My Battery is Getting Low and it is Getting Dark

Ally Winning, European Editor, PSD



These were supposedly the last words sent back from Mars by the Opportunity rover. As we all know, machines don’t really communicate with such clarity and emotion, but it seemed a fitting farewell, and actually pretty well-deserved after seeing out its original mission objective of 90 days operation by over 14 years. Opportunity was always meant to be expendable, but the fact that the rover lasted so long in such a hostile environment is a testament to the abilities of the engineers at NASA.

Opportunity wasn’t the first rover to land on Mars. It was actually the fifth. The first two were actually sent by Russia in 1971. The first rover failed on contact and the second only survived 20 seconds after landing. It wasn’t even the first of its particular design, by being beaten to the surface of the red planet by its twin, Spirit, by three weeks. Spirit landed on January 4th, 2004 and operated until March 2010. Opportunity landed on January 21st 2004 and last communicated with earth in June last year. Both rovers had the mission objective of looking for water on Mars, which would in turn pave the way for human missions and help the search for extraterrestrial life.

Both Opportunity and Spirit were powered by a solar panel that could provide up to 900 Watts to two rechargeable Li-ion batteries, each with 8 cells with 8A-hour capacity. The batteries drove an electric motor on each wheel and power the rover’s sensor systems and other electronics. During Opportunity’s time on Mars, the rover covered nearly 43 km in total, including inclines of over 30o. Opportunity’s 14 year run came to an end during a dust storm, which coated its solar panels and stopped the batteries from recharging. It wasn’t the first fault to hit the rover, 4 years ago it had a problem writing telemetry data to its non-volatile memory. NASA managed to overcome by bypassing the broken memory bank and writing the information directly to the vehicle’s RAM.

The end of Opportunity is not the end of Mars exploration. While there are plans in design to send humans to live there in the future, currently the Curiosity rover is still alive and kicking on the Mars surface. Curiosity has been there since November 2011 carrying out a similar mission to Opportunity. Instead of operating using the power of the sun, Curiosity is powered by a radioisotope thermoelectric generator (RTG), which produces heat from the decay of radioactive isotopes, which is then turned into electrical power using thermocouples. The power system also dual functions as a heating system, with the waste heat used to keep the rover’s systems from getting too cold. Hopefully it will send back much more information before its own battery goes dark.