Hubble Space Telescope still going strong after 30 years in space
Thirty years ago Friday, the Hubble Space Telescope was launched aboard the shuttle Discovery with a famously flawed mirror, the opening chapter in an improbable saga of redemption and scientific discovery that revolutionized humanity's view of the cosmos with jaw-dropping images now familiar to millions.
The list of Hubble's achievements is both long and stunning, everything from proving the existence of supermassive black holes to pinning down the age of the universe to within a few percent.
Hubble's exquisite vision has allowed astronomers to study the chemical make up of exoplanet atmospheres, to capture flyby-class views of planets in Earth's solar system and to collect mind-bending "deep field" images showing the first galaxies coalescing in the wake of the big bang.
Adam Riess shared a Nobel Prize for Hubble research that helped confirm the expansion of the universe is accelerating, not slowing down or flattening out as expected, one of Hubble's most profound results. He's using the telescope now to help resolve discrepancies in that expansion rate, high-stakes research that could reshape the theoretical underpinnings of cosmology.
"Obviously there will be other telescopes, but I don't know if there's going to be a telescope that takes us as far from sort of where we were to where we end up," Riess said in an interview.
"It's almost like when (sailors first) circumnavigated the globe, there's only sort of one time that you get to open up that much unexplored territory. Hubble arrived at a time when we had never seen the universe with that kind of crisp resolution and able to see so far out. The new telescopes will really help follow up on so much of what we learned from Hubble. It's just that Hubble was such a game changer."
James Fanson, project manager of the Giant Magellan Telescope, one of the huge new ground-based observatories now under development, said in a statement that Hubble had revolutionized astronomy "in the same way Galileo's telescope did 400 years ago when first turned to the heavens."
"Hubble's images reached the level of art, and its discoveries touched the imagination of ordinary people around the world. Hubble became the 'people's telescope,' and it will always have a cherished place in our history and culture."
NASA unveiled a 30th anniversary photo from Hubble on Friday as part of a relatively subdued celebration. Because of coronavirus travel restrictions, a variety of events marking the anniversary have been put on hold.
"We'll unveil the image for our staff just as it's being unveiled for everybody else around the world," said Ken Sembach, director of the Space Telescope Science Institute. "And it is spectacular. We're going to be doing that virtually, though. We had all kinds of events planned around the world and with COVID, it's just going to be different."
Many of Hubble's most spectacular discoveries were unimagined when the telescope was launched on April 24, 1990, especially after engineers discovered its supposedly near-perfect 94.5-inch primary mirror was perfectly flawed, a victim of spherical aberration that prevented the telescope from bringing starlight to a sharp focus.
Seven years behind schedule and some 400 percent over budget, Hubble had been launched to great fanfare and promises from NASA that it would take astronomy to new heights. Spherical aberration was an utterly gut-wrenching, almost impossible-to-believe defect, caused by an oversight during the mirror's fabrication.
The dismal news was announced on June 27, 1990, and Hubble quickly became the butt of jokes on late-night television and the subject of heated congressional hearings, including one two days later in which Maryland Senator Barbara Mikulski, a long-time NASA supporter whose district included the Goddard Space Flight Center, famously referred to Hubble as a "techno turkey."
"What does this mean for the rest of the things you want to do?" she was quoted by UPI. "Are we going to keep ending up with techno turkeys? I think this has seriously hurt the credibility of NASA when they've had so much time and enough money to get it right."
Said now-retired Hubble project scientist Ed Weiler, recalling the sense of despair that many felt: "We went from the top of Mount Everest to the bottom of Death Valley."
"You know, people would stop me, pushing my little girl around the block, saying 'I'm so so sorry you have to work on that national disgrace'," he said. "It's great when your neighbors tell you that, right?"
But engineers quickly figured out a way to correct Hubble's blurry vision: installing a new camera, one that Weiler had recommended earlier, with relay mirrors ground to prescriptions that would exactly counteract the primary mirror's aberration.
Building on that idea, another device, known as COSTAR, was designed to direct corrected light into Hubble's other instruments.
During a make-or-break December 1993 shuttle servicing mission, the new Wide Field Planetary Camera 2 and COSTAR were installed by spacewalking astronauts. They also replaced Hubble's solar panels and other critical components.
The following January, NASA unveiled the results during a news conference at Goddard: crystal-clear views of a galaxy known as M-100 that left no doubt Hubble was finally ready for prime time. Before the briefing began, Weiler showed Mikulski the pictures.
"I had them all laid out," he said. "I had a picture of M-100 taken with spherical aberration, taken from the ground and then taken from Hubble, all three together. And she walked in. She looked at them and she said, 'My God, it's like putting on my glasses.' I'll never forget that moment."
NASA would go on to launch four more servicing missions, installing new, state-of-the-art instruments and replacing aging components like critical fine guidance sensors and gyroscopes, which move the telescope from target to target and then lock-on with rock-solid stability for detailed observations.
Eleven years after NASA's fifth and final servicing mission in May 2009, Hubble is still going strong. The Space Telescope Science Institute still receives some 1,200 observing proposals each year, of which only about 250 can be accommodated.
"Hubble's doing extremely well," Sembach said. "It's still operating at peak performance. That means that it's continuing to have a full schedule of observations. In fact, the observatory's probably as efficient right now in conducting science as it's ever been. All the instruments are working really well."
He said Hubble's subsystems also are behaving "reasonably well."
"So good power, good pointing, good communications, good storage," he said. "The gyros are operating better than we had expected. There are some little issues here and there, but we're dealing with those with flight software changes and so forth. So right now it's actually looking really good."
The gyros are critical to Hubble's longevity. The telescope was launched with six ultra-stable gyroscopes, but only three at a time are needed for normal operation. During the final servicing mission, all six were replaced but since then, three have failed, leaving Hubble without any redundancy.
"The main issue that we're seeing in one of them ... is the bias rate," Sembach said. "Every gyro has a little drift over time, it drifts a little bit from the position it thinks it's pointing to the position it senses. And so that's something that we correct all the time.
"In one case, one of the gyros, that bias level is getting up to levels where it's getting a little bit more flaky at times, which means we occasionally lose a guide star acquisition, or the pointing isn't quite as good as we would have liked. That's still a small number of cases. And the bias levels that we see are still within the range of being correct."
To be on the safe side, engineers have developed software that would allow Hubble to operate with just two gyros or even one. The downside is the telescope could only reach targets in about half the sky at any given time instead of 85% or more with all three gyros.
"The thought would be, at least at the moment, that if one of those three gyros fails, we would, in fact, drop to one gyro control and turn the other one off to preserve its lifetime if we thought that that was the right thing to do at the time."
Based on Hubble's current health, he added, "we should have another good five years in it. And maybe longer. I would, for one, never bet against Hubble."
Neither would Riess.
"You should never count out Hubble, that's what I've learned," Riess said. "We're pretty optimistic we can get five more years. But as I said, I wouldn't count it out. If we come back in, you know, 10 years or 15 years and we found a way to keep it going in some useful way, that wouldn't shock me either."
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