Canadian robot Dextre sets off on a space adventure

As Space Shuttle Endeavour rocketed into space at 2:28 a.m. ET on Tuesday from Kennedy Space Center in Florida, the offices of Brampton, Ont.-based MDA Ltd. were dark and quiet – despite their latest creation being carried to the International Space Station.

It’s not because they don’t care.

But for the robotics company that also created the robotic arm installed on the space station, the exciting part comes when astronauts haul the Special Purpose Dexterous Manipulator (Dextre) out into orbit 250 miles above Earth.

That moment will come Friday, when mission specialists Rick Linnehan and Garrett Reisman from the STS-123 crew embark on a spacewalk to begin work on Dextre.

“There’s a real excitement to see it assembled from orbit,” says David Gordon, senior engineer of mission systems at MDA. “You could call it the next generation of robotics.”

The first spacewalk will install gripping tools on to the end of Dextre’s arms.

It will take several more outer space jaunts before the robot can be transferred to the station’s Mobile Servicing System, according to Daniel Lefebvre, systems engineer at the St. Hubert, Que.-based Canadian Space Agency (CSA).

Once there, “we’ll know that it’s nice and warm and cozy and [we’ll have information] on the basic health of the robot,” he says. Power and data commands can also be delivered at that point.

The 1,560 kg robot will be assembled for the first time in orbit – it can’t support its own weight on Earth.

When it’s finished, the two-armed robot will have a reach of almost 3.5 meters, according to a CSA spec sheet.

Dextre’s arms connect to the robot’s upper body. Each arm has seven joints to give it great freedom of movement (just imagine having seven elbows.)

Below the bendable and rotating waist, a lower sports a utility belt with a variety of robotic tools. Video equipment, lights, and umbilical connectors supplying power and data cling to Dextre.

Zero-gravity software simulation

“One of the unique things we had to face is because the arms of Dextre are designed to operate in zero-gravity, they can’t support their own weight on the ground,” Gordon says.

That means computer simulation had to take the place of reality. Aside from limited testing done with Dextre suspended from pulleys and cables like a giant mobile, most test work was simulated.

“We developed a very sophisticated simulator that could model the motion of the joints, the friction, and all these things the hardware would normally be relating back to the software,” Gordon explains.

Doing a hi-fidelity job of simulating the complex robot was crucial for astronauts to know what to expect from its operation in outer space.

The two-week training course instructing Dextre’s use has only been completed by 11 astronauts so far.

Building a robot from the ground up

At the John H. Chapman Space Centre in Longueuil, Que. the CSA now trains soon-to-be Dextre operators. The course is in addition to another two-week program instructing use of the Canadarm2 and the Mobile Servicing System (also built by MDA).

The simulator makes use of MDA’s actual software that controls Dextre, and emulates some of the hardware components, Lefebvre says. All the motherboards for the electronic components are used in simulations, for instance.

For astronauts using the simulator, “you’ve got a 3D representation of the space station… as well as Dextre and some of the payloads they’ll have to manipulate,” he says.

Images piped back to Earth from NASA during the mission will show how complex the operation of the robotics can be when Candarm2 is used to install Dextre, says Joe Edwards, client executive for EDS U.S. Government Solutions and former NASA shuttle pilot.

“Because the training is so extensive and requires such attention to detail and knowledge of the system, not every astronaut is trained in operation of the robotic arms,” he says.

Astronauts control Dextre by sending commands to two redundant computers that manage 21 lower-level robots distributed across the robot’s body, explains Gordon.

The software used to coordinate motion throughout Dextre, Candarm2, and the mobile station is now up to 1.5 million lines of code.

“We test each piece of software completely on its own, in isolation,” Gordon says. “We make sure all the lower level computers can interact properly with the main computer on Dextre.”

Dextre’s use is not limited to astronauts on board the orbital outpost.

Mission control in Houston, Texas is also able to control the robot remotely. The signal is sent through the pipeline that most of the space station’s communications flow through – two satellites 22,000 miles above Earth.

From the Tracking Data and Relay Satellites that take turns supplying communication with ISS as it rotates the globe every 90 minutes, the commands are sent to Dextre as though coming from an astronaut at the control panel, Edwards says.

“The computer doesn’t care if those signals come from the ground or from an astronaut operator,” he explains. “In the end what you’re really sending to that device are ones and zeros – binary computer commands.”

Ground control is practically transparent to Dextre’s software, Gordon agrees.

All control panels are similar, with three monitors displaying views from the robot’s cameras, a selection of switches and buttons, and an interface for a laptop to connect and deliver commands with a GUI.

“On the GUI they have a schematic of Dextre,” Gordon adds. “In various fields, it would show the current position of the joints and whether the grippers are open or closed.”

Robot with a human touch

The grippers Gordon refers to are Dextre’s hands – the orbital replacement unit/tool change out mechanism that is essentially a retractable motorized multi-tool that can turn bolts and manipulate objects. Parallel jaws hold the desired tool or payload in a vice grip.

Since Dextre is intended for use in missions that were previously only accomplished by a risky spacewalk, accuracy is important.

Able to apply up to a powerful 600 kg of force, Dextre also has a fine touch. It can target its component with 6 mm accuracy and adjust the force it applies within 2.2 newtons – a feather’s touch.

“When a force is applied [to] the tip of the arm that translates into a particular voltage and [is] fed back into the control system,” Gordon says.

A computer dedicated to each tool at the arm’s end applies the specific voltage to the gripper motor and then receives the feedback to sense how firmly the grip is held. If alignment is a bit off, joints are moved to compensate.

 “It’s really the same sort of thing that would go on in your body. Your brain interprets forces you feel and causes your hand to move a little bit to the right or the left,” the engineer adds.

From outer space to the operating room

Dextre is on its way to live in space. But other homes have already been found for the same robotic technology MDA developed for the space station. Like many other space innovations, it has found a use here on Earth.

“It’s almost impossible in this highly technologically advanced world we live in to separate ourselves, even in our most mundane tasks, from the space program and the research that has gone into it,” Edwards says.

Everything from cordless power tools developed for the Apollo program to weather data beamed down from telecommunications satellites come thanks to space-related research, the former astronaut continues.

In the medical field, digital signal processing developed for Apollo communications has been parlayed into magnetic resonance imaging (MRI) technology. MDA’s technology has also found a place at home in a medical lab.

“We built a medical robot for the University of Calgary,” says Lynne Vanin, manager of public affairs at MDA. “It’s arms, it doesn’t have the body.”

Dubbed NeuroArm, the robotic apparatus could be controlled by a neurosurgeon remotely to perform incredibly precise operations on the brain. It is scheduled to arrive in the university’s operating room today, according to the school’s Web site.

Built out of ceramic materials so it could be used during an MRI scan, NeuroArm will begin clinical trials. It could eventually be used to remove brain tumours and blood clots.

“Even slight tremors in the surgeons’ hands can have negative impact on the patient,” Vanin says. “The force movement sensing takes any movement out of the tip of the arm.”

Meanwhile, MDA will be busy completing the final piece of the puzzle for their contributions towards the world’s outer space science laboratory. They were awarded a $7 million contract from NASA on Feb. 15 to develop an enhanced platform for Dextre to sit on.

It will replace the temporary platform Dextre is installed on during the current mission, Vanin says. “It’s a little more sophisticated.”

NASA’s current schedule has that mission slated to launch in 2010. The exact date is sure to be one circled on the calendars of MDA engineers, so they can see the last component of their robotic system assembled in the vastness of space.

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