It's been about 30 years since NASA astronauts... Hubble Space Telescope on an extremely daring mission. At the time, it was perhaps the most daring mission scientists had conceived. In short, Hubble was launched in 1990 with defective optics that produced blurry images. Fortunately, however, there is the space telescope that orbits the Earth Soil, is designed to be physically repaired by astronauts. Yes, in the middle of the track.
But even with this capability, before Hubble launched, no one really expected that these repairs would have to happen so quickly - and in such a dramatic way.
The story begins fourteen years earlier, when work was just beginning to 'ground' the gigantic 2.4-metre mirror that would form the center of Hubble's optical system. By far the largest telescope sent into it room At the time, the mirror had to be cut to strict specifications. The contract for this arduous task was awarded to a company called Perkins-Elmer.
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Technicians worked on the blank mirror for three years. They polished, cleaned and of course measured. And they did that again and again. To focus the light from distant galaxies, the mirror's curvature had to be ground to an accuracy of just five microns, or 0.005 millimeters.
Because such accuracy is beyond the sight of the human eye, technicians used a grid of lasers to measure the curvature of the mirror. This grid was maintained by a device called a reflective zero corrector, which is a fancy name for a metal rod with an end cap in which a hole is drilled to allow a laser to penetrate and reflect a panel of bare metal.
In 1981 the mirror was complete; two years later it was linked to the other components of the telescope and would be launched aboard a telescope spaceship in 1986 - only for tragedy to intervene. The Challenger disaster which happened in January of that year led to a three-year halt to space shuttle launches while the accident was investigated. Hubble was waiting in a clean room.
Then, on April 24, 1990, it finally happened as it roared aboard the spacecraft. Space Shuttle Discovery to cheers from mission control and from astronomers around the world.
Yet that cheer quickly turned to tears. Within a few days, Hubble was up and running and sending images back to Earth, but something was wrong. The images were blurry and an icy chill filled the air NASA hierarchy. Was $1.5 billion wasted on a telescope with poor visibility?
A subsequent investigation revealed what had happened: a catastrophic mistake dating back to the grounding of the telescope, which had remained hidden the entire time. time, like a ticking time bomb. It was determined that a paint chip had flaked off on one of the reflective zero correctors, going unnoticed. This exposed a spot on bare metal that the lasers reflected on instead of reflecting from. In other words, the reflective zero corrector operated as if it were 1.3mm out of position.
As a result, the outer edge of Hubble's primary mirror was accidentally ground to the wrong specifications. It was made only two microns too shallow to handle this situation. While that doesn't sound like much, this small mistake had huge consequences. Hubble was designed to concentrate at least 70% of the incoming light into a small circle, but the defective mirror allowed it to concentrate only 15% of that light. Everything else was a blur. Such distortion is called 'spherical aberration'.
When this all came out, NASA became a laughing stock among the public, with talk show hosts making jokes at NASA's expense and politicians demanding answers. In the end, the solution turned out to be tantalizingly simple: what else does an optician do for a nearsighted patient than prescribe him glasses?
So that's what NASA did.
Hubble's optical system was of the Ritchey-Chrétien design, in which the primary mirror reflects light back to a smaller secondary mirror that on Hubble is only 30 centimeters wide. The secondary mirror reflects light back through a hole in the center of the primary mirror, to a focal point behind it where the scientific instruments - that is, spectrographs and cameras - are located. Fixing Hubble required putting something in the optical path before the light reached focus to correct the spherical aberration. These are the "glasses" and the instrument was called COSTAR, the Corrective Optics Space Telescope Axial Replacement.
So a team of seven brave astronauts - Ken Bowersox, Dick Covey, Kathy Thornton, Jeff Hoffman, Story Musgrave and Tom Akers from NASA, as well as the European Space Agency's Claude Nicollier, trained for months in NASA's underwater buoyancy tank, practiced the five spacewalks that would be needed to install COSTAR and replace the original Wide Field and Planetary Camera (WFPC) with a new, more advanced model, WFPC 2. They replaced the defective gyroscopes replaced by new ones. The space walks were considered among the most dangerous spacewalks tried so far.
On December 2, 1993, the seven astronauts flew aboard Space shuttle Endeavor on a mission to save Hubble and NASA itself, because if NASA couldn't fix Hubble, how could it be expected to launch and assemble the rocket? International Space Station a task that would be orders of magnitude more complex?
Endeavor grabbed Hubble with its robotic arm and pulled the orbiting observatory into its open cargo bay. The five spacewalks and repairs were carried out flawlessly by the hero astronauts - and when Hubble then sent images back to Earth, they were perfect.
The mission to repair Hubble turned out to be only the first of many maintenance missions on the telescope over the next sixteen years, although none proved to be as important or dramatic as that first. Ironically, COSTAR was not even necessary in the long run: in subsequent maintenance missions, the old cameras and spectrographs were replaced by new, modern models that could correct the spherical aberration themselves. The last servicing mission, during which the space telescope received a major upgrade, took place in 2009, before the retirement of the space shuttle fleet.
Related stories:
- The best Hubble Space Telescope photos of all time
- Saving Hubble: Astronauts remember the space telescope's first repair mission 20 years ago
- Hubble FAQ: Inside the space telescope's final repair mission
While the James Webb Space Telescope (JWST) may have stolen much of Hubble's attention, but the veteran space observatory is still making crucial discoveries. Hubble has observed this in the past twelve months alone the changing weather and seasons on Jupiter And Uranusdiscovered that material was falling out Saturn's rings are warming the planet's atmospheresaw A double quasar from when the universe was only 3 billion years old and measured the size of the nearest known passageway exoplanet are 1.07 times the diameter of the Earth.
None of the above would have been possible without that courageous mission to save the stricken telescope. The repair mission saved NASA's reputation, but it also secured Hubble's legacy for the next thirty years, a legacy that was both profound and astonishing.
