What do the "Fast and Furious" movies and the Hubble Space Telescope have in common?
They both require the willing suspension of disbelief.
That's to be expected for a movie like "Furious 7," with cars and drivers falling from airplanes and flying through buildings. But the Hubble Space Telescope? The most powerful -- and expensive -- observatory ever built?
Yes, suspension of disbelief has been called for time and again throughout Hubble's history, starting with its launch 25 years ago April 24, the discovery of its famously flawed mirror, the MacGyver-like repairs by spacewalking astronauts and its subsequent rise from the ashes of disaster to the pinnacle of scientific success.
And like a cat with nine lives, Hubble survived another near-death experience when a final servicing mission, needed to replace failing gyroscopes and other components, was canceled in the wake of the 2003 Columbia space shuttle disaster amid concerns about astronaut safety.
But finally, after the development of shuttle heat shield repair techniques, the servicing flight was reinstated and Hubble was overhauled one last time in May 2009. Two new instruments were installed, two others were repaired, its gyros and batteries were replaced, a new data computer was plugged in and a fine guidance sensor was swapped out.
Since then, one stabilizing gyro has failed but only three are needed for normal operations, and software has been developed to continue science operations with just one if necessary. Its instruments and other subsystems are generally healthy and engineers are optimistic Hubble will remain scientifically relevant at least through 2020 if not longer.
Celebrating the 25th anniversary of Hubble's launch -- and looking ahead to the 30th -- even astronomers who work with the observatory on a daily basis still find the saga hard to believe.
"That's part of the Hubble story," said Jason S. Kalirai, an astronomer at the Space Telescope Science Institute at Johns Hopkins University in Baltimore.
"It was a huge program, then it was a disaster, and then astronauts, these heroes, risked their lives to go fix it and then it's a huge success. You couldn't script something better than that, right? You couldn't make a movie that was better than that. It's been great."
NASA hopes to launch Hubble's successor, the much larger infrared-optimized James Webb Space Telescope (JWST), in late 2018. Astronomers are looking forward to using both telescopes in tandem, for as long as Hubble is able, to study the universe across a wide range of wavelengths, from near ultraviolet through visible and the infrared, to gain deep insights into the life cycles of stars and the evolution of the universe.
But JWST, one of the most complex spacecraft ever designed, is not yet in orbit and no one knows what challenges it may encounter or how successful it might ultimately prove to be. In the near term, Hubble remains the world's preeminent space observatory.
Looking back on a quarter century of trail-blazing observations, most astronomers would agree the Hubble Space Telescope is the most scientifically productive spacecraft ever launched, an unrivaled discovery machine that has become an icon of big science and American ingenuity.
In the process, the space telescope has answered many of astronomers' most pressing questions and shed light on previously unknown phenomena that, in turn, raise still more questions about the birth, evolution and eventual fate of the cosmos.
Taking advantage of Hubble's perch high above Earth's obscuring atmosphere, the space telescope has pinned down the age of the universe -- 13.8 billion years -- and helped confirm the existence of dark energy, the mysterious force speeding up the expansion of the cosmos.
Hubble also has confirmed the existence of supermassive black holes lurking in the hearts of most, if not all, mature galaxies, provided glimpses of galaxies forming within a few hundred million years of the big bang and helped map out the life cycles of stars, from infancy to the extremes of old age, from slowly-cooling senescence to mind-bending supernovas.
Along the way, Hubble has provided flyby-class views of planets in Earth's solar system, giving astronomers a ringside seat for unexpected events like comet Shoemaker-Levy 9's spectacular 1994 crash into Jupiter, dust storms on Mars and flickering auroras at the poles of Jupiter and Saturn.
It also discovered four of Pluto's five moons and was even able to detect small, dim bodies in the remote Kuiper Belt, candidates for closer examination in the years ahead by NASA's Pluto-bound New Horizon's spacecraft.
And in an achievement no one could have expected when Hubble was launched, the telescope has even managed to snap a picture of a planet orbiting another star and spectroscopically detected major constituents of an exoplanet's atmosphere.
