Rescuing the Hubble space telescope

November 15, 2013 by Jennifer Chu
Space Shuttle Endeavour astronauts discussed their 1993 mission to repair the ailing Hubble Space Telescope. From left: mission specialist Tom Akers, pilot Ken Bowersox, mission commander Dick Covey, mission specialist and AeroAstro professor Jeff Hoffman, and payload commander Story Musgrave. Credit: William Litant

In the past two decades, the Hubble Space Telescope has produced thousands of staggering images of the universe—capturing colliding galaxies, collapsing stars, and pillars of cosmic gas and dust with its high-precision cameras. These images have driven many scientific discoveries, and have made their way into popular culture, having been featured on album covers, fashion runways, and as backdrops for sci-fi television episodes.

With Hubble's advanced capabilities today, it's hard to recall that the was once gravely threatened. But shortly after its launch in 1990, scientists discovered a flaw that jeopardized Hubble's entire endeavor. What followed was a political and public backlash against the $1 billion mission—and NASA, the agency that oversaw it.

For the next three years, engineers scrambled to design a mission to repair the telescope in space—an ambitious plan that would result in the most complex Space Shuttle mission ever flown.

"[Hubble] was never meant to be a suspense story," Jeffrey Hoffman, a member of the original astronaut crew charged with repairing the telescope, said this week at MIT. Nevertheless, at the time, the future of Hubble—and of NASA itself—seemed to hinge on the repair mission.

On Dec. 2, 1993, Hoffman and six other astronauts aboard Space Shuttle Endeavour began an 11-day mission, named STS-61, that involved five spacewalks—the most of any shuttle mission—to restore Hubble's vision.

This week, Hoffman, now a professor of the practice in MIT's Department of Aeronautics and Astronautics, was joined by other members of the STS-61 crew in reflecting on Hubble's rescue mission in an all-day symposium held in MIT's Bartos Theatre. Talks and panel discussions—often with the air of a warm reunion—explored Hubble's initial promise; its failure shortly after launch; and the planning, training, and execution of a rescue mission to fix the telescope.

Hubble's backlash

The first inkling of a problem came during a NASA press conference held to present the first image taken by Hubble from space: The image, of a far-off star, appeared fuzzy. Scientists soon discovered a "spherical aberration": Due to a defect in the manufacturing process, the telescope's primary mirror had been ground too flat, setting its curvature off by less than the width of a hair.

"The unthinkable had become fact," said James Crocker, then an optical engineer at NASA.

Once word of the defect spread, Hoffman recalled that NASA and the astronomy community experienced "a maelstrom of public opprobrium," mainly circling around the same question: "How did you screw up so badly?"

To illustrate the public feeling at the time, John Logsdon, former director of the Space Policy Center at George Washington University, presented editorial cartoons deriding the mission with pictures of lemons in space and images of static, "courtesy of the Amazing Hubble Telescope." Overall, Logsdon observed, public perception of the problem focused less on the defects in space than on the agency on the ground.

"NASA was very much at risk," Logsdon said.

Preparing a fix

Following the discovery of Hubble's defective mirror, engineers at NASA faced immense pressure to fix the problem. Crocker eventually experienced what he called a "eureka moment" in the most unlikely of places: a shower in Munich, where he had traveled to appeal to the European Space Agency for possible solutions. On a break in his hotel room, he was adjusting the showerhead—a European design that extends or retracts to accommodate one's height—when an idea came to him: Why not outfit Hubble with corrected mirrors built on robotic arms that can extend into the telescope and retract into place, just like an adjustable showerhead?

NASA engineers ran with the idea, building the Wide Field and Planetary Camera 2, or WFPC2, to replace Hubble's defective mirror. Getting the piano-sized instrument into the satellite required 11 months of training by Hoffman and six other astronauts, who spent more than 230 hours in a water tank, choreographing intricate maneuvers and learning to use more than 150 tools. Meanwhile, engineers tested and retested the instruments to be installed on the telescope.

Frank Cepollina, then NASA's manager of space servicing capabilities, remembers that at the time there was "great turmoil in checking every socket and bolt."

A spacewalk to save NASA

All preparations led up to Dec. 2, 1993, when the STS-61 crew launched. On the mission's third day, the crew used the shuttle's robotic arm to grab hold of the free-floating telescope, attaching it to the shuttle's cargo bay, an event that prompted mission commander Dick Covey to announce: "We've got a firm handshake with Mr. Hubble's telescope."

The next day, Hoffman and payload commander Story Musgrave embarked on the mission's first spacewalk, during which Hoffman, anchored to the robotic arm, replaced two gyroscopes on the telescope.

Astronauts Kathryn Thornton and Thomas Akers set out on the second spacewalk to replace one of the telescope's solar panels, which had begun to list. After the astronauts disengaged the panel from the telescope, Hoffman remembers watching the array drift off into space, "like some prehistoric bird floating away—we were mesmerized."

Hoffman and Musgrave performed the mission's third spacewalk to swap out Hubble's defective mirror with the 620-pound WFPC2—the crux of the mission, and one that saw Hoffman anchored to the robotic arm, with Musgrave free-floating inside the telescope as Hoffman fed tools to him.

