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Happy 25th birthday, Hubble Space Telescope

It almost failed before it had even begun, yet it has far outlived its planned lifespan, becoming a treasure of untold value. Crave talks to some of the engineers who've kept it going.

The Butterfly Nebula, captured by the Hubble Space Telescope in 2009. NASA, ESA and the Hubble SM4 ERO Team

Twenty-five years ago today, the Hubble Space Telescope commenced its operations -- following a series of frustrating setbacks that didn't end even after it was locked into a low-Earth orbit.

Design on the telescope began in 1978, with a projected launch date sometime in 1983. This had to be pushed back to 1984 and then 1986 when the project ran over budget -- and when the construction of the Optical Telescope Array and the mirror inside it was mismanaged, causing the schedule to slip further and further behind.

Then 1986 rolled around. On January 28, 1986, the Challenger space shuttle orbiter launched on a mission, carrying seven crew. Just 73 seconds into its flight, the space shuttle broke apart, killing all seven crew members, destroyed by the failure of an O-ring socket that leaked pressurised burning gas, which in turn resulted in structural failure.

The Challenger had been scheduled to carry the Hubble Space Telescope into low-Earth orbit later in 1986.

Nevertheless, the tragedy had a thin silver lining for Hubble -- the team on the ground was able to finish preparing the launch software, as well as perform more thorough tests and checks on the telescope. It finally launched in 1990 aboard the space shuttle Discovery, commencing operations on April 24 of that year.

Since then, Hubble has made nearly 137,000 trips around Earth and captured data and images of more than 38,000 objects in space. Such data has led to the rewriting of astronomy textbooks and to NASA calling Hubble the "most significant advance in astronomy since Galileo's telescope" in the 1600s.

Yet Hubble's trials were not over with its launch. Remember the OTA mirror? It turned out that the primary mirror was ever-so-slightly the wrong shape -- off by such an infinitesimal amount, too flat around the edges by just 2.2 micrometres (a micrometre is a thousandth of a millimetre). It doesn't sounds like a lot, but the effect on the images that came back from Hubble was huge -- they were blurry.

The same image taken on the flawed Wide Field Camera 1 (left), and its replacement, the Wide Field Camera 2; or, the difference 1/50th the width of a human hair can make. NASA

The solution was the Corrective Optics Space Telescope Axial Replacement, designed by Ball Aerospace, one of the contractors signed on to make an instrument for the telescope in the 1970s.

COSTAR took around 28 months for Ball to develop -- where usually it would take around four years -- and was installed on the very first Hubble service mission in 1993. It was a series of small, coin-sized mirrors very carefully positioned in front of the misshapen mirror that corrected the curve. COSTAR came to be known as "Hubble's eyeglasses".

Since then, Ball has created every new instrument for upgrades on the Hubble telescope.

"Ball Aerospace has been involved with Hubble since the late 70's when we were selected to build one of the original science instruments," said Ball senior program manager John Troeltzsch, who worked on three of the instruments. "Since then, Ball Aerospace has built seven science instruments for the Hubble Space Telescope, two star trackers, five major leave-behind equipment subsystems and more than eight custom tools to support astronauts during servicing missions. The five science instruments now operating on the telescope were all designed and built by Ball.

"One of the most exciting moments of my career was sitting in the control room at NASA's Goddard Space Flight Center and watching an astronaut install the corrective optics, or COSTAR, into the Hubble Space Telescope, knowing I had touched the instrument on Earth just 10 days earlier and it would allow Hubble to return the magnificent science we now enjoy," Troeltzsch said.

Astronaut John Grunsfeld photographed by astronaut Andrew Feustel on a Hubble servicing mission in May 2009. NASA

It was originally projected that the Hubble telescope would have a life span of just 15 years. That it is expected to last at least twice that -- projections have it going for at least another 10 years -- is incredible, particularly after such a shaky start. This is partially because the Hubble was built to be upgradeable, with instrumentation that could be repaired and replaced.

This took place over five servicing missions: SM1, flown by Endeavour in 1993, which saw the installation of COSTAR; SM2, flown by Discovery in 1997; SM3, flown by Discovery and Columbia in 1999 and 2002 respectively; and SM4, flown by Atlantis in 2009. Each of these missions saw the installations of new instruments to keep Hubble up to date -- no mean feat, Ball director of advanced imaging Mark LaPole explained.

