April 25, 2015 marks 25 years since the Hubble Space Telescope was released from the Space Shuttle cargo bay to become a free-flying mini-moon of Earth. Since that time, this amazing spacecraft has logged some 5 billion kilometers (3 billion miles) in its orbit around Earth. But if that distance sounds far, it is nothing compared to how much farther Hubble has seen. If Hubble had traveled the 5-billion-kilometer distance straight outward into space, it would now take its light a little more than 4 ½ hours to travel back to Earth. But the light that Hubble has recorded from some distant galaxies has traveled through space for more than 12 billion years to reach us. Hubble has dramatically enhanced our view of the universe, both in space and in time.
Hubble's story is being retold in many media retrospectives, so I'll give only the briefest overview here. From the time Galileo first turned his telescope to the sky in 1609 until the launch of Hubble, nearly all astronomical observations had been conducted with telescopes on the ground. (Yes, there were a number of space observatories prior to Hubble, but none that could take visible light pictures with anywhere near the same power.) While these telescopes had taught us much about the universe, astronomers had long recognized that ground-based telescopes suffered from two major limitations:
- Because ground-based telescopes peer through Earth's turbulent atmosphere, their images tend to be blurred; in essence, it is the same effect that makes stars twinkle in the night sky, even though the stars themselves are steady sources of light.
- Much of the light that comes to us from the cosmos is in forms that our eyes cannot see, such as infrared and ultraviolet light, most of this light cannot penetrate Earth's atmosphere, rendering it impossible for ground-based telescopes to observe.
Hubble's placement above Earth's atmosphere overcomes both limitations, allowing it to obtain crystal clear images of the universe in visible, infrared, and ultraviolet light.
The idea for Hubble is usually traced back to astronomer Lyman Spitzer, who pushed for a space telescope beginning in 1946. (Others had suggested space telescopes earlier, but not with the same level of detail.) Congress approved the project in 1977, in part to provide a mission for the new Space Shuttle, which could deliver it to space and allow astronauts to service it. Its launch date was set back more than 3 years by the 1986 loss of the Space Shuttle Challenger. It finally lifted off in the Space Shuttle Discovery on April 24, 1990, which released it into space the next day.
The telescope takes its name from Edwin Hubble, a giant of astronomy who, in 1923, discovered the first definitive proof that the Milky Way is just one of billions of galaxies in the universe. This fact is worth brief elaboration, since it surprises many people today, when spectacular telescopic photos like those form the Hubble Space Telescope make it seem obvious that there are countless galaxies beyond our own. At the time, however, telescopes showed other galaxies only as rather fuzzy blobs of light, and until Edwin Hubble's work, no one had been able to determine for certain whether those blobs were distant collections of stars or relatively nearby clouds of gas. The latter possibility implied that the Milky Way might represent the entire universe, so in proving this possibility to be incorrect, Hubble effectively made us realize that the universe was some 100 billion times larger than we had known before. He culminated this work with his 1929 discovery that our entire universe is expanding. In this sense, naming the Hubble Space Telescope for Mr. Hubble not only honored his achievements but also hinted at the way it would expand the understanding of the universe that Hubble had first offered us.
Of course, there's another aspect to the Hubble Space Telescope story, and that is one of resilience and perseverance. Shortly after its launch, astronomers were dismayed to find that it was not taking the clear images that had been expected. With a thorough investigation that would make Sherlock Holmes proud, scientists and engineers traced the problem to a flaw in the shape of the telescope's primary mirror - the part of the telescope that collects all the light from distant objects. Fortunately, the telescope's shape proved to be "perfectly flawed," in the sense that it had been made perfectly but to the wrong shape. As a result, scientists and engineers were able to design mirrors and lenses that could be attached to telescope instruments and reverse the effects of the flaw; in essence, providing "eyeglasses" for the world's most powerful telescope. These corrective lenses were first installed in 1993, and from that time on the telescope has been able to fulfill its full potential.
This is where my personal reflections come in. I had the great privilege of being hired to work at NASA Headquarters shortly after the mirror flaw was discovered. Although I had absolutely nothing to do with any of the work that made the fix possible -- my job was to create ways of leveraging astronomy missions for education and outreach -- I in essence had a front-row seat to everything that transpired. The dedication and integrity shown by scientists, engineers, and, yes, "bureaucrats" who were typically in the office before 7am and working late into the evening every day, was something to behold. There are far too many unsung heroes to mention here, but I'll call attention to one: Charlie Pellerin, the Director of Astrophysics at the time. As the leader of the Division that had launched the flawed mirror, Dr. Pellerin was on the hot seat, called often to testify before Congress and speak to the news media. Yet Charlie managed always to maintain focus on discovering the source of the problem (which proved to have been due to the contractor, not to NASA's oversight) and finding the fix, and I believe his leadership was a key part of the reason that the Hubble Space Telescope ultimately succeeded.
How successful has it been? Shortly before Hubble was launched, and before I was officially hired on at NASA, I was asked to review a short video that sought to explain the mission. It was very well done, but I had one complaint: While I was as confident at the time as anyone that Hubble would prove to be a great observatory, I thought the video had gone over the top in claiming that it would be as revolutionary in our time as Galileo's telescope had been in his. My caution seemed especially well-warranted when the mirror flaw was discovered. But then it was fixed... and I can now admit that I was wrong. Centuries from now, when historians look back at the discoveries that have shaped our view of the universe, I believe that the Hubble Space Telescope will have earned its place.