It's getting harder to find good help these days. So these space engineers built their own
- By Michael Behar
- Air & Space magazine, July 2005
(Page 4 of 5)
After a pre-programmed computer sequence initiates the docking procedure, short bursts of pressurized air begin to slowly propel the coupler toward the satellite. A barbed hook on the end of the coupler is supposed to snag the inner lip of the satellite’s thruster cone. The two craft barely touch when the satellite suddenly swings sideways. A second try produces a similar result. Only on the third attempt—with Bailak and Allen physically nudging each craft to maintain the proper alignment—does the docking succeed. Later, I try the same procedure on a simulator. After a promising start, I crash the docking craft into the virtual satellite, tearing off half its solar panels and sending it into a death spiral.
Bailak and Allen brush off my cosmic train wreck as a minor hiccup along the robotic servicing learning curve. Besides, they say, autonomous rendezvous and docking are precisely the problems that projects like DART and XSS-11 are meant to address. DART’s program manager, Jim Snoddy, calls his mission “a prototype of many things to come,” including the orbital assembly of spacecraft bound for the moon and Mars. “When we start putting more pieces in space, we’re going to have to start putting them together,” he says.
A major hurdle will be developing a robotic arm that can adjust its sensitivity as it pushes and pulls on connectors and cables. Ideally, a robot would react to physical resistance much as a person does—by turning a screw more slowly and carefully, for instance, if it felt the threads beginning to strip.
Gerd Hirzinger, director of the Institute of Robotics and Mechatronics, part of the German space agency, DLR, hopes to overcome this problem with a remotely operated mechanical arm called ROKVISS (Robotic Component Verification on ISS). ROKVISS is a double-jointed arm about two feet long, with a self-contained power supply and a finger-length stylus tool. A Russian resupply craft delivered ROKVISS to the space station in December. It was mounted to the outer wall of the Russian Zvezda module, where it could be operated from a ground station located about 15 miles from Hirzinger’s lab outside Munich.
In March, ROKVISS completed its first set of maneuvers, “proving that the concept of torque-controlled joints” is mature enough to work in space, says Hirzinger. The joints, he adds, are “similar to human muscles—you can them make stiff or soft.” The ROKVISS arm also incorporates a stereo camera. According to Hirzinger, once the robot makes contact with a contoured shape, the arm can either maintain an even pressure anywhere along the object, or apply “high-fidelity force feedback” to vary the pressure. Imagine hand-sanding an intricately carved wooden table leg: If you don’t adjust your pressure to accommodate the leg’s curves, the finish will become uneven, smoother where it’s convex but still rough along the concave surfaces. Hirzinger plans to continue testing ROKVISS aboard the station for a year. “If the joints turn out to work perfectly in space,” he says, “then we’ll immediately start building a seven-degrees-of-freedom free-flying robot.”
Eventually, the follow-on system would be used to demonstrate in-orbit satellite servicing.
Meanwhile, in Houston, Rob Ambrose’s group has built a mobile platform for Robonaut. Funded by NASA and the Pentagon’s Defense Advanced Research Projects Agency, Robonaut has simmered along since 1996 as a low-priority technology development effort. Despite its popularity with the press and its Hollywood good looks, the humanoid robot has never been called for an assignment in space.
Ambrose hopes NASA’s recent focus on building a lunar base could change things. Recently his team removed the robot’s single zero-G leg and mounted its torso to a mobile platform based on the Segway scooter. They wired Robonaut’s computer interface directly into the Segway’s control system, giving the robot control over its balance and motion. “We would like to put our robots in a precursor role: setting up a work site or habitat on the moon,” says Ambrose, who is now looking for a four- or six-wheel platform suitable for rough lunar terrain. “If I were going to be sent to the moon, I would want my habitat already making oxygen, already 72 degrees, holding air, and not leaking.”
Back at the University of Maryland, Ranger’s successors continue making dives in the neutral buoyancy tank, but now Akin is adapting them for more generic work. His team is also working with NASA’s Astrobiology Science and Technology Experiment Program to develop a Ranger-type robot that could collect planetary samples—perhaps on Jupitor’s moon Europa.