The Hubble Space Telescope, when it launched in 1990, suffered from a major flaw: a spherical aberration in its primary mirror. This meant the mirror was slightly misshapen, causing light to focus incorrectly, blurring the images it captured.

Here's a breakdown of the problem:

* The Error: The mirror's outer edge was ground 2.2 micrometers too flat, which may seem tiny, but it was significant enough to severely impact image quality.

* The Cause: The error was attributed to a faulty testing device used during the manufacturing process. The device was supposed to measure the mirror's shape, but it had a calibration error, leading to an inaccurate reading.

* The Impact: The blurry images sent back by Hubble were a huge disappointment, and the telescope initially received criticism.

Fortunately, the problem was fixable. In 1993, astronauts embarked on a spacewalk mission to install corrective optics in the telescope, effectively putting on "eyeglasses" for Hubble. This successful mission restored Hubble's vision, allowing it to capture the stunning images we've come to associate with this iconic telescope.