Fwd: Celebrating 25 Years of Hubble Science

Sent from my iPad

Begin forwarded message:

From: "Gary Johnson" <gjohnson144@comcast.net>
Date: April 27, 2015 at 10:12:16 AM CDT
To: "Gary Johnson" <gjohnson144@comcast.net>
Subject: FW: Celebrating 25 Years of Hubble Science

 

 

AmericaSpace

For a nation that explores
April 24th, 2015

Shedding New Light On the Solar System: Celebrating 25 Years of Hubble Science (Part 1)

By Leonidas Papadopoulos

A photograph of the Hubble Space Telescope. taken by the crew of the STS-109 mission, following the successful completion of the fourth Hubble servicing mission in 2002. The iconic orbiting observatory, which celebrates 25 years of successful operation this month, has completely revolutionised our view of the Cosmos. Image Credit: NASA/STScI

"All truths are easy to understand once they are discovered; the point is to discover them."

Galileo Galilei (1564-1642)

 

In the words of a famous Chinese proverb, "The journey of a thousand miles begins with one step." Likewise, most of the great intellectual and spiritual revolutions and paradigm shifts that have shaped the course of human history were characterised by small and humble beginnings, the importance of which was originally seen as inconsequential at the time. Similarly, the history of physics and astronomy is also characterised by events that have forever changed the way we view the world, from Isaac Newton's formulation of the laws of motion and Galileo's first telescopic observations of the night sky in the 17th century, to Albert Einstein's development of the theories of special and general relativity and Edwin Hubble's discoveries about the scale and expansion of the Universe in the early 20th century.

A similar widening of humanity's perception of the Universe has also taken place in recent years, courtesy of NASA's Hubble Space Telescope. The iconic space observatory, which celebrates 25 years in orbit this month, has made more than one million observations of the Universe to date, which have helped scientists and non-scientists alike to truly visualise the notion of the infinity of space and time, like no other instrument before it. The cutting-edge science that has been conducted by the orbiting observatory during this time has exceeded all expectations, resulting in the publication of more than 12,700 papers in the scientific literature worldwide, which have completely transformed almost every research area of cosmology astronomy and astrophysics. At the same time, Hubble has returned images of the Cosmos of unparalleled aesthetic beauty that have been the wallpapers of choice on the computer screens of millions of people around the world, helping to also change the public's view of the Universe in the process. "Hubble has in so many ways completely revolutionised our understanding of the Universe," remarked Dr. Amber Straughn, an Astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., during a recent commemorative talk at the Museum of Flight in Washington, for Hubble's upcoming 25th anniversary. "It changed the way that we as astronomers understand space. But even more than that, I think on a more profound level it changed the way that humanity thinks about space. Before Hubble, people thought of space as [being] dark and void. After Hubble, people think of space as [being] colorful and beautiful. And I think that this very subtle shift in how people generally think about space is really profound and it speaks to the significance that Hubble has had on our culture."

An infographic showing several of the Hubble Space Telescope's impressive statistics. Image Credit: NASA/KSC/Spaceport Magazine

The full breadth of Hubble's observations of the Cosmos would require many volumes in order to be adequately presented. Even though this exceeds by far the scope of just one article, this AmericaSpace series nevertheless aims to present some of the most important cosmic discoveries ever made by the Hubble space telescope, as well as the iconic images that accompany them, in order of increasing distance from Earth.

New Views of Familiar Planetary Vistas

A composite assembled from separate images of Jupiter and comet Shoemaker-Levy 9, that were taken with the Hubble Space Telescope in July 1994, as the comet was about to impact the giant planet. The dark spot on the planet's disc is the shadow of the inner moon lo. Image Credit: NASA, ESA, H. Weaver & E. Smith (STScI) and J. Trauger & R. Evans (Jet Propulsion Laboratory)

