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Two-armed Dextre robot, which will be used to demonstrate orbital refueling. (NASA/Human Spaceflight)

Mr. Fix-It

Frank Cepollina takes repair calls to new heights.

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(Continued from page 2)

Cepollina knew that if he could marshal public and Congressional opinion without causing harm to his superiors, they would eventually go along. Sure enough, NASA headquarters finally approved the repair mission, with Cepollina in charge.

He remembers it as the most terrifying time in his career. The future of in-space servicing, an idea he had promoted for years, hinged on this one flight. And immediately after space shuttle Challenger rendezvoused with Solar Max on April 8, 1984, the plan started to unravel. Astronaut George “Pinky” Nelson donned a Manned Maneuvering Unit backpack and flew from the shuttle to the satellite, but was unable to capture Solar Max with a specially designed piece of equipment (it turned out later that a grommet on the satellite—which didn’t appear in blueprints—blocked the docking mechanism).

After three attempts, Nelson succeeded only in setting the spacecraft tumbling. It took a series of hastily prepared software uploads by the ground, combined with a bit of luck when the nearly dead spacecraft drifted into sunlight just long enough—10 minutes—to charge its batteries, to stabilize the spacecraft so that the Challenger astronauts could grab it with the shuttle’s robot arm and haul it into the cargo bay. Finally back on script, Nelson and crewmate James “Ox” Van Hoften breezed through the repair. “They had to do two days’ worth of stuff in one day, and they finished it all,” remembers Barbara Scott, who was the payload operations engineer for the repair mission and is now the Hubble Flight Software manager at Goddard. As a result, Solar Max operated for another five years, recording more than 12,500 solar flares. Just as significantly, the failed attitude control module was returned to the ground, refurbished, and installed on another spacecraft, the Upper Atmosphere Research Satellite. That spacecraft was launched in 1991, and operated in orbit for 14 years. “Second-hand Rose,” Cepollina quips.

The Solar Max repair gave NASA confidence in its plan to send astronauts to Hubble periodically to replace cameras and other scientific instruments with more capable ones, just like an observatory on the ground. For the first Hubble service mission—which also corrected the telescope’s out-of-focus mirror—the Goddard team came up with procedures for replacing three failed gyroscopes, two electronic control units, and eight fuses.

Later missions have replaced Hubble’s instruments and gyroscopes several times over, installed a more powerful set of solar panels to replace the ones brought up in 1993, replaced the telescope’s computer and batteries, and repaired damaged insulation. After five upgrades, Hubble no longer carries any of the scientific instruments it had at its 1990 launch.

Despite the unqualified successes, the final servicing mission almost didn’t happen. After space shuttle Columbia and its crew were lost in 2003, NASA cancelled all flights to destinations other than the International Space Station, for fear that if the vehicle were damaged, the crew would be unable to return to Earth. With astronauts barred from visiting Hubble, Cepollina pushed for a daring alternative: He would send a robot to repair the telescope, using procedures and tools honed by more than a decade of planning astronaut repair missions.

In the interest of time, the Goddard team chose an existing robot for the job: the Canadian Special Purpose Dexterous Manipulator, which was already built and waiting to be launched to the space station (where it’s now known as Dextre). Starting in 2004, Cepollina’s team worked feverishly in Maryland and in Canada to prove that Dextre, using tools attached to the end of its robot arm, could accomplish tasks normally done by astronauts: replacing two large science instruments, a fine-guidance sensor, gyroscopes, and batteries. The work involved lots of unbolting and bolting, as well as numerous electrical and data connections. In practice sessions using high-fidelity Hubble mockups, Dextre showed that it could handle the work. The team even simulated the two-second time delay that skeptics thought would be a severe handicap when the robot was tele-operated from the ground. Not a problem.

Once again Cepollina worked the PR channels, appealing directly to Congress and the media, pushing a robotic mission. This time, though, the answer was no. NASA asked the National Academy of Sciences to review its plans for Hubble servicing, and the verdict, rendered in December 2004, was that a robot-only mission would push technology too far, too fast. It wasn’t impossible, said the academy, but there were too many unknowns—including whether an automated spacecraft could rendezvous and dock safely with Hubble—to pull off a complex robot mission with just three years of planning. NASA went with astronauts instead.

“I do think they [the academy] were unduly conservative,” says David Akin, a space roboticist at the University of Maryland who helped Cepollina’s team with underwater testing of their procedures. But Cepollina accepted the finding and turned immediately to planning the astronaut repair, while keeping the robot option on the back burner. The tools and procedures developed for the robot mission made the astronaut service call far more efficient, he says. “It allowed [the astronaut crews] to do seven or eight days of work in five.” And during the last servicing flight his team was able to conduct experiments, in parallel with the astronaut repairs, to evaluate capabilities such as robot vision. “We never stopped moving [to develop robotic servicing].”

Now, he says, “I’m proposing to take the next step.” Congress has given him $70 million—a large amount in the field of space robotics—for a space station experiment to demonstrate robotic satellite refueling. Ground tests are under way at Goddard, and by the end of this year Cepollina plans to use Dextre to demonstrate all the steps of refueling on a hardware mockup equipped with standard satellite ground refueling valves, connections, and insulation blankets. The test goes by the name R2D2, for Robotic Re-Fueling Dexterous Demonstration.

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