First humanoid Robonaut reaches the International Space Station

Semi-autonomous robots are on duty throughout the solar system – but one passenger aboard Nasa's STS-133 may just ignite the popular imagination.

It may seem like some sort of science-fiction scenario, but clever robots are scattered widely across the vastness of our solar system. All deep-space probes and planetary landers are capable of operating semi-autonomously in order to cope with the long time-lags between radio commands from Earth. Some, such as Nasa's wheeled Mars rovers, also boast certain degrees of mechanical flexibility provided via pan-and-tilt camera arrays, directable radio antennas, steerable wheels, extendable soil-sampling arms and other instruments.

The public perhaps struggles with the idea that these clunky boxes are definable as robots, but no one will be in any doubt about Nasa's latest non-human space explorer.

At first glance it looks just like an astronaut in a space suit. Even at second glance, it seems at least as lively as a 'Star Wars' character in an armoured mask. Its head is shaped somewhat like a motorcycle helmet, but its torso and arms, tipped by elegant hands with slender fingers and opposable thumbs, look very like our own.

Robonaut, the first humanoid robot ever sent into space, has just arrived at the International Space Station aboard space shuttle Discovery, as part of the payload for the STS-133 mission. It was stowed for launch inside the European-built Leonardo cargo supply module, which is now docked permanently on the station to provide yet more pressurised working volume.

In the coming months, the robot will be unpacked from its crate and repositioned inside the larger Destiny laboratory module. Although its primary task, for now, is to remain aboard the station while undergoing further tests, it will eventually be deployed outside the pressurised shell of the orbiting platform, where it will assist human space walkers in assembly and maintenance tasks.

This flightworthy version of the hardware is a second-generation machine, based on a prototype developed by Nasa and the Defense Advanced Research Project Agency (DARPA) over the last decade, and now coming to fruition via a joint project between Nasa, General Motors (GM), and Houston-based Oceaneering Space Systems. Special legislation allows all three partners to protect their joint intellectual property in a technology that could have far-reaching implications on Earth as well as in orbit.

According to Alan Taub, GM's vice president for global research and development, 'For us, this is about safer cars and safer manufacturing techniques right here on the ground.'

It is also about the future of a faltering US industrial giant as it looks towards new and post-petroleum automotive technologies. Assembly lines in the Far East harness the productivity of the world's most advanced robotic assembly systems. GM wants to see 'advanced robots working together in harmony with people, building better, higher-quality vehicles in a more competitive environment.' Robonaut is a high-profile testbed for some of these ambitions.

Hand and body

Robonaut is designed to look and behave much like a space-suited human, with no unexpected protuberances or sharp edges. When it drifts in and out of the limited peripheral vision afforded by an astronaut's helmet visor, it will seem perfectly familiar. Just as importantly, its physical gestures will mimic the behaviours that an astronaut might expect from a human colleague.

According to Dr Robert Ambrose, chief of the Software, Robotics and Simulation Division at Nasa's Johnson Space Center (JSC) in Houston, 'It operates at a speed and scale similar to us.' He clarifies this by pointing out that no robot yet built can truly meet that description. Nasa has set the bar slightly lower, in terms of 'the somewhat reduced dexterity, work envelope and performance of a human in a bulky space suit'.

In fact, Robonaut's grasping skills and sensitivity to touch are markedly finer than those of a space-walking astronaut, because its slender fingers have no need for thick gloves. A set of 14 brushless motors in each forearm drive the hands, each of which has the proper complement of four fingers and an opposable thumb, ensuring compatibility with all the tools designed for astronauts.

Robonaut can pick up a small metal washer with tweezers, and has the strength to lift more than nine kilos in weight. This may not sound like much, but it is more than sufficient for the inertial loads that it will encounter in the weightlessness of space. The two fingers furtherst from the thumb are designed just for grasping, while the thumbs, forefingers and middle fingers are more fully dextrous. The palm is also jointed.

Robonaut's gold-plated head is articulated at the neck, allowing a similar freedom of movement to a human head. The torso is built from aluminium, with Kevlar and Teflon padding to protect it from fire and micrometeorite impacts. The torso and arms are covered with a custom-fitted fabric skin that secures the electrical wire harnesses and keeps dust away from the mechanical joints. An inner layer of foam padding absorbs the impact energy of minor and permissible collisions between Robonaut and its astronaut companions.