The start of 1994 heralded a new beginning for the Hubble Space Telescope as well as for astronomy in general. Having already been repaired in orbit by the crew of the STS-61 mission in December of the previous year, which had triumphantly succeeded in correcting its originally impaired vision, the orbiting observatory had already started to send back images of deep space that had all the clarity and resolution that astronomers had hoped for. Nevertheless, during the summer of 1994 scientists and the public alike were treated to a cosmic fireworks display, the likes of which had never been observed before in human history. Comet Shoemaker-Levy 9, which had been discovered several months prior the launch of the first Hubble servicing mission, was found to be on a collision course with Jupiter, giving astronomers a first-rate chance to witness the event live as it progressed. Having been broken up into a total of 21 large fragments by the massive gravity of the gas giant planet, Shoemaker-Levy 9 finally impacted piece by piece onto the cloud tops of Jupiter's southern hemisphere between July 16 and July 22, 1994, releasing the energy equivalent of several million megatons of TNT in the process.

Hubble's Wide Field Planetary Camera-2 was able to make detailed observations of the planet-sized impact sites in optical and ultraviolet wavelengths, providing scientists with their first direct measurements of the planet's atmospheric composition below the visible cloud tops. Spectroscopic analysis of the results revealed the presence of molecules like sulfur, carbon disulfide, hydrogen sulfide, and ammonia, while also finding that Jupiter's atmospheric abundances of molecules like water and hydroxyl were much lower than expected, contrary to the predictions of planetary scientists. Furthermore, Hubble's Faint Object Spectrograph recorded dramatic changes in the planet's massive magnetosphere while the latter was penetrated by the comet's fragments, resulting in large electromagnetic disturbances along Jupiter's magnetic field lines which temporarily generated unexpectedly bright aurorae. But perhaps one of the more important lessons to be learned from Shoemaker-Levy 9's impact on Jupiter was the role that asteroids and comets play in the evolution of planetary systems, as both the carriers of life and the bringers of doom. "More than anything else, this comet taught us about the role that impacts have played in the history of the Solar System," David Levy, co-discoverer of Shoemaker-Levy 9, would later write for Sky & Telescope. "Comets have been shown to contain the building blocks of life, particularly "CHON" particles — consisting of carbon, hydrogen, oxygen, and nitrogen — that form the alphabet of life."

Cosmic collisions aside, Hubble has conducted a whole list of revolutionising studies of Jupiter as well as of the entire Jovian system, even from a distance of more than 500 million km away, including the giant planet's powerful auroras, its rings and atmospheric circulation, and its trademark Great Red Spot. The latter is a gigantic high-pressure, anti-cyclonic storm three times the size of Earth that has been raging for more than 300 years at the planet's southern hemisphere. A series of observations with Hubble's Wide Field Camera 3 in recent years have provided high-resolution images of Jupiter which confirmed scientists' previous suspicions that the Great Red Spot is getting smaller and more circular with time. At the same time, a white storm that had been previously observed at the same latitudes by astronomers on Earth suddenly turned red in 2006, only to develop a similar shape and structure to the Great Red Spot, albeit smaller in size. This new anti-cyclonic feature, affectionately named "Red Spot Jr." or "the Little Red Spot," has been gaining in strength and size ever since, while its bigger counterpart is steadily shrinking, leaving astronomers perplexed as to the reason why these atmospheric features can last so long, or why their size is constantly changing. "No one is certain what gives these storms their red color," had co-written Dr. Amy Simon in 2008, a Senior Scientist for Planetary Atmospheres Research at NASA's Goddard Space Flight Center in Greenbelt, MD, for the agency's Annual Hubble Year In Review. "One theory is that the storms are so powerful that they dredge up gases or particulates from deep in Jupiter's atmosphere to higher altitudes, where ultraviolet radiation disassociates the elements within their molecules. Subsequent chemical reactions may lead to the red color."

"In terms of what does that mean, is [the Great Red Spot] going to go away? Well, part of the problem is that we don't understand what is it that sustains it in the first place," commented Simon during a Google Hangout last year, following the release of Hubble's observations of the phenomenon.

