The Tired Eyes of Hubble and Its Lasting Legacy for Us

As issues continue with the navigation system of the Hubble Space Telescope, NASA has announced that it will attempt to extend the operational period of this tired old instrument by changing its navigation methods; an effort that will come at the cost of new limitations for the scientific observations of this historic astronomical tool. Our growth and leaps in understanding the universe have been directly dependent on the capabilities of the tools we have used to observe and gather data from it. The first use of a telescope for astronomical observations revolutionized data collection from the sky and shaped our understanding not only of the sky but of the structure of the universe. Each time we have been able to increase our ability to gather light in our telescopes, new faces of the universe have emerged before us, leaving us more awestruck by the wonders of the cosmos. However, the increase in the capabilities of ground-based observatories is limited. Our planet is enveloped by a dense atmosphere that has made life possible here. Without this atmosphere, not only would breathing and temperature maintenance be impossible, but high-energy radiation and harmful rays from space could have led to the extinction of life on our blue planet. Yet, this life-giving atmosphere also prevents significant portions of the electromagnetic spectrum from reaching the Earth and disrupts the visible light received from the sky. You have certainly witnessed the twinkling of stars at times; the reason for this twinkling is the passage of starlight through the turbulent layers of the Earth's atmosphere. The light from these stars becomes distorted as it passes through the Earth's atmosphere, and no matter how much we try to neutralize this atmospheric effect in various ways, ultimately our efforts reach a point of impossibility. Due to this barrier that the Earth's atmosphere creates on the quality of observations from the ground, the proposal to build and send an observatory into space has been raised since the 1970s; a large telescope that could take a deep look into the depths of the cosmos. In 1977, the United States Congress approved the initial budget for this project, and a group of scientists and researchers led by Lyman Spitzer, one of the pioneers and advocates of this plan, began its implementation. The European Space Agency joined NASA as a partner in this project to turn the telescope, named in memory of Edwin Hubble, the first discoverer of the universe's expansion, into a global project. The construction of Hubble finally began in the 1980s, but the process was repeatedly delayed due to technical and engineering complexities and budget estimation issues. The disaster of the Challenger space shuttle explosion caused the last long delay for the start of this mission until, about two decades after the proposal was made, Hubble was ready for launch in 1990. The Hubble Space Telescope began its journey into space on April 24, 1990, inside the payload bay of the Discovery space shuttle. The main mirror of this telescope, responsible for collecting light, is nearly 2.5 meters in diameter. In telescopes, the most important factor for image quality is the diameter of the primary mirror. Although 2.5 meters may not seem very large compared to the mirrors of ground-based observatories, when we consider that this mirror can collect light without the interference of the Earth's atmosphere, no ground-based observatory can compete with it. Hubble is positioned in an orbit at an angle of 28.5 degrees to the equator and at a distance of about 540 kilometers from the Earth's surface; an orbit in which Hubble circles the Earth approximately every 95 minutes. One day after the launch of the Discovery shuttle, Hubble was placed into orbit and after initial tests, it sent its first test images back to Earth; images that drew gasps from scientists and engineers. This gasp was not from wonder but due to the distortion observed in the images. Investigations revealed that a small error in the grinding of the primary mirror (about one-fiftieth of a millimeter) caused this error. This error could have potentially rendered Hubble an ineffective tool, but fortunately, Hubble was in an accessible orbit, and at that time, space shuttles were still operating in Earth orbit. After various assessments and proposals, engineers successfully designed a tool that could resolve this defect. The construction and preparation of this tool took about three years until, in 1993, the space shuttle Endeavour set off to meet the Hubble Space Telescope. With the installation of this tool and some other updates, once again anticipation and anxiety among scientists peaked, and when the first images arrived on Earth, it was once again shouts of wonder that filled the control room; this time, however, not due to a problem with the images but because of the stunning views that Hubble had presented before our eyes. Since its inception, the Hubble Space Telescope has contributed to thousands of astronomical discoveries and has expanded our view of the universe with images of the cosmos's depths, known as Hubble's deep and ultra-deep images. Few tools in the history of astronomy have played such a role in the advancement of science. However, like any other tool, Hubble has gradually worn out over time and required repairs. In 1997, 1999, and 2009, missions were conducted to repair and update Hubble's instruments, but when the space shuttle Columbia was lost on its return to Earth and the shuttle program faced risks, Hubble's future was also jeopardized. NASA decided to allocate several flights solely to complete the International Space Station, given the irreparable flaw in the shuttles' thermal shields, and then retire the shuttle program. The relentless efforts of the astronomical community persuaded NASA to add a Hubble repair mission to the final flights of the shuttles; a mission that took place in 2009, after which the era of space shuttles also came to an end. Now, more than 34 years have passed since Hubble went into space. Hubble uses two sets of three gyroscopes to track its target and adjust its orientation for new objectives. Recently, one set of these gyroscopes failed, and Hubble relied on the three remaining gyroscopes, but in recent months, with the repeated failure of one of these instruments, Hubble has frequently entered Safe Mode. After repeated assessments, engineers have suggested that to extend Hubble's operational life, navigation and orientation should be managed by only one gyroscope, keeping the other two as backups to replace one with another in case of failure. However, this means that Hubble will no longer be able to observe and track objects closer than Mars's orbit. This tool also has limitations on exposure time and requires more time to point toward new targets. Hubble will ultimately cast its gaze into the depths of the universe for the last time in the coming years and will forever close its eyes to the world. Although there are no plans for its repair, there may be an attempt to return it to Earth safely. However, Hubble's name will remain in history as a tool that expanded our view of the universe, alongside instruments like the Galileo telescope. The James Webb Space Telescope, although observing the universe with greater power and capability, is not a replacement for Hubble. There are still thousands of unanswered questions awaiting data from our space instruments, and there are still thousands of questions that we are even unaware of, waiting to reveal themselves. The Whirlpool Galaxy, a classic spiral galaxy, is located 30 million light-years from Earth and spans 60 thousand light-years; this is a digital composite image of a ground-based telescope image combined with an image sent by Hubble.