"The biggest and most obvious challenge is the work on Hubble is done while orbiting the Earth by space walking astronauts. All of our instruments and tools must be compatible with the bulky gloves on the spacesuits," LaPole said. "In addition, the space environment is very hot and very cold as the telescope and shuttle go around the Earth every 96 minutes they go from full sun to complete darkness. This is a very demanding environment to make upgrades and repairs."

SM4 saw a critical upgrade to the Hubble's instrumentation, with the installation of two new observation instruments: the Cosmic Origins Spectrograph for ultraviolet spectroscopy; and the Wide Field Camera 3, the telescope's most technologically advanced instrument for taking images in the visible spectrum. Those gorgeous, high-resolution space images Hubble has been taking in the last few years? Those are thanks to the WFC3.

Yet, like the launch of the Hubble, SM4 was plagued with problems -- and nearly didn't happen at all. This is because of the space shuttle Columbia, which disintegrated on re-entry in February 2003 -- once again killing all seven crew members.

After this, NASA decided that all space shuttles needed to be able to reach the International Space Station if in-flight problems arose -- a safe haven in times of difficulty. But the ISS is on a different orbital altitude from the Hubble, meaning that a shuttle would be unable to visit both in the same mission.

Plans for the final upgrade of the Hubble telescope were scuttled, until, amid public outcry and requests from Congress, NASA Administrator Sean O'Keefe agreed to review the mission. Initially, a mission was proposed in which a robot would complete the installation. But when a new Administrator, Michael Griffin, came on board in 2005, he agreed to a manned mission -- a Hail Mary for the Hubble telescope's last hurrah.

There are no future servicing missions planned -- yet, Troeltzsch said, the Hubble telescope will remain relevant for years to come. Even after its replacement, the James Webb Space Telescope, with a 6.5-metre mirror compared to the Hubble's 2.4-metre mirror, is launched, currently scheduled for 2018.

"Hubble combines a very human scale with its spacewalking repairs and upgrades with a cosmic scale that stretches across the universe. People relate to both scales at a very personal level," he said.

"Through servicing, Hubble has been able to stay current with technology and the frontiers of scientific exploration. This has kept it relevant. I think it will remain relevant as long as it is collecting distant star light to be used to answer scientific questions. Then it will become part of our collective history for future generations to marvel at."

Hubble's delightful derriere, photographed from the space shuttle Atlantis after the completion of a servicing mission in 2009. NASA

Eventually, the Hubble's instruments will start to fail. The gyroscopes, which help point the telescope at its targets, wear out pretty quickly. They could be the first part to fail. For a time, the Hubble will continue limping along, sending back data; then, eventually, the cost of operation will exceed the telescope's scientific value, and it will be retired.

But that doesn't mean its life is over, not quite yet.

"I believe the Hubble still has plenty of life and we hope it has a graceful ending; scientific papers will be written for decades after it is retired. Having overlap with the James Webb telescope will allow scientists to fuse the data from the two and produce discoveries we can't imagine today," LaPole said.

"It's not too late for another servicing mission to the Hubble," he added, "perhaps not as broad as what we could do with the Space Shuttle, but there are creative ideas in our dreams and on our whiteboards."

When it is finally retired, eventually its orbit, which is very low to begin with, will start to sink lower, caused by atmospheric drag. In times of solar maximum -- the sun's peak activity period, occurring on an 11-year cycle -- the atmosphere expands, which will speed up this process. (The next solar maximum is due in around 2024.) It will sink so low that it will fall to Earth; most of the telescope will be burned up in re-entry, with only a few fragments falling as far as the surface.

This image of the Tarantula Nebula, released for Hubble's 22nd birthday in 2012, is Ball Aerospace senior program manager John Troeltzsch's favourite Hubble image because it shows how far the telescope has come. ESA/NASA

Yet its legacy will last a long time into the future.

"Hubble has helped humanity make huge advances to the questions: Who are we? Where did we come from? What else is out there? These are fundamental questions that people have pondered for all of history," Troeltzsch said.

"With Hubble we have seen stars forming and dying. We have seen comets collide with another planet in our solar system. We have seen the universe when it was forming. We have seen planets forming and orbiting other stars. It has given us so much, and its data and discoveries will be used by scientists for hundreds of years to come."