A series of images of Jupiter's Great Red Spot taken by the Hubble Space Telescope over a span of 20 years, showing how the planet's trademark atmospheric feature has decreased in size over the years
Image Credit: NASA/ESA

Yet, what could possibly be described as Hubble's most exciting observations of the whole Jovian system were those regarding the planet's four Galilean satellites. Not long after the space telescope's optics had been corrected back in the 1990s, it provided fascinating views of new eruptions on the volcanic moon Io, detected ozone molecules on Ganymede—which provided evidence that more interesting oxygen-based chemical reactions could be taking place on the moon's surface—and identified the presence of an extremely tenuous atmosphere of molecular oxygen around Europa, another fascinating Jovian moon which is thought to harbor an underground global ocean of liquid water. This prospect was strengthened considerably in late 2013, when Hubble detected traces of water vapor coming off Europa's south polar regions, which scientists interpreted as evidence for the possible existence of water plumes, not unlike those seen on Saturn's moon Enceladus. As if not wanting to be outdone by its celestial sibling, Ganymede revealed tantalising hints of its own potential habitability to Hubble, when the latter uncovered evidence for the existence of a saltwater ocean below the moon's surface. Such findings only bolster the case for the presence of potentially habitable environments and even life in the cold regions of the outer Solar System, an expanse which was previously considered of being utterly hostile to biology. "NASA science activities have provided a wave of amazing findings related to water in recent years that inspire us to continue investigating our origins and the fascinating possibilities for other worlds, and life, in the Universe," says Ellen Stofan, chief scientist for the space agency. "In our lifetime, we may very well finally answer whether we are alone in the Solar System and beyond."

The Majesty of A Ringed World

We may have become accustomed nowadays on the constant stream of spectacular images of the magnificent Saturn and its moons, courtesy of NASA's Cassini spacecraft, but the Hubble space telescope definitely has its share of important observations of the sixth planet from the Sun as well. Even before the first Hubble servicing mission in 1993, the orbiting telescope was already providing scientists with detailed views of Saturn's rings and various atmospheric features, long before Cassini had reached the ringed world. Just a year after it was launched, Hubble had detected a white planet-wide storm covering Saturn's entire equatorial region, an atmospheric phenomenon which repeats itself approximately every 29 years, when the planet's northern hemisphere enters summer. This gigantic storm system, better known as the Great White Spot, was briefly imaged again in 1994 with Hubble's corrected optical system, allowing scientists to discern the storm's intricate influences in the surrounding atmospheric layers.

A breathtaking Hubble image of Saturn in ultraviolet light, showing the planet's southern hemisphere and the southern face of its rings. Image Credit: NASA/ESA and E. Karkoschka (University of Arizona)

Hubble's observations of Saturn's aurorae have proved to be of equal importance to planetary scientists, allowing them to monitor them extensively in ultraviolet wavelengths during the course of more than a half Saturnian year. These studies revealed that Saturn's aurorae share several similarities with those of other planets in the Solar System, yet are also quite unique at the same time, exhibiting features that are seen nowhere else in the Solar System. More recent observations conducted during the last couple of years returned stunning images of the auroral activity on the ringed world, allowing scientists to confirm a long-held theory which posited that Saturn's bright aurorae are mostly driven by the collapse of the planet's magneto-tail, when powerful eruptions from the Sun slam onto Saturn's magnetosphere. "These [latest] images are spectacular and dynamic, because the auroras are jumping around so quickly," said Dr Jonathan Nichols, a planetary scientist at the University of Leicester's Department of Physics and Astronomy in the UK, following the publication in 2014 of the first results of a dedicated Hubble three-year observing campaign of Saturn. "The key difference about this work is that it is the first time the Hubble has been able to see the northern auroras so clearly. Our observations show a burst of auroras that are moving very, very quickly across the polar region of the planet. We can see that the magneto-tail is undergoing huge turmoil and reconfiguration, caused by buffering from solar wind. It's the smoking gun that shows us that the tail is collapsing."

Even though NASA's unmanned Galileo and Cassini space probes have returned a treasure trove of data while orbiting Jupiter and Saturn respectively, the Hubble space telescope has nevertheless kept its rightful place as a leading observatory in the field of planetary science. During the last 25 years, it has allowed astronomers to considerably advance our knowledge and overall understanding of the Solar System, in ways never dreamed of when originally designed in the 1970s and '80s. "During the run up to the [Hubble launch] mission [in 1990], there was a sense certainly among my fellow crew members and me that Hubble was going to be something special," NASA's Administrator Charles Bolden told AmericaSpace's Emily Carney, while commemorating Hubble's 25 years of unprecedented, cutting-edge science. "We didn't know, however, how special—frankly, I'm not sure anyone did. By any measure Hubble has exceeded even our wildest expectations."

