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Solar power and JUICE’s massive panels

On its way to Jupiter, JUICE is moving away from the Sun. Sunlight is getting fainter and fainter, which becomes a problem if your spacecraft’s electronics is designed to be powered by solar energy. Solution: massive solar panels. Juno, a NASA mission, had the previous record of solar panel area. JUICE now holds the record.

This graphic shows how NASA’s Juno mission to Jupiter became the most distant solar-powered explorer and influenced the future of space exploration powered by the sun. Credits: NASA/JPL-Caltech/

Each of JUICE’s panels measures about 2.5 m by 3.5 m, and there are five on each side of the spacecraft. The total sun-collecting area is about 85 square metres. To fit inside the rocket that sent JUICE into space, the panels had to be folded. After launch, they were deploy into two distinctive cross-like formations.

The solar panels have to survive an insane range of temperatures, from +110 C as JUICE flies by Venus down to negative 230 C once arrived in the Jupiter system. The temperature will also suffer quick oscillations. At Jupiter, when the spacecraft is temporarily eclipsed by the giant planet and the moons, it receives no sunlight and the solar panels cool very rapidly. Furthermore, the solar panels will be subjected to a harsh radiation environment. Extensive testing was carried out to ensure the solar arrays can survive these very difficult conditions.

JUICE's solar panels are key to explore Jupiter and Ganymede. Credit: ESA

As mentioned at the top, the Sun is very once you reach Jupiter. While the solar power we receive at Earth is about 1360 watts per square meter, at Jupiter it is only 50 watts. But how do solar panels work to convert this solar power into electricity?

Solar panels work using the photoelectric effect, which was discovered by Albert Einstein. Famous for his relativity theory and for the E=mc2 equation, Albert actually received his Nobel Prize in 1921 for the discovery of the photoelectric effect. It is deserved, because it is thanks to this discovery that we are now able to harvest so much energy from the Sun to start replacing fossil fuels. The photoelectric effect works as light photons hit electrons in a metal or semiconductor and liberate them to form an electric current.

Photoelectric effect. Credit: Wikipedia article on photoelectric effect.

Given the meagre solar power available at Jupiter, the JUICE mission solar panels needed a boost. While silicon was once the semiconductor of choice to build solar panels, JUICE