What Can We Learn From Mars?
The Gusev Crater and Meridiani Planum on Mars are a long way from Silicon Valley, but just getting to those spots and digging around may help bring about technology breakthroughs on Earth, according to some engineers involved with the mission.
The Mars Exploration Rovers mission, in which a pair of six-wheeled rovers have gone to Mars to study the planet's makeup and look for evidence of water, is forcing engineers to deal with extraordinary conditions, not the least of which is the 106 million miles currently between the rovers' destination and mission controllers on Earth. However, the special demands of the months-long flight and the surface of Mars call for some capabilities that may be useful closer to home.
Among the many technologies that went into the missions are cutting-edge robotic capabilities and an embedded operating system that can, to some degree, take care of itself, say engineers who helped create the systems.
A New World
Development of the Mars rovers has helped break new ground for robotics on earth, according to Eric Baumgartner, a group supervisor in the mechanical and robotics technology group at the National Aeronautics and Space Administration Jet Propulsion Laboratory, in Pasadena, California.
Most robots on Earth are designed to operate in manmade environments such as factories, he says. These robots can be programmed ahead of time to know what the prepared setting looks like and how to operate within it. For example, a robot in an auto plant knows where the engine or body will appear on the assembly line and where it will need a weld.
The Mars rovers Spirit and Opportunity, on the other hand, bounced onto a whole new world.
"It's very different from the way robots are used on factory floors, and the primary difference is we're working in a totally unstructured and unknown environment," Baumgartner says.
"What's different about Mars is that we cannot ... fixture everything up and make sure everything's in the right spot," he says.
As a result, the rovers had to learn about their new home through their own sensors, including a set of nine cameras on each rover. Each rover has two navigation cameras for a 3D view of the surroundings, two hazard avoidance cameras for a 3D view of nearby terrain, and panoramic cameras to capture images of the planet's surface all around the rovers before they even leave their landers.
The rovers can't just look around them, process the images, and know where to go, Baumgartner says. Neither can the mission controllers grab a joystick on Earth, watch moving images from the cameras, and start steering the rovers. A key reason is processing power: The central processor in each rover, built to resist the extreme cold and radiation of Mars, has a top speed of 20 MHz. Instead, during the Martian night, while a rover is "asleep," a team on Earth with much more powerful computers programs its activities for the day ahead, then sends basic instructions on where to go and how to get there.
However, smaller decisions such as how to avoid small obstacles are up to the rovers themselves, Baumgartner says. Information from the hazard-avoidance cameras can help them analyze the immediate environment as they roll across the planet at a snail's pace--a maximum speed of 5 centimeters per second, with regular stops to check the terrain.
Along with taking pictures, each rover is examining the planet with several instruments on a robotic arm, designed by the team Baumgartner leads. The arms have "shoulder," "elbow," and "wrist" joints for maneuverability and are equipped with four sensors: a microscopic camera for close-up pictures of rocks, an alpha particle x-ray spectrometer for determining the mineral content of rocks, another spectrometer especially for detecting iron, and a rock abrasion tool for cutting through the layer of oxidation that forms on the surfaces of Martian rocks. As with the movements of the rovers, the arms are controlled mostly via prepared commands from mission control, with smaller movements gauged by the craft itself.
Lessons learned in the development of the rovers may pay off in two areas, Baumgartner says.
One possibility: A robotic arm that doesn't require real-time human control might be good for disabled people who use wheelchairs and can't control a joystick with their hands. Using its own sensors, it could reach out and get things for the person in the wheelchair, for example.
In addition, a robot that can deal with new and unknown environments might save manufacturers money. In current factories with robotic "workers," when the company shifts to making a new product, the whole factory floor has to be reconfigured and the robots reprogrammed to deal with the new arrangement. A robot that could use feedback from sensors to figure out where things are could adapt to changes by itself, saving the company the time and effort of building a new structured environment and reprogramming the robots, Baumgartner says.
An Earth-bound robot could be more autonomous because more powerful processors could be used so that more of the processing could take place rapidly in the robot itself.
Another mission technology that helps the craft operate millions of miles from their controllers is their operating system software. The OS, adapted by Wind River Systems from its VxWorks real-time embedded operating system, is built to travel. After all, in space or on Mars, you can't just hit the restart button if the OS reacts badly to something, as Wind River's Mike Deliman points out.
"Space is full of unexpected things," says Deliman, a member of Wind River's technical staff and chief engineer of the operating system for the Mars rovers. "When [Microsoft's] Windows encounters something it doesn't expect, you get a big blue screen. We can't afford to have that happen."
"You have to be able to characterize what the computers are going to do in any given situation," Deliman says.
The OS proved its worth on the way to Mars in October, when a solar flare of historic proportions occurred as Spirit and Opportunity both sped across space. The craft used "star tracker" cameras to automatically orient themselves in relation to the stars. The flare caused what looked to the cameras like flashes of light, temporarily confusing the systems, according to Deliman. The OS allowed mission control to turn off the star trackers until the solar storm had passed, then turn them back on, with no harm done.
"We had some conditions that were unanticipated, and since we knew how the computers would react under those conditions ... we knew exactly what kind of commands to send to deal with the situation," Deliman says.
The software on a spacecraft also needs to have intelligence built in to work around hardware failures, because the hardware can't be replaced, he says.
Fixing the Flaws
Deliman credits the flexibility of the OS with NASA's success in diagnosing an apparent memory problem that struck the Spirit rover as it explored the surface of Mars and led to a series of restarts. The OS was flexible enough to let the controllers try several possible solutions before the problem was solved, he says.
Lessons learned from space missions, many of which Wind River has been involved with, often come in handy on Earth, where the largest portion of the company's revenue comes from applications of its embedded operating system in networking equipment.
"Every single enhancement that we bring back from a project like Mars Rover we add to our code base, and it gets reviewed for addition into the mainline product," Deliman says.
For example, it's easier for engineers to reach a router than a spacecraft, but it may be expensive and time-consuming to do so when the router is in a carrier central office, and any down time could disrupt the network. An advancement such as figuring out how to make a Mars Rover work around a failed sensor can help developers write better router software for working around a failed memory chip. That may mean the router won't have to shut down, which prevents a network failure.
Space missions also force Wind River to make a more accurate and efficient operating system. For the current mission, Wind River enhanced some math routines to enable the craft to make highly accurate course corrections on the way to Mars. That saved further fine-tuning adjustments, all of which would have consumed precious fuel, he says.
For the teams involved in the Mars mission, dealing with the unknown and unexpected is all in a day's work. But like the Martian "sol," which is 39 minutes longer than a day on Earth, that day's work is likely to pay a dividend.