alt Hacker NewsThe spherical aberration of Hubble's main mirror was caused by a manufacturing defect.
Perkin-Elmer designed a new null corrector to verify that the mirror was made to spec, but the null corrector was incorrectly assembled (one of the lenses was out by a few mm). They also used the previous null corrector to test, which showed that the mirror was incorrectly ground, but decided that the new null corrector's measurements was correct.
But wouldn't they have needed to do that for KH satellites too? If they're making new equipment and processes, they'll be saving a lot less money from using KH mirrors