"It was a little like working under a car," recalled Hoffman, who said the procedure was so complex that the shuttle crew had to talk them through each step. The procedure was a success, as NASA's ground controllers found that the new mirror passed all its initial tests.

The remainder of the mission went largely according to plan, except for one hair-raising moment on the final spacewalk. On his previous outing, Hoffman had noticed that Hubble's magnetometers, located at the very tip of the telescope, were flaking. To prevent more debris from possibly damaging equipment, pilot Kenneth Bowersox and mission specialist Claude Nicollier fabricated makeshift covers out of insulation to wrap around new magnetometers.

During the fifth and final spacewalk, Hoffman and Musgrave replaced the telescope's magnetometers with the insulated upgrades, a maneuver that required removing screws and placing them in a bag while removing one instrument. In the process, a screw got away, floating free of the astronauts' grasp. While seemingly harmless, the 3-millimeter screw had the potential to dent the telescope or the shuttle.

Hoffman, anchored to the shuttle's arm, reached in vain for the screw, while Nicollier tried moving the arm farther out. But both the arm and the screw were moving at the same speed. In a spur-of-the-moment action, Bowersox reprogrammed the shuttle's computer to reset the arm's maximum speed, allowing Hoffman to reach the screw. From then on, the astronauts would refer to the escapade as "the Great Screw Chase."

Continuing success

Since that first repair mission, astronomers have used Hubble to collect thousands of stunning images of the universe and make countless discoveries, with more than 11,000 published papers based on Hubble images. The telescope has undergone four more servicing missions to replace old instruments and add new capabilities.

Of Hubble's future, Cepollina said: "As long as the telescope can collect photons, and we can provide next-generation instruments, we should keep truckin'."

For the astronauts who rescued Hubble, disengagement from the telescope was bittersweet.

"It was a little sad to let the telescope go," Bowersox recalled. "It was like saying goodbye to a friend. It was a great, magical time."

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not rated yet Nov 15, 2013
One threat to Hubble is that it is seen as a competitor of funding to the James webb space telescope. It ould be relatively cheap to send astronauts up to fiix the gyros -for instance with a double* Soyuz mission launched from Kourou- but as long as James Webb is not launched it will not happen.
*One orbital craft, one module with extra fuel and spare parts.
1 / 5 (11) Nov 15, 2013
.......I see your point Birger, but it seems the James Webb is more complementary to Hubble than a direct competitor.

The dominant purpose of JW uses spectroscopy to detect objects in the infrared range whereas Hubble is useful only in the visible light spectrum. That doesn't necessarily preclude JW from being tweeked for spectroscopy in the visible spectrum, but it won't function nearly as efficiently in that region of interest as Hubble presently does. However newer earth based technology is providing results comparable to Hubble, so no matter how you look at (or through) it, Hubble seems doomed.

2.3 / 5 (3) Nov 15, 2013
Nice story. Real Sci-"fi".
3.5 / 5 (8) Nov 15, 2013
Everybody knows that space is a liberal lie. We are floating in the center of a sphere of ether! I've made a website with lots of complicated words to prove my point.
1 / 5 (2) Nov 15, 2013
The error with the Hubble Mirror is yet another example of the failure of American Capitalism.

American corporation Perkin-Elmer was commissioned to build the optical components of the Hubble Space Telescope. The construction of the main mirror was begun in 1979 and completed in 1981. The polishing process ran over budget and behind schedule, producing significant friction with NASA. Due to a miscalibrated null corrector, the primary mirror was also found to have a significant spherical aberration after reaching orbit on STS-31. A NASA investigation heavily criticized Perkin-Elmer for management failings, disregarding written quality guidelines, and ignoring test data that showed this miscalibration.
1 / 5 (11) Nov 15, 2013
There is not enough money left in the NASA budget to fix Hubble, because it's being spent on the Agency's first priority, set by Obama himself, to improve the self-esteem of Muslims worldwide.
2.2 / 5 (13) Nov 15, 2013
The James Web Telescope will be a very important addition to the space sciences. Buying time on Hubble is a competitive activity, and that makes any additional instrument for the purpose of exploration and discovery a valuable asset. JWT will certainly not displace Hubble. Keep on truckin'!
5 / 5 (3) Nov 15, 2013
The error with the Hubble Mirror is yet another example of the failure of American Capitalism..

And I suppose that you know of an economic system that never makes mistakes?
1 / 5 (2) Nov 16, 2013
I grant some level of error in any system. However, the U.S. Capitalist system is nothing but failure after failure after failure.

1.4 / 5 (10) Nov 16, 2013
Considering that I actually designed and built the Hubble telescope, and then launched it into orbit and went up on all the maintenance missions as well....

And the Merikens have been paying loans and interest on money that never existed, since the private bank called the Federal Reserve loaned it to them......

I'd say I have done pretty fucking good out of all this.

Now as the Hubble is leaving the cosmos... and heading into galactic space all I can say is "Thanks for all the fish."

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