Twenty-five years after Hubble's launch, the Space Telescope Science Institute still receives six to seven times the number of observing proposals than can be accommodated.
Among its current projects is a search for infant galaxies even closer to the big bang, using the gravity of intervening galactic clusters to magnify the feeble light of background, much more remote objects; and work to perfect a new technique to greatly extend astronomers' ability to directly measure interstellar distances, expected to improve understanding of the effects of dark energy
"There is no question Hubble is in many ways unique," said Mario Livio, an astrophysicist at the Space Telescope Science Institute. "First of all, its longevity is really amazing. It's not just that it has been there 25 years, but because of five (shuttle) servicing missions, it has been continuously renewed and repaired. And so, at some level, the telescope is now in almost its best shape in terms of instrumentation and so on.
"In terms of scientific achievements, the fact that Hubble is this sort of all-purpose telescope, there is essentially no area of astronomy and astrophysics where Hubble didn't contribute something quite significant. There are sometimes very specific missions that do great things in one particular field, (but) Hubble has done great things in everything that is related to modern astronomy."
And then, he said, "there is the drama."
Repairing Hubble's flawed optics and upgrading its instruments and subsystems over two decades turned "what could have been one of the greatest failures of big science to possibly its greatest success," Livio said. "So that story, 'the telescope that could,' if you like, is in itself a huge story."
As for its longevity, John Grunsfeld, a spacewalking member of the final three shuttle servicing missions and now NASA's director of space science, points out an entire "generation of kids who have grown up with Hubble."
"For some of these kids, Hubble has always been in their lives, has always been in their textbooks," he said. "There are now professional astronomers who have grown up with Hubble always being there."
Including former astronaut Kathryn Thornton's daughter. The elder Thornton, now a professor of engineering at the University of Virginia, was a shuttle spacewalker on the mission that repaired Hubble's flawed optics.
"When I launched on that servicing mission my oldest daughter was 11," she said. "And then some years later, she got her Ph.D. in astrophysics using Hubble data. Not only that, her thesis advisor used Hubble data. So I'm like a Hubble grandmother! It absolutely is amazing."
A TORTURED HISTORY
The idea for a space telescope dates back to the 1920s when a German scientist first wrote about the advantages of placing a telescope above Earth's atmosphere. The American astrophysicist Lyman Spitzer proposed a space telescope in a 1946 paper titled "Astronomical Advantages of an Extra-Terrestrial Observatory."
In 1969, the National Academy of Sciences recommended building a space telescope with a 120-inch mirror. NASA backed the project in 1971 but Congress balked at the expected price tag, estimated to be in the neighborhood of $500 million. After additional lobbying by NASA and well-known astronomers, a decision to reduce the size of the primary mirror to 94.5 inches, and the participation of the European Space Agency, Congress approved the Large Space Telescope project in 1977.
The Lockheed Missiles and Space Co. won the contract to build the spacecraft while Perkin-Elmer Corp., which had experience building optical systems for spy satellites, was tapped to fabricate the telescope's primary mirror.
The mirror was completed in 1981, two years before a planned launch in 1983. But NASA and its contractors ran into problems finishing the telescope and the launch schedule slipped to October 1986.
But it was not to be.
On Jan. 28, 1986, the shuttle Challenger was destroyed in a launch mishap and NASA's fleet of orbiters was grounded for a lengthy investigation and corrective actions to improve flight safety. Shuttle flights did not resume until 1988 and it would be another two years before Hubble, now valued at some $1.5 billion, would make its way back onto NASA's launch manifest.
Finally, to enormous fanfare and stratospheric expectations, Hubble was launched aboard the shuttle Discovery on April 24, 1990. Among the crew: pilot Charlie Bolden, now NASA administrator, and Kathryn Sullivan, the current head of the National Oceanic and Atmospheric Administration.
