Why Have The Rovers Lasted So Long?
Living Beyond the Extended WarrantyWith a mission planned for 90 sols (martian days), the Mars Exploration Rovers Spirit and Opportunity passed their "warranty dates" by thousands of days! So, how have these rovers survived the rocky terrain, the frigid cold, and the wind-blown dust scouring the surface of Mars?
So why have the rover's lasted so long?A combination of sturdy construction, creative solutions for operating the rovers and even a little luck!
Built to be ToughEngineers designed the rovers' aluminum and titanium mobility systems to handle both the tough terrain of Mars and the wild temperature swings of up to 180 degrees Fahrenheit (100 degrees Celsius) each day.
Hard to Tip OverEach rover has six-wheel drive for getting around and a "rocker-bogie" suspension designed for stability. The center of gravity for the rover is at the pivot point, where the rocker-bogie attaches to the body. This design means the rover can tilt up to 45 degrees in any direction without toppling over.
Spreading the LoadA differential, a shaft that connects both sets of wheels, uses gears to spread the rover's weight across all six wheels. If the left side wheels tilt up, the right side presses down, providing the balance to all six wheels to get out of a sticky situation.
Keeping Warm When It's Really ColdInside the "belly" of each rover is a "warm electronics box" to keep batteries and other cold-sensitive equipment warm enough to keep working. Eight radioisotope heater units each produce about one watt of heat from about 2.7 grams (0.1 ounce) of plutonium dioxide.
Surviving the Cold NightsWith nighttime temperatures dipping as low as minus 157 degrees Fahrenheit (minus 105 degrees Celsius), the heaters have allowed the rovers to operate for years in the harsh martian cold.
Driving BackwardsTwo years into her mission, Spirit's right front wheel motor stopped. Pushing a stuck wheel across sandy soil was too hard. The best choice: drive backwards to take the pressure off. Spirit spent the rest of her over six-year mission driving backwards, dragging her front wheel.
Leaning Toward the LightBecause Mars is almost twice as far from the sun as Earth, less sunlight reaches the surface, even in the summer. The rovers needed more creative solutions to survive the especially gloomy Martian winters when even less sunlight was available for power.
Working in WinterParking for months on north-facing slopes both saved energy and allowed the dust-caked solar panels to be tilted toward the weak winter sun. With the small boost in power, the rovers could keep working while standing still.
Working While in 'Park' ModeIn 2006, for example, Spirit took 119 images to create a high-resolution panorama of her winter haven, resulting in the McMurdo Panorama that you see here.
Opportunity Loves 'Lily Pads'During its fourth martian winter, the Opportunity rover has been able to drive despite low amounts of sunlight. Engineers on Earth drive the rover from one small hill to another, called "lily pads," always keeping the solar panels tilted toward the sun.
A Panel DiscussionThe rovers' unique wing-shaped solar panels provide more surface area to collect the weak martian sunlight. That also means more area to get covered in the fine, reddish dust! Engineers expected some dust to accumulate on the panels.
Dust-Covered Solar PanelsAs the years passed, the rovers appeared to blend in with the landscape as the dust covered them. The amount of energy generated by the dusty panels declined.