Fixing a Seriously Expensive Mirror: The Hubble Space Telescope

If breaking your $11 shaving mirror causes seven years of bad luck, what happens when you mess up a $2 billion dollar one? The Hubble space telescope repair was designed to show us, in exquisite detail, the farthest reaches of the galaxy. There was one slight problem. It didn’t work because it was technically “broken.” OK, not in the traditional sense of a big crack or shattered glass, but a small manufacturing defect causing distant images to be blurrier than expected. Sure, it was still far better than earth-bound telescopes, but when you’re spending $2 billion, things better be perfect.

Big Bucks: the Hubble Space Telescope Mirror

The main mirror of the Hubble space telescope is a whopper, weighing in at 1,825 pounds thanks to its 7.8-foot diameter main mirror. Imagine trying to hang that on your wall. Its purpose is to collect lots of dim light and reflect it back to a much smaller 12-inch mirror, from which point the image is collected, processed and sent back to Earth.

It took about eight years to build, but it had to wait a few extra years until its April 24, 1990 launch, owing to the 1986 Challenger disaster, which delayed the space program by years. By the time the Hubble was ready to report to work, the price tag approached a cool $2 billion. A life-cycle accounting might put the total price tag closer to $12 billion since an additional 10 (ultra) large were sunk into subsequent maintenance missions.

hubble space telescope main mirror under construction and polishing
The Hubble main mirror with its 1/50th of a hair flaw. Can you see it? Image: NASA

A Fraction of a Hair

When you’re manufacturing a multi-billion dollar deep space telescope, details matter. After the Hubble telescope was yeeted into space, scientists were a bit puzzled at the lower-than-expected image quality of cosmically far away stuff.

Upon further investigation, it turned out that the primary mirror manufactured back in 1979 (remember Hubble was launched in 1990) had a tiny, tiny defect.

The edge of the mirror has a slight discrepancy caused by the mis-calibration of polishing equipment. The difference between the actual and design specs was only 1/50th the width of a human hair, but that was enough to cause major distortion when peeking at stuff billions of light-years distant.

Space Glasses

Since the cosmos doesn’t have a warranty return program, engineers had to figure out a solution. While the Hubble was never designed for an easy main mirror swap, it was designed for future maintenance missions to keep it in tip-top shape—at least for planned improvements and fixes of old or worn components. In fact, there have been five service calls to Hubble space telescope between 1993 and 2009. Next time you gripe about a $125 minimum charge for the plumber to come take a look, consider each space shuttle launch cost $1.5 billion, so those service calls were pricey.

Clever engineers figured out a way to avoid replacing the main mirror by making a sophisticated pair of “glasses” to correct its vision. It’s kind of like figuring out a corrective lens prescription for a nearsighted person rather than replacing their eyeballs.

Anyway, two gadgets were installed to fix Hubble’s eyesight: the Wide Field and Planetary Camera 2 (WFPC2) and the Corrective Optics Space Telescope Axial Replacement (COSTAR). The COSTAR system, designed by Ball Aerospace, consists of five pairs of small mirrors mounted on moveable articulated arms, which corrected the fault in the light beam from the defective main mirror. See? Space glasses.

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