How Close Was the Hubble Space Telescope to Failure in the Early 1990s?

The Hubble Space Telescope is famous for capturing incredible images of our universe such as Pillars of Creation, which shows stars forming in clouds of interstellar gas and dust in the Eagle Nebula, almost 7,000 light-years away.

More than three decades after the Hubble Space Telescope became operational, it’s easy to forget that the telescope had an incredibly rocky start. Soon after it was launched into low Earth orbit by the space shuttle Discovery in 1990, it became clear that something was wrong. There was a "spherical aberration" with the telescope's main focusing mirror. Perkin-Elmer, the company that had produced the mirror for NASA, had polished it too flat.

Although the aberration was just 1/50 the width of a human hair, such a discrepancy was enough to cause many of Hubble’s deep-space images to appear blurry. The problem was an expensive embarrassment for NASA, though Hubble was still able to collect invaluable data about the universe. And even its slightly fuzzy images were much better than what a telescope on the ground could capture.

STS-61, the mission to fix the Hubble Space Telescope, took place in December 1993, with astronauts aboard the space shuttle Endeavour performing incredibly complex maneuvers to install the COSTAR system, essentially fitting the telescope with a set of $50-million corrective optics. Training for the mission required years of careful preparation. During five consecutive days of spacewalks, astronauts Story Musgrave, Jeff Hoffman, Kathy Thornton, and Tom Akers worked in teams to fix Hubble, using 200 specially-designed tools.

Luckily, the story has a happy ending. The repair was a resounding success, allowing Hubble to transmit much sharper images back to Earth. A total of five servicing missions, including STS-61, have taken place from 1993 to 2009 to keep Hubble operational.

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