SPACE — NASA’s Hubble Space Telescope is very well known among astronomers and space lovers. The data and images sent from outer space have enriched knowledge about the universe. However, not many people know that the telescope should have failed from the start. How did that happen? Here’s the story.
About 30 years ago, NASA astronauts worked together to save the troubled Hubble. It was perhaps the most daring mission ever planned by scientists up to that time.
Hubble launched in 1990 with faulty optics that produced blurry images. Fortunately, space telescopes orbiting Earth are designed so that they can be physically repaired by astronauts. Yes, it has to be done in the middle of the orbit. But even before Hubble launched, no one expected improvements would be made so early in Hubble’s operation, and in such a dramatic way.
The story begins 14 years earlier, when the giant 2.4 meter mirror that would become the center of the Hubble optical system began to be created. As the largest telescope to be sent into space at that time, Hubble’s mirror had to be built to exact specifications. The contract was awarded to a company called Perkins–Elmer.
Also read: NASA answers Chinese astronomers’ claims that the Xuntian telescope is more sophisticated than Hubble
For three years, technicians worked on the mirror blank. They polish, clean, and of course measure it. Repeatedly to close the error gap. To focus light on a distant galaxy, the mirror’s curvature must be created to an accuracy of just five microns, or 0.005 millimeters.
Because such accuracy is beyond the range of the human eye, technicians use a grid of lasers to measure the mirror’s curvature. The grid is managed by a device called a zero-reflective corrector, a metal rod with a closed end in which there are holes for the laser to pass through and reflect off the bare metal panel.
In 1981, the mirror was completed. Two years later, it was combined with other telescope components, and planned to launch with the space shuttle in 1986. However, tragedy struck.
The Challenger disaster that occurred in January 1986 led to a three-year suspension of space shuttle launches to investigate the accident. Hubble finally sat down in a clean room, and waited. Also Read: 7 Astronauts Killed in Challenger Space Shuttle Crash
On April 24, 1990, the time finally came when Hubble blasted off into space aboard the space shuttle Discovery. He was greeted with cheers by mission controllers and astronomers around the world. But the cheers quickly turned to tears.
Hubble was up and sending images to Earth a few days after its launch, but something went wrong. The images were blurry and rumors swept through NASA’s hierarchy. Has a budget of 1.5 billion US dollars been wasted on a vision-impaired telescope?
On the left, an image of the galaxy M100 taken by Hubble before retouching. While the right is the first image after Hubble was repaired. Image: NASA/STScI
The subsequent investigation discovered what had happened, a huge mistake that had been hidden all this time, like a ticking time bomb. It was discovered that, on one of the zero reflective correctors, paint chips had been peeled off, unnoticed. This shows the bare metal dots being reflected by the laser, rather than what should be reflected. In other words, the zero reflective corrector operates as if it were out of position by 1.3 mm.
The consequence was that the outer edge of Hubble’s primary mirror had inadvertently been adjusted to the wrong specifications. It is made to deal with such situations, but only at two microns. Even though it doesn’t sound big, the mistake had a huge impact.
2023-12-25 13:58:00
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