Solar power might actually be viable on Mars, despite its distance from the Sun (Image: Detlev Van Ravenswaay / SPL)
WHILE NASA's Phoenix lander slowly dies of power loss in the darkening Martian arctic, the space agency is weighing up the pros and cons of nuclear and solar power for a human mission to Mars.
Vocal protests accompanied the launch of the deep-space probes Cassini, Galileo and New Horizons, which all contained nuclear power generators, with anti-nuclear groups saying any disaster could rain radioactive debris on Earth. Off-planet colonies powered with fission reactors are likely to raise similar concerns.
The question is whether solar power can generate the 100 kilowatts that Martian explorers will need to power their life-support systems and to make the fuel needed for the journey back to Earth. To find out, NASA commissioned a study by energy specialists from the Massachusetts Institute of Technology.
It was generally thought that the sun's rays would be too weak on Mars to supply a significant amount of energy. However, the MIT team concludes that with a careful choice of location, solar energy can provide all the power a colony would need - even in the teeth of the Red Planet's infamous dust storms.
The team assessed 13 energy-generation systems, MIT engineer Wilfried Hofstetter told the International Astronautical Congress in Glasgow, UK, last month, comparing nuclear fission reactors, solar arrays that track the sun, non-tracking thin-film solar arrays laid on the Martian surface, and radioisotope thermal generators (RTGs), which use a decaying chunk of radioisotope to create heat that is used to generate electricity.
The MIT team's main aim, says Hofstetter, was to ensure that astronauts squeeze the most power from every kilogram of energy-generating equipment they take to Mars, but always have adequate back-up too.
While nuclear is the clear winner because it can produce a constant supply of power, a large solar array with fuel cells to store power matches its performance - but only if it is sited at a latitude between 0 and 40 degrees north of the Martian equator. "Southern latitudes have much less solar energy available most of the year," says Hofstetter.
Assuming a mission can take several 2-metre-wide rolls of thin-film solar panel material to Mars, a 100-metre by 100-metre surface array would provide the 100 kilowatts needed at 25 degrees north. The team calculates that it would take two crew members 17 hours to lay out the array and get it working, though robotic rollout is also a possibility.
Of course, Mars is no benign environment - dust storms are a major hazard and degrade solar arrays. But planetary scientist Colin Pillinger of the Open University in the UK says they shouldn't be a problem: "Dust storms tend to start in well-known places in the southern hemisphere as it warms up, so it shouldn't be too difficult to avoid them," he says.