unwieldly—it spans 70 feet by 46 feet (21 meters by 14 meters) to keep all the infrared, heat-sensing science instruments in constant subzero shadow. The mirrors are next up for release this weekend. The $10 billion telescope is more than halfway toward its destination 1 million miles (1.6 million kilometers) away, following its Christmas Day send-off. It is the biggest and …