It’s been nearly 30 years since NASA astronauts saved the world. Hubble space telescope on an extremely brave mission. At the time, this was perhaps the most daring mission that scientists could think of. In short, Hubble was launched in 1990 with faulty optics that produced blurry images. Fortunately, the orbiting space telescope SoilIt was designed to be physically repaired by astronauts. Yes, in the middle of orbit.
However, before Hubble was launched, despite this capacity, no one expected repairs to occur so quickly and so dramatically.
The story begins 14 years ago, when work was just beginning to “ground” the giant 2.4-meter mirror that will be the center of Hubble’s optical system. The largest telescope ever launched space At that time the mirror had to be ground to exact specifications. The contract for this challenging 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 this over and over again. To focus the light of distant galaxies, the tilt of the mirror had to be adjusted to a precision of just five microns, or 0.005 millimeters.
Since such accuracy is beyond the vision of the human eye, technicians used a laser grating to measure the curvature of the mirror. This grating was maintained by a device called a reflective zero corrector; This is a fancy name for a metal rod with an end cap that has a hole drilled into it for a laser to enter and reflect off a panel of bare metal.
By 1981 the mirror was completed; Two years later, it was combined with other components of the telescope and prepared to be launched onto a spacecraft. space shuttle In 1986 – only for tragedy to intervene. Challenger disaster The incident, which occurred in January of that year, led to a three-year halt to space shuttle launches while the accident was investigated. Hubble sat in a clean room and waited.
Then, on April 24, 1990, the time finally came and he flew the ship into space. space shuttle Discovery Applause from mission control and astronomers around the world.
However, these cheers suddenly turned into tears. Within days, Hubble became active and began sending images back to Earth, but something went wrong. The images were blurry and an icy cold spread around. NASA hierarchy. $1.5 billion wasted on a telescope with imperfect vision?
A later investigation revealed what happened; It was a disastrous mistake that went so far as to ground the telescope and remained so secret. time, like a ticking time bomb. It was found that a layer of paint had broken off unnoticed on one of the reflective zero correctors. This revealed a spot of bare metal that the lasers reflected from, instead of where it was supposed to reflect. In other words, the reflective zero corrector was operating as if it were 1.3mm out of position.
The result was that the outer edge of Hubble’s main mirror was accidentally ground to the wrong specifications. At just two microns it was made too shallow to handle this situation. Although this may not sound like much, this small mistake had huge repercussions. Hubble was designed to focus at least 70% of incoming light into a small circle, but its faulty mirror meant it could only focus 15% of that light. Everything else was a blur. Such distortion is called “spherical aberration”.
When this all came to light, NASA became a subject of public ridicule, with talk show hosts making jokes against NASA and politicians demanding answers. In the end, the solution turned out to be surprisingly simple: What does an optician do other than prescribe glasses for a myopic patient?
That’s what NASA did.
Hubble’s optical system featured a Ritchey-Chrétien design in which the primary mirror reflected light onto a smaller secondary mirror, which in the Hubble was only 30 centimeters (12 in) wide. The secondary mirror reflects light back through a hole in the center of the primary mirror to the focal point behind it, where the science instruments (i.e. spectrographs and cameras) are located. Correcting Hubble required putting something in the optical path before the light reached focus to correct for spherical aberration. These are “glasses” and the instrument is called COSTAR, Corrective Optical Space Telescope Axis Shifting.
A team of seven brave astronauts; as well as NASA’s Ken Bowersox, Dick Covey, Kathy Thornton, Jeff Hoffman, Story Musgrave and Tom Akers. European Space AgencyAfter months of training in NASA’s underwater flotation tank, Claude Nicollier has been practicing for the five spacewalks that will be required to install COSTAR and replace the original Wide Field and Planetary Camera (WFPC) with a new, more complex model, WFPC 2. They would replace the faulty gyroscopes with new ones. Spacewalks were considered one of the most dangerous walks space walks We tried until then.
Seven astronauts were launched onto the ship on December 2, 1993 space shuttle Endeavor They set out on a mission to save Hubble and NASA, because if NASA couldn’t fix Hubble, how could it be expected to launch and assemble Hubble? international space stationWill it be a much more complex task?
Endeavor grabbed Hubble with its robotic arm and pulled the orbiting observatory into the open cargo bay. Five spacewalks and repairs were performed flawlessly by the heroic astronauts, and when Hubble sent the images back to Earth, the images were perfect.
The mission to repair Hubble proved to be only the first of many maintenance missions to the telescope over the next 16 years, but none as significant or dramatic as the first. Ironically, COSTAR was not even needed in the long term: during subsequent maintenance missions the old cameras and spectrographs were replaced with new up-to-date models capable of correcting spherical aberration themselves. The last maintenance mission in which the space telescope received a major upgrade occurred in 2009, before the retirement of the space shuttle fleet.
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while James Webb Space Telescope While (JWST) has stolen much of the spotlight from Hubble, the veteran space observatory is still making vital discoveries. In the last 12 months alone, Hubble has observed: changing weather and seasons Open Jupiter And Uranusdetected the material falling Saturn‘s rings warming the planet’s atmosphereI noticed something double quasar since when Universe was only 3 billion years old and measured the size of the closest known flyby outer planet to be 1.07 times the diameter of the Earth.
None of the above would have been possible without this daring mission to save the damaged telescope. The repair mission saved NASA’s reputation, but it also secured Hubble’s legacy, both profound and surprising, for the next 30 years.