Shuttle Mission to Include More Tests of Robot Arm

SPACE shuttle Columbia, which was scheduled to blast off yesterday on NASA's 51st shuttle mission, will test a revolutionary control system for the Canadian-built robotic arm.

Astronauts will use the shuttle's 50-foot mechanical arm to manipulate an aluminum panel in the cargo bay. On-board television cameras will record movements of the arm and a computer will create an image that can be watched on a control monitor in the shuttle.

The activity will simulate tasks necessary for building the space station - a primary goal for the shuttle program.

In May, when Pierre Thuot, Rick Hieb, and Tom Akers stepped from the air lock of the shuttle Endeavor to rescue Intelsat 6, they made aviation history. It marked the first time a team of three astronauts had ventured into the near-vacuum of space. The crew could not have retrieved Intelsat 6 without the dexterity of a mechanical arm.

"I can't imagine how we could have berthed Intelsat 6 to the solid fuel booster without the manipulator arm," says astronaut Rick Hieb. For the type of missions NASA is planning, the arm is essential, he says.

Spar Aerospace, under contract to the National Research Council of Canada, developed the Shuttle Remote Manipulator Arm or Canadarm as part of the Canadian Space Agency's contribution to the shuttle program. The company has built five robot arms for NASA.

Crew members control the arm by adjusting the pitch of a handle, typing coordinates onto a keyboard, or selecting trajectories from the memory of an on-board computer. They can manipulate payloads the mass of a loaded school bus or retrieve a satellite the size of a model airplane.

Like the human arm, Canadarm has joints that rotate at the shoulder, elbow, and wrist. The arm is made of electric motors, graphite fiber beams, and copper wire. Three cables and a rotating ring, which opens and closes like the iris of a camera, replicate the hand. Astronauts can grasp an object floating in space without considering the movement of the arm's individual joints.

"With this program, Canada has become the leader in space robotics," says Garry Lindberg, vice president of Research and Development for the Canadian Space Agency. "We intend to maintain that reputation for excellence in the years to come."

As Spar engineers grow more confident, they plan robots that can cross space station trusses to repair an errant cooling system or dock an incoming shuttle.

NASA has scheduled shuttle flights to assemble the Freedom space station beginning in late 1995. The space agency estimates that 17 flights over four years will be needed. NASA collaborated with European, Japanese, and Canadian space agencies to design the space station. Member nations will build laboratories to manufacture alloys, crystals, and pharmaceuticals in space. The station will be a staging area for astronomical observations and expeditions that cross the solar system.

For Canada's part, Spar Aerospace is creating a 16-by-16-foot pallet called the Mobile Servicing Centre. The shuttle will transport the pallet to a platform 310 miles above the Earth where it will assemble and maintain the space station.

The Mobile Servicing Centre will move equipment and supplies across the platform, capture and release satellites, cradle astronauts servicing instruments attached to the outside of the space station, and tether the space shuttle to Freedom while it loads and unloads the shuttle.

The mainstay of the unit is a mechanical arm about the size of Canadarm but three times as strong. (Engineers have added a second wrist joint and hand to the original design.) It will free itself from its movable base, and crawl hand-over-hand across 500-foot trusses to service hard-to-reach equipment. Sensors will measure the force a robot hand applies to the surface of the space station and attached cameras can track objects in space.

A second robot called the Special Purpose Dextrous Manipulator will handle delicate work such as maintaining electrical circuits, cooling systems, and fuel lines. The robot will have two arms with up to 19 joints, giving it exceptional dexterity. The robots can work alone or as companions by connecting to one to another.

NASA planners have scheduled the arm to fly aboard the third shuttle flight to assemble the space station, which should occur during 1996.

It would be almost impossible to build the space station using the current concept of on-orbit assembly without the robot arm, says Don Pallesen, NASA's operations manager for Canadarm.