Shortly after it was released into Earth's orbit in April, the
Hubble Space Telescope was diagnosed with a misshapen mirror.
During the mirror's construction, engineers had relied on a
highly sensitive optical instrument known as the "reflective
null" to detect any deviations from the desired curvature.
Unfortunately, the null itself proved to be inaccurate. In
favor of the overly trusted null, engineers ignored other
instruments that may have detected the error, resulting in a
Hubble destined to remain frustratingly out of focus until a
dramatic and successful repair in 1993.