Being on the ground makes the task both easier and harder. It's easier because unlike JWST they don't have just one chance to get it right. If something goes

Being on the ground makes the task both easier and harder. It's easier because unlike JWST they don't have just one chance to get it right. If something goes wrong, they can just fix it. But it's also a more challenging problem to solve because the Earth's gravity deforms the mirrors, and each segment gets deformed differently, and each segment, in turn, gets deformed differently when the mirror is pointed in different directions. So you have to have an extremely accurate model of the deformation as a function of orientation.