Israeli calculations helped ‘Spirit’ and ‘Opportunity’ rovers land on Mars

Prof. Joseph Appelbaum of Tel Aviv University calculated that the diffused solar radiation existing on Mars would be sufficient to keep the solar panels functioning – even during dust storms. After the rovers ‘Spirit’ and ‘Opportunity’ landed on Mars in …

Prof. Joseph Appelbaum of Tel Aviv University calculated that the diffused solar radiation existing on Mars would be sufficient to keep the solar panels functioning – even during dust storms. After the rovers ‘Spirit’ and ‘Opportunity’ landed on Mars in January 2004, international excitement was so great that NASA received over 6.5 billion hits on its website in less than two months. Helping the wildly popular Mars program get off the ground, so to speak, were some calculations of an Israeli scientist, Prof. Joseph Appelbaum of Tel Aviv University, along with colleagues at NASA.

Appelbaum, a specialist in solar energy at TAU’s Fleischman Faculty of Engineering, determined the feasibility of using solar power for landers and rovers on the Martian surface. He also developed the solar radiation model that was used for the design of the photovoltaic arrays for the first Mars lander ‘Pathfinder’ in 1997, and for Spirit and Opportunity, and for possible future missions to Mars.


Back in the late 1980s, when NASA started planning its Mars program, the agency was looking for a long-lasting power source for possible landers and rovers.

Solar power was initially dismissed because no one believed there was enough solar radiation on Mars, and even if there were, it was feared that photovoltaic cells would get clogged by dust during one of Mars’ infamous dust storms, rendering the solar panels useless.

Instead, NASA was thinking of using a radioisotope thermal generator – essentially a small, nuclear-powered device. Such a generator already existed but was not powerful enough for a mission on Mars. It would take time and a sizable budget to bring designs for a more powerful device to the implementation stage.

This is where Appelbaum came in. Based on his calculations of solar radiation on Mars, together with data on dust particles and atmospheric gases in the Martian atmosphere, Appelbaum concluded that there was enough solar energy to overcome harsh conditions and power the landers and rovers.

While it was true that the sun’s direct beam would be attenuated by dust storms, Appelbaum calculated that the diffused solar radiation existing on Mars would be sufficient to keep the solar panels functioning – even during dust storms.

Appelbaum developed a complete mathematical model for solar energy on Mars at any given time, day and site. “It took some time to convince people at NASA that my model would work,” he said, “but eventually they adopted it.”

A team at the Jet Propulsion Laboratory (JPL) of NASA used the model to design the solar panels for Pathfinder, which landed on Mars in 1997. Planned to work for 30 days, the power source ended up functioning for almost 80.

Designs for the Spirit and Opportunity solar panels were based on the same solar radiation model, which has proved a boon for space research by harnessing a ready source of energy with available and inexpensive technology.

(Courtesy of Tel Aviv University News)