Finally, we come to the lower extremities. The torso tapers neatly into the top of a single leg, with hip, knee and ankle joints. The 'foot' is an adaptor that clicks into various attachment points on the outside of the space station, or on the end of long and similarly articulated robotic boom arms that are already part of the station's external equipment. Swapping between available handholds and leg attach points, Robonaut will clamber from one secure location to the next, covering ground, so to speak, as it makes its way from one end to the other of the sprawling complex, but without ever completely letting go. It has no thruster packs or independent free-flying capability.

Laws of Robonautics

The common industrial practice of having a workplace robot cease all motion if anyone inadvertently touches it is not always appropriate for Robonaut, because it must be capable of interacting physically with astronauts without necessarily coming to a stop every time one of them bumps into it. In particular, it has to distinguish between dangerous collisions and desirable physical interactions when tools are passed from robot to human hands, or when the load of a particularly large piece of hardware is shared between the robot's grip and an astronaut's. Ambrose says that indicator lights and other cues will ensure that Robonaut's human minders will always have 'a general understanding of what state the robot is in.'

These states are analysed, in part, with the help of force-feedback sensors. But Robonaut can also see what it is doing. Its head contains four stereoscopic cameras, one pair in standard definition and the other in HD. This enables the machine to build a depth map of nearby objects, which assists in collision avoidance as well as in the performance of its assembly tasks.

Robonaut's hazard assessment is loosely comparable to the famous 'Laws of Robotics' proposed by the science fiction writer Isaac Asimov some half a century ago. In simple terms, an Asimovian robot has freedom of action unless the proposed action threatens to cause harm to a human.

Similarly, Robonaut operates a hierarchy of 'sub-autonomies', with harm avoidance at the top of the pyramid. Various sub-autonomies run motion control in 3D Cartesian space, the vision system, the teleoperator interface, joint control, and grasping actions. Each sub-autonomy deals with its own internal safety and decision making, but will 'request' rather than 'demand' a reconfiguration, or even a complete safety shutdown, if it senses trouble. Higher level software then monitors potential conflicts between the sub-autonomies and compares them with safety parameters before allowing or disallowing certain tasks.

All this is accomplished by PowerPC processors running VxWorks, and wired to a Virtual Machine Environment (VME) backplane, or motherboard, inside Robonaut's torso. VME allows the sharing of the underlying machine resources between different virtual machines, each running its own operating system.

The object-oriented ControlShell software framework is used to aid the overall development process, which will continue throughout Robonaut's operational life.

The puppet master

Ron Diftler, Robonaut project manager at JSC, speaks proudly about these capabilities. 'Here's a robot that can see the objects it's going after, feel the surrounding environment and adjust to circumstances as needed. That's pretty human. 'It opens up endless possibilities.'

On the evidence of such a description, Robonaut sounds suspiciously smart. If its actions and intelligent behaviour seem almost spookily human, this is because they really are human. Despite its semi-autonomous capabilities, it is essentially an avatar, driven by a human operator inside the space station, or down on the ground.

A stereo vision helmet allied to a force feedback endoskeleton and a pair of gloves studded with haptic sensors enables the operator to see and even to feel Robonaut's environment. The system is an advanced form of what's known as 'telepresence'. The application programmer's interface (API) allows more than 40 degrees of freedom to be controlled remotely in a 'master-slave' relationship where the operator's motions are mimicked, in near real-time, by the robot.

A key factor in the API's design is ease of use for the human operator. Nasa likes to design its control systems with the human-machine interface at the forefront of its thinking. Astronauts tend to have backgrounds in military aviation or aerospace engineering, with biological and space sciences also adding to the selection mix. Relatively few of them are professionally familiar with computers or robotics. They need to operate the Robonaut without having to know too much about its internal systems. Manipulation of the system must becomes as intuitive as performing the machine's tasks oneself.

Could it be that Robonaut and his kind will one day supplant humans in space? John Olson, director of the Exploration Systems Integration Office at Nasa's headquarters in Washington, DC, says that such a mournful outcome would be the very opposite of his agency's intentions. 'This project exemplifies the fact that robots are not replacements for us, but companions that can carry out key supporting roles alongside us,' he says.

The combined potential of humans and robots is, Olson believes, 'a perfect example of the sum equalling more than the parts. It will allow us to go farther and achieve more than we can probably even imagine today.'

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