Hubble turns 20
Two days ago, scientists around the world celebrated the 20th anniversary of the Hubble Space Telescope’s launch.
On April 24th 1990, space shuttle Discovery blasted off from Kennedy Space Centre, reaching the then second-highest orbit of 600km, in order to release Hubble well clear of the atmosphere.
Scientists found Hubble’s initial images blurry, and the culprit was deemed to be the the primary mirror used to collect the image. It had been ground incorrectly, causing the image it reflected to become spread out over a wider area than it should be.
Worse still, despite designing the telescope to be serviceable by subsequent shuttle missions, the mirror could not be replaced in orbit. Two backup mirrors had been made by other companies, in case they were needed prior to launch, and the only way they could be fitted was in a costly mission in which Hubble was returned to Earth, repaired and relaunched. At this point, NASA and Hubble had become the butt of many jokes.
What could be done? Ingeniously, knowing exactly how incorrect the mirror’s shape was meant that NASA could actually build some corrective optics that pre-emptively “corrected” the shape of the light before it reached the mirror, in effect distorting the image that the mirror would receive, so that the mirror’s own distorted shape could then even out the distortion and give the expected image.
In 1993, Hubble became fully operational, and continues to provide scientists with stunningly detailed images of the cosmos.
Having had its final servicing mission in mid-2009, Hubble is now on it’s final run before some critical piece of hardware fails. Originally, the telescope was to be collected via shuttle and returned to Earth, probably ending up in a museum. However, the cost of such a mission, combined with the retirement of the shuttle, makes this impractical. Instead, a mount was added on the last servicing mission to allow a later robotic mission to attach a booster to deorbit the shuttle in a controlled fashion.
This is Hubble, as seen for the last time by human eyes.
Get some great wallpaper-sized images of the fruits of Hubble’s labours over the past 20 years from NASA’s Hubble site.
