How a tiny, misplaced washer nearly destroyed the world's most famous space telescope
In short: The Hubble Space Telescope was a forty-year dream designed to peer into the deep universe. Yet, upon launch, it was a disaster. A single, one-millimetre washer left in a testing rig caused the primary mirror to be polished into the wrong shape, rendering its vision no better than ground-based telescopes.
The concept of a space-based telescope predates the space age, rooted in the desire to escape the atmospheric scintillation that blurs ground-based observations. In 1945, Lyman Spitzer proposed a design for the RAND Corporation, envisioning a massive instrument with an aperture of at least 200 inches. By the 1970s, NASA adopted a more modest 2.4-meter design, influenced by existing spy satellite technology. The project eventually launched in April 1990, but the initial results were humiliating. The telescope's optical system was flawed, turning the mission into a public relations catastrophe.
The root cause was a simple human error at the contractor, Perkin-Elmer. A washer, merely a millimetre thick, remained in the mirror-shaping test equipment, leading technicians to grind the primary mirror to an incorrect curvature. Because the telescope was in low Earth orbit, it was uniquely positioned for a rescue. In December 1993, astronauts aboard Endeavour installed corrective optics known as COSTAR—a solution partly inspired by the design of a hotel showerhead. The fix was immediate, restoring the telescope's ability to capture iconic imagery.
Once operational, Hubble revolutionized astronomy, capturing everything from the 1994 impact of Comet Shoemaker-Levy 9 on Jupiter to the early universe via the Hubble Deep Field. It also provided profound insights into the life cycles of stars. For instance, Hubble revealed the complex, diverse structures of planetary nebulae—brief, 10,000-year phases where intermediate-mass stars like the Sun shed their outer layers. These observations, often showing the influence of magnetic fields or binary systems, transformed our understanding of cosmic origins and the final stages of stellar evolution.
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Sources
- Summary by Intellect · source: A Mirror in the Sky - Chris Lintott
- Also: A Mirror in the Sky
- Also: podcast.gresham.ac.uk — A Mirror in the Sky - Chris Lintott - Gresham College Lectures
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