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.