Five spacewalks over an 11-day December 1993 shuttle mission let seven astronauts install corrective optics that effectively gave Hubble “glasses,” restoring the telescope’s blurred vision.
A 2.2-micrometer error in the 2.4-meter mirror’s outer edge had scattered light in every image after launch, turning NASA’s flagship observatory into a public embarrassment.
Investigators traced the flaw to a null-corrector test device mis-set by 1.3 millimeters; the mirror was polished precisely to that wrong measurement, while warning signs from other tests were dismissed.
WFPC2 replaced Hubble’s original camera with built-in correction, while the COSTAR package used small mirrors to fix light for three other instruments after one instrument was removed.
The repair transformed Hubble from a “techno-turkey” into one of astronomy’s most productive tools, later helping measure the universe’s age and support the discovery of dark energy.