As pilot, Bolden was responsible for overseeing Hubble's deployment. Sullivan and veteran spacewalker Bruce McCandless were standing by to carry out an emergency spacewalk if anything went wrong. Astronaut Steven Hawley was operating the shuttle's robot arm for deployment. The commander was Loren Shriver.
In what became the next chapter in the Hubble space drama, one of the telescope's two rolled-up solar panels refused to unwind as expected after Hawley, operating the robot arm, pulled the observatory out of the cargo bay.
In the meantime, the space shuttle was in free drift, "which meant no jets could be firing," Bolden recalled. "So the vehicle was just kind of drifting around in space in all kinds of attitudes and the power guys began to really get worried about the batteries going dead on the telescope.
"I took Bruce and Kathy down (to the lower deck), got them dressed (for a contingency spacewalk), put them in the airlock and we started to depressurize. The airlock was completely depressed, and I think we were five minutes away from opening the outer hatch."
But in the nick of time, engineers on the ground finally figured out a solution. Commands were sent to the telescope, relaxing limits on a tensioning device in the array's reel mechanism and the panel deployed normally.
"Of the five people aboard that day, the two who had worked more than five years for this moment were the two who didn't see it," Sullivan laughed. "So Bruce and I only saw Hubble deploy on video like all the rest of you guys."
Discovery returned to Earth four days later, leaving a presumably healthy Hubble behind in orbit. About a month later, engineers took their first photo, a "first-light" image showing a nondescript star cluster known as NGC 3532. The picture was sharper than a ground-based image, and astronomers said they were pleased with the initial results.
"I'm tickled pink with what we've seen today," said James Westphal, the man in charge of Hubble's Wide Field/Planetary Camera. "We were expecting to see something that looked pretty much like a ground-based picture. So the fact that we're seeing something that is really obviously sharper really pleases us a whole bunch."
But not for long.
Subsequent efforts to precisely focus Hubble's optical system by commanding slight movements of the telescope's secondary mirror did not significantly sharpen the image. After an exhaustive series of tests, engineers discovered Hubble's presumably near-flawless 94.5-inch mirror had been ground to the wrong shape, a fundamental, hard-to-believe defect that somehow went unnoticed on the ground before launch.
Almost overnight, Hubble went from the most heralded telescope ever built to the butt of jokes on late-night television. It was one of NASA's darkest hours, with critics citing the Hubble failure as evidence NASA might not have the "right stuff" needed to build the International Space Station.
There was no way to fix Hubble's mirror in orbit. But applying Apollo 13-class ingenuity, engineers realized that the mirror's precisely fabricated defect offered a possible solution. Because it had been perfectly ground to the wrong prescription, opticians realized the problem could be corrected by installing small mirrors, ground to the opposite prescription, in the observatory's instruments.
NASA already was building a spare Wide Field/Planetary camera and precisely figured nickel-sized mirrors were inserted in the guts of the instrument to bring starlight to a crisp focus. To correct the beams going into Hubble's other instruments, NASA managers opted to replace one instrument, a high-speed photometer, with a complex device known as COSTAR that was equipped with multiple corrective mirrors on motorized arms.
Finally, in December 1993, the shuttle Endeavour blasted off, rendezvoused with Hubble and the telescope was pulled it into the ship's payload bay for servicing. Thornton and three other spacewalkers installed COSTAR and the Wide Field and Planetary Camera 2, along with a new set of solar arrays and gyroscopes.
Within weeks, spectacular images were downlinked proving Hubble's vision had been restored to razor-sharp clarity. And in a cosmic coincidence, Comet Shoemaker-Levy 9 smashed into Jupiter the following July, resulting in spectacular, widely-publicized images that left no doubt about Hubble's health.
In the weeks and months ahead, the once-ridiculed telescope became one of the most scientifically productive observatories ever built, chalking up a steady string of major discoveries and sending down a seemingly endless stream of stunning images.
