The Hubble Space Telescope launches with a flawed mirror
A manufacturing error a fiftieth the width of a human hair blurs Hubble's vision until a 1993 repair mission
Quick facts
- Agency
- NASA / ESA
- Launch mission
- STS-31 (shuttle Discovery)
- Flaw
- Spherical aberration in primary mirror
- Corrected
- STS-61 servicing mission, Dec 1993
What happened
The Hubble Space Telescope launched aboard the space shuttle Discovery on mission STS-31 on 24 April 1990. Soon after it began returning data, astronomers found that instead of the sharp, point-like star images they expected, Hubble produced stars surrounded by fuzzy halos of light. The main mirror had been ground with a flaw at its edge, off by roughly a fiftieth the width of a human hair, too small to see by eye but large enough to blur every image the telescope produced, a defect called spherical aberration. NASA corrected the problem with a servicing mission, STS-61, in December 1993, installing an instrument called COSTAR along with a corrective optics package built into a replacement camera, WFPC2. On 18 December 1993, astronomers at the Space Telescope Science Institute watched the first corrected image appear on a monitor, free of the blur that had defined Hubble's first three and a half years.
Why it matters
The repair mission proved that a space telescope in low Earth orbit could be serviced by astronauts rather than simply abandoned or replaced, a capability unique to Hubble among major space observatories, and the corrected telescope went on to produce some of the most cited images and datasets in the history of astronomy.
How we know
NASA Science's own history-of-Hubble page documents both the initial flaw and the successful 1993 correction from mission records; the European Space Agency's Hubble history site independently corroborates the launch date, shuttle mission number, and mirror flaw.
Sources
- NASA Science. The History of Hubble · Primary source (author-declared)science.nasa.gov · Cited as a "primary" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
- ESA/Hubble. Launch 1990 · General sourceesahubble.org · Cited as a "reference" source (no stronger domain match). · Link is live and its text matches the event's key terms (Jul 2026)
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