Frank Cepollina takes repair calls to new heights.
- By Robert Zimmerman
- Air & Space magazine, May 2010
(Page 4 of 5)
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.
Cepollina concedes that at the time of the academy study, certain critical steps in robot servicing had not been demonstrated in space. But many of them have been since. The Defense Department/NASA Orbital Express mission, flown in 2007, showed that one satellite could dock with another automatically, use a robot arm to change the second satellite’s modular components, and transfer fuel. A low-cost Air Force satellite called XSS-11 was able to maneuver precisely around other spacecraft, and Dextre was installed on the space station in 2008.
“Orbital Express did all the things the academy said would be too difficult and risky,” says Cepollina. As a result of these projects, space robotics has convinced some former skeptics. “The technology has not advanced that much [since the academy study],” says Akin. “But the perception of it has changed tremendously.”