This fact became readily evident with Hubble's exploration of the vast expanses of the outer Solar System beyond the orbit of Saturn.

 

Copyright © 2015 AmericaSpace - All Rights Reserved

 

---

 

 

AmericaSpace

For a nation that explores
April 25th, 2015 

'Somebody Get a Camera': 25 Years Since the Launch of Hubble (Part 2)

By Ben Evans

Twenty-five years after its April 1990 launch, the iconic Hubble Space Telescope remains functional. Photo Credit: NASA

Twenty-five years ago, yesterday, on 24 April 1990, one of the most important missions in the annals of scientific discovery got underway, with the launch of NASA's Hubble Space Telescope. As described in yesterday's AmericaSpace history article, this $1.5 billion observatory—with its five instruments and finely ground mirrors—promised to revolutionize astronomy. It would peer deeper into the cosmos than ever before, unhindered by the distorting effects of Earth's atmosphere. In time, it would examine "nurseries" of young stars and "graveyards" of ancient ones, would study galaxies in unprecedented depth, would watch as a comet smashed into Jupiter, would trace violent storms on Uranus and Neptune, and would create maps of far-off Pluto. And 25 years ago, today, on 25 April 1990, the telescope was released from the payload bay of Shuttle Discovery by the crew of STS-31. However, its childhood was marred by technical difficulty, which made it the butt of cruel humor and an object of criticism from NASA's opponents.

None of this could have been further from anyone's mind on 10 April 1990, as controllers counted down toward the launch of the telescope on STS-31. Aboard Shuttle Discovery were five astronauts—Commander Loren Shriver, Bruce McCandless, Steve Hawley, Kathy Sullivan, and the man who would one day become NASA's first African-American Administrator, Charlie Bolden—who were tasked with the enormous responsibility of getting this gigantic icon of astronomy into the highest orbit ever attained by the shuttle, some 380 miles (610 km) above Earth. However, the 10th was not to be their day. The countdown clock stopped at T-4 minutes, when abnormal pressures and turbine speeds were detected in one of Discovery's Auxiliary Power Units. Two weeks later, on the 24th, they were back for another try. This time, the clock halted at T-31 seconds, just before the on-board computers assumed primary control, due to glitch with a liquid oxygen fill and drain valve. When this had been rectified, STS-31 roared into space. "Our window on the Universe!" came the call from the launch commentator, as Discovery speared toward orbit, atop a pillar of golden flame.

Within hours, the shuttle's payload bay doors were open, revealing the monster telescope in all its splendour. More than 43 feet (13 meters) long, glistening with shiny insulation and weighing an impressive 24,250 pounds (11,000 kg), Hubble filled the bay and left the astronauts awestruck. In fact, its aluminum coating was so reflective that it blazed brightly in the harsh, unfiltered sunlight … so brightly that Steve Hawley would later recommend that future servicing missions should rendezvous with the telescope during orbital darkness to avoid momentarily blinding the astronauts or their cameras.

With the grandeur of Earth, from the highest orbit yet attained by the shuttle, providing a spectacular backdrop, the crew of STS-31 prepares to deploy Hubble on 25 April 1990. Photo Credit: NASA

Deployment was slated to occur on the second day of the mission, 25 April 1990, and the STS-31 crew received special wake-up music in the form of the song "Space Is Our World," written by a Houston-based band, Private Numbers.