"It's images have become part of our culture in our textbooks, magazines, art and even popular movies and TV programs," Ed Weiler, former Hubble project scientist, said before the final shuttle visit in 2009. "Although we probably never will be able to visit these places or objects, Hubble actually allows our human minds and spirits to travel light years and even billions of light years to the farthest reaches of the cosmos."
THE SECRET OF HUBBLE'S SUCCESS: SHUTTLE SERVICING MISSIONS
The secret to Hubble's success was NASA's ability to launch shuttle servicing missions to replace outdated or malfunctioning components, to repair systems that could not be replaced and to install new, state-of-the-art instruments to keep the observatory at the forefront of astronomy.
Four years after Hubble was equipped with corrective optics, astronauts on a second servicing mission installed two new instruments -- the Space Telescope Imaging Spectrograph and the Near Infrared Camera and Multi-Object Spectrometer, or NICMOS -- replaced a fine guidance sensor, a gyroscope and installed a solid-state data recorder.
After multiple gyroscope failures in the late 1990s, NASA managers decided to split a third servicing mission into two shuttle flights.
During Servicing Mission 3A, launched in December 1999, spacewalking astronauts installed a new flight computer, a second solid-state data recorder, another fine guidance sensor and a full set of six gyroscopes. During Servicing Mission 3B, launched in March 2002, another shuttle crew installed two new solar arrays, the Advanced Camera for Surveys, an experimental cooling system for NICMOS and a replacement power control unit.
A final shuttle visit was planned for 2005 or thereabouts. But on Feb. 1, 2003, the shuttle Columbia disintegrated during re-entry and the following January, then NASA Administrator Sean O'Keefe, citing concerns about crew safety, cancelled Servicing Mission 4. Because Hubble and the International Space Station are in different orbits, a Hubble repair crew could not reach safe haven aboard the lab complex if their shuttle suffered a Columbia-class problem.
But NASA eventually came up with heat-shield repair techniques and O'Keefe's successor, Michael Griffin, reinstated the fifth servicing mission after working out plans to process a second shuttle for an emergency rescue flight if necessary.
During the final visit in 2009, four spacewalkers working in two-man teams installed six new gyroscopes, a full set of six nickel-hydrogen battery packs, a new data computer and two new instruments, the $126 million Wide Field Camera 3 and the $81 million Cosmic Origins Spectrograph.
An upgraded fine guidance sensor was installed along with new insulation blankets and a grapple fixture that will permit attachment of a rocket motor at some point down the road to enable a controlled re-entry when Hubble's orbit decays to the point of no return.
Grunsfeld and his crewmates also repaired two science instruments, the Space Telescope Imaging Spectrograph, which suffered a power supply failure in 2004, and the Advanced Camera for Surveys, which malfunctioned in 2007. Neither instrument was designed to be repaired in space.
"What we did on that last mission was really hard, and there were a lot of folks who said we'd bitten off too much, that what we were trying to do with the repair of the instruments, the tiny screws, the pulling out circuit cards, that we wouldn't be successful and we'd end up with a degraded Hubble or we would have risked human lives for naught," Grunsfeld said. "And we achieved it, we achieved everything on that mission and a little bit more.
"And I think it's that spirit, where there's some high-performance challenge for a really good cause that allows people to work to a much higher level than they ever could. And if we could harness that kind of energy that's been put into Hubble for energy research on Earth, the problems of society that technology can address, if we had that kind of intensity ... I think we could do almost anything."
Grunsfeld was the last human being to touch the Hubble Space Telescope. Making his way back to the shuttle airlock after the crew's final spacewalk, Grunsfeld, who holds a Ph.D. in astronomy, said his final farewell.
"I was very uncertain going into the mission how I would personally feel, emotionally, going back into the airlock and knowing I would never see Hubble again," he said. "I was anticipating I'd be sad.
"But in the end, I actually felt thrilled, because we'd achieved everything and left Hubble in the best shape possible. I really felt like sending some friend off on something you knew was going to be positive. And we were all that way. It was a celebration."
With any luck, the celebration -- and discoveries -- will continue for years to come.