Mars Exploration Rovers - Opportunity Awaits!

Mars Exploration Rovers - Opportunity Awaits!

History

NASA’s exploration of Mars has been ongoing since the 1960’s.  The Mariner program performed the first successful flybys and orbits of Mars in the late 60’s and early 70’s.  The Viking program succeeded in sending two landers and orbiters simultaneously in the mid 70’s.  In 1997, the Pathfinder succeeded in landing a rover on the Martian surface while being more economically feasible than the previous Viking missions ($280 million vs. $3.5 Billion 1997 dollars).  It also validated concepts that would be used by later missions, such as airbag-mediated landing and automated avoidance.

The exploration of Mars continues today with the recent and ongoing success of two mars exploration rovers, Spirit and Opportunity. Their main science goal is to examine local geology for evidence of past water activity.   Both landed on Mars in 2004 and while Spirit was recently named a stationary research platform in January 2010, Opportunity continues to explore the Martian surface more than six years after its touchdown. To date Opportunity has covered over 27.82 Km (17.29 miles), well over the projected 600 m.  The continued success of Opportunity is a testament to the hard work of NASA researchers and engineers

Artist Depiction of Spirit and Opportunity Exploration Rovers

Source: wikipedia

 The rovers have a solar array over it WEB and two solar wings.  Two Hazcams are located on the front and back each.  Two Navcams and Pancams rise from the mast, giving each the ability to create stereo views.  A mechanical arm sits on the front of the rover, with a microscopic camera and rock abrasion tool attached.

Electronics

So what makes Opportunity so successful? The core of this rover is rover contains the rover electronic module (REM), which is designed to survive the harsh condition of the Martian surface, as well as space.  The on board computers and wiring can tolerate temperatures with the range of -40 ˚C to 40˚C, and are radiation hardened. They also are resistant to memory loss or errors during the cyclical operating schedule.  Meanwhile, they still have the processing power of a high end laptop and memory of a standard home computer by 2004 standards. 

A warm electronics box (WEB) protects the REM from the harsh Martian atmosphere, which can dip to   -96˚C.  The walls of the box are insulated with gold paint and aerogel.  Excess heat from electronics and radioisotopic heater units (RHUs) provide the majority of heat in the WEB.  RHUs continually produce about 1 watt of heat through the decay of a low grade isotope.  This is crucial, because it reduces the amount of energy used on electronic heaters that are also contained in the WEB.  Excess heat generated by the electronics when the rover is cruising can pose a threat to the REM.  In this case, a heat rejection system pumps CFC-12, a fluid similar to Freon, through the WEB to absorb excess heat.  This pump operates similar to a cars air conditioner, and can shuttle 150 watts of rover waste heat out of the WEB.

Energy

The rover generates energy using solar panel wings and is equipped with two rechargeable batteries.  It was expected to generate 140 watts during a sol (Martian day), with that number slowly dropping over time due to dust covering the panels.  Unexpected cleaning events have allowed the energy generation to remain at reasonably high levels throughout the mission.   The rover requires around 100 watts per drive to drive, and it also must maintain acceptable internal temperatures during the Martian night in order to protect its vital instruments. 

Mobility

The rovers have six wheels, each with an individual motor.  The front two and back two wheels also have their own independent steering motors, giving the rover an ability to turn 360 degrees in place.  Rocker-bogie suspension allows it to both swivel side to side and rock up and down.  Opportunity is designed to handle up to a 45 degree tilt, but the rover is programmed with hazard avoidance software to avoid tilts exceeding 30 degrees.  The rover has a top speed of 2 inches per second on flat hard ground.  However, hazard avoidance software forces the rover to stop every few seconds and reassess it environment.  

Communication

The Rover has 4 antennas that operate in low, medium and high gain frequencies, as well as UHF.  This gives the mission team multiple ways to communicate with the rover.  Communication can either be direct or it can be relayed through a craft orbiting Mars.  Communicating with orbiters saves energy because the rover doesn't have to "yell" as loud.  Also, satellites are in view for longer periods of time.  When direct communication occurs, lag time can be anywhere from 1.5 to 5 hours.  This requires mission team members to pre-plan routes for the rover, and rely on automated sensors, as well as hazard avoidance software.