Later that morning, Hawley gingerly grappled the massive payload and positioned it above the bay, with its large aperture door facing forward. Its two high-gain antennas were released, springing "downward" and "outward," and the next step was to open British Aerospace's solar arrays, which would unfurl like kitchen roller blinds. The first array came out perfectly, and Shriver reflected that it was incredible to behold. The second array was more problematic. It began to unroll for a few centimetres, then abruptly stopped. Everyone's heart skipped a beat. Time was of the essence. After cutting umbilical power to the telescope, the astronauts had just two hours on internal batteries to get the arrays open and enable Hubble to draw its own electricity. If that did not happen, the batteries would die … and so would the telescope. The worry went up in notches with the realization that Hubble might be in severe difficulty.

An EVA repair seemed the only solution. Having reduced Discovery's cabin pressure the previous night, McCandless and Sullivan were already downstairs, clad in their space suits, in the airlock, with tools, ready to go outside. McCandless was convinced that he knew the source of the problem: a glitch with a tension monitoring module. This was a unit of software to detect any excessive strain on the array and prevent it from tearing or binding. It would stop the array-deployment process and the spacewalkers would then have to fix it manually. To give them more time, they had partially completed their pre-EVA procedures before Hubble was grappled. "What's left," Sullivan told the NASA oral historian, "is to button up the suit, breathe 40 minutes of pure oxygen, close the hatch, depress and get outside."

It was a double-edged sword, for despite having a spacewalk it also meant that Sullivan's other task of photographing the deployment would be missed. Before launch, she had resolved to literally "wallpaper the telescope with photos" … in fact, she wanted a cover shot on Aviation Week. Now, after working for five years on Hubble, she was locked up in the airlock and might not even see the instant of its release. With only minutes remaining before she and McCandless would have been directed to fully depressurize the airlock, Mission Control told them that the problem was an erroneous software indication … from the tension monitoring module. An engineer requested permission to command the module to "No-Op" ("No Operation", effectively taking it "out of the loop") and was certain that this would enable the stubborn second array to unfurl. STS-31 Flight Director Bill Reeves concurred and Capcom Story Musgrave radioed up the news: Hawley was to orient Hubble in a ready-to-deploy attitude and if the attempt to "No-Op" worked, the array would likely start unfurling immediately and they would have to release the telescope as quickly as possible.

Hubble's solar arrays, in the process of deployment. Photo Credit: NASA

It worked.

Charlie Bolden was astounded, but McCandless offered a wizened grin. He had worked on Hubble for so long that he knew, instinctively, what had caused the problem.

Steve Hawley's primary concern during the deployment, aside from the array, was the very remote chance that Discovery's Canadian-built Remote Manipulator System (RMS) mechanical arm might fail. The joints of the arm were intentionally limited in terms of their speed, thereby offering him some margin to respond to contingencies, and that meant that the motion he could command was restricted. As he lifted Hubble, it "wobbled"—a lot more than the simulator had taught him that it should—and not until after landing did he realize that the signal "noise" in the joints contributed to random imparted motions. In his post-mission debriefings, he recommended that future simulations should take joint noise into account … a recommendation which would prove hugely beneficial for Swiss astronaut Claude Nicollier, who would grapple Hubble on the first servicing mission in December 1993 and for Hawley himself, who would fly the second in February 1997.

Charlie Bolden was not immune to the irony that the crew had actually practiced a solar array deployment failure during their last integrated simulation, shortly before launch. In that instance, McCandless and Sullivan had manually wound out the array, although they knew that doing such an action for real had the potential to severely damage the telescope. "Once you did that," Bolden said, "it took it out of its automatic mode and it would no longer be able to take care of itself … sort of like taking a baby from the womb, putting it on a respirator and putting it in a position where the rest of its life it would need something. That was what that would have meant for Hubble … until you send another crew up and put on another set of solar arrays and reset the clock."

Disappointment at being unable to perform an EVA extended a little further when McCandless and Sullivan were unable to see the moment of deployment. Bolden certainly felt for them, still cooped up in the airlock. "So we deploy Hubble, coming off the Pacific Ocean, across the west coast of South America," he told the NASA oral historian, "and it's just the most beautiful thing you can imagine. It comes off the end of the arm and down. We're looking at the Andes Mountains and it goes right across the coast between Bolivia and Venezuela." Shortly afterward, he and Shriver pulsed Discovery's thrusters, twice, to raise their orbit slightly, causing them to fall steadily "behind" the telescope. As Hubble drifted serenely away, the three men on the flight deck gaped at what they were seeing. Then, all of a sudden, and in unison, they all barked: "Camera! Somebody get a camera!"

The STS-31 crew (from left) consisted of Charlie Bolden, Steve Hawley, Loren Shriver, Bruce McCandless, and Kathy Sullivan. Photo Credit: NASA

Bolden helped to save the day in terms of the photography. An IMAX large-format camera was already filming the deployment from the rear of the payload bay, and Bolden also acquired some spectacular footage from the cabin, with the hand-held IMAX. Having sealed McCandless and Sullivan in the airlock, he shot a length of film as he floated upstairs to the flight deck, focusing firstly on Shriver at the orbiter's controls, then on Hawley at the RMS controls, and then through the windows to reveal the Hubble Space Telescope in all its magnificence. It was not like a "normal" camera, where it was possible to see what was occurring through the lens; rather, Bolden had nothing to gauge whether he was doing the right thing. After the flight, his biggest surprise was not just that the camera worked, but that it also stayed in focus. Later, IMAX would include Bolden's imagery as part of its Blue Planet and Destiny in Space documentaries.

Four days later, on 29 April 1990, Shriver and Bolden brought Discovery smoothly onto the concrete runway at Edwards Air Force Base in California's Mojave Desert, capping a mission which promised to open a new set of eyes on the Universe. In the first few weeks, Hubble's early problems seemed benign: a few communications glitches, drifting star trackers, and snagged coaxial cables were part and parcel in the process of wringing out a new spacecraft. More serious concerns arose when temperature changes bent materials in the solar arrays' booms, the effect of which was magnified by the orientation mechanism in such a way that it physically "bounced" the whole telescope. The result was a "jittering" in Hubble's images and, since the booms only stabilized in the final few minutes of orbital daylight, the pointing system was only able to meet its design specifications for a fraction of each orbit. NASA engineers worked with their counterparts at Lockheed to change the control program in Hubble's computer and successfully counteracted the vibrations. On 21 May 1990, the telescope returned its first images of a double star in the Carina system, and these were lauded as being much clearer than were achievable with ground-based instruments.

Four weeks later, calamity befell the mission. On 24 June Hubble failed a focusing test. Its secondary mirror had been adjusted to focus the incoming light from a celestial source, but a fuzzy ring—like a halo—encircled even its best images, creating a blur. Additional tests revealed that the telescope was suffering from a condition known as a "spherical aberration" in its primary mirror. In essence, Perkin-Elmer, had ground it to the wrong specification, removing too much glass and polishing it too flat … by a mere fiftieth of the width of a human hair. The consequence was that Hubble was unable to acquire sharp images. With mounting horror, NASA realized that its attempts to sell its scientific showpiece on the basis of its ability to see further into the cosmos than ever before, with unprecedented clarity, now became increasingly hollow. The promised white knight of astronomy was turning instead into a white elephant.

The STS-31 crew patch highlighted the expectation of astronomical discovery from Hubble. Image Credit: NASA

Even Hubble's chief scientist, Ed Weiler, admitted that its capabilities were comparable only to "a very good ground telescope on a very good night." The politicians were quick to vent their fury. Senator Barbara Mikulski from Maryland, exploded that Hubble was "a techno-turkey" and wasted taxpayers' money. Meanwhile, Senator Al Gore of Tennessee—later vice president during the Clinton administration—observed that, for the second time in less than half a decade, NASA's quality control shortcomings had been exposed. The press had a field day. Particular venom was leveled at the fact that NASA had accepted Perkin-Elmer's $64.2 million bid to build the mirror and rejected a more expensive, though more thorough, $99.8 million proposal from Eastman Kodak and defence contractor Itek. On 28 July, the New York Times reported that Kodak-Itek's bid would have subjected the mirror to two independent checks of its grinding and polishing accuracy. Almost certainly, this would have caught the error before launch.

NASA responded that, with 20-20 hindsight, it would have cost $100 million to incorporate additional tests and independent checks of the telescope optics into the Perkin-Elmer contract, but the effect upon the general public was the same. The space agency was rendered a laughing-stock on late-night TV talk shows. David Letterman compiled a pejorative list of "Top Ten Hubble Excuses," whilst others criticized NASA for its mismanagement of both the Hubble development and the Solid Rocket Boosters (SRBs) which doomed Challenger. Several space policy analysts, including John Logsdon, noted that attitudes had changed from the 1960s, in which problems were anticipated and incorporated into planning, to the late 1970s and 1980s when little effort was made to prepare for unforeseen obstacles.

In early July 1990, NASA established an investigating committee, chaired by Lew Allen, the head of the Jet Propulsion Laboratory. His report—published the following November—harshly criticized the incorrect assembly of the "reflective null corrector," an optical device used to determine the figure of Hubble's mirror. The location of a lens in the device was improperly measured and the null corrector guided the polisher to shape a perfectly smooth mirror … with the wrong curvature. Analysis revealed that the curvature flaw in the primary mirror exactly matched the flaw in the null corrector. A second null corrector, made only with lenses, was also built to measure the vertex radius of the finished mirror. It, too, clearly identified an error in the primary mirror. However, neither warning sign was heeded and Allen's report noted that "both indicators of error were discounted at the time as being themselves flawed." During the fabrication process, technicians simply assumed the perfection of the mirror and of the reflective null corrector and rejected information from other independent tests, convincing themselves that no problems existed.

Discovery touches down at Edwards Air Force Base, Calif., on 29 April 1990. Photo Credit: NASA

The errors went back to 1981-82, when Perkin-Elmer and NASA were both distracted by cost and schedule difficulties. Allen's report particularly condemned Perkin-Elmer's quality control and communications failures, as well as NASA's own failure to correct them. In orbit, the spherical aberration was particularly obvious in its effect on Hubble's wide-field planetary camera and faint object camera, both of which suffered in terms of their spatial resolution and their ability to acquire images of distant sources. Having said this, the aberration was well characterised and stable and, over time, enabled astronomers to optimize the results obtained by Hubble with sophisticated techniques, such as "deconvolution," whereby software algorithms and image processing methods removed many of the blurring effects of optical distortion. Spectroscopy was less severely affected, because the instruments required less focused light and by increasing the exposure times it became possible to gather valuable images. However, the jittering of the solar arrays left Hubble's high-speed photometer virtually useless. Nevertheless, by the end of 1991, the telescope had made almost 2,000 quality observations of hundreds of astronomical objects, including storms on Saturn and images of Pluto's moon, Charon.

At the start of the following year, 1992, a quarter of all the papers presented before the American Astronomical Society drew on Hubble data. A repair mission, to be conducted no earlier than the fall of 1993, was critical in order to restore the telescope to its pre-flight billing and, although the primary mirror could not be replaced, a new device—the Corrective Optics Space Telescope Axial Replacement (COSTAR)—was built to restore its vision. COSTAR was manifested onto the first shuttle servicing mission to Hubble. Many senior administrators had little faith that the repair would work, but its success contributed greatly to a changing attitude toward the shuttle. As for Hubble itself, hardly anyone remembers the circumstances surrounding the spherical aberration today; far more detail abounds about its astounding scientific discoveries, its contributions to physics and astronomy and cosmology, and its importance to humanity as a species. The mirror problem is now little more than a footnote in history … and it should be, for Hubble has overcome the torment of its early childhood and performed grandly.

When the crew of the final shuttle servicing mission departed the telescope in May 2009, they left an observatory far more powerful and considerably more capable than even the magnificent showpiece which STS-31 had launched, almost two decades earlier. In the words of John Grunsfeld, who visited the telescope in space more times than any other human being, the honor and the privilege of being involved with such an icon made it worthy of the risk to his own life. Doubtless the other astronauts associated with Hubble feel the same way. "Hubble is worth risking my life," he once said. "It's that important. It's teaching us so much about our world, the Universe, who we are and our place in the cosmos."

And today, in 2015, after 25 wonderful and illuminating years, Hubble remains important and its teaching goes on.

 

Copyright © 2015 AmericaSpace - All Rights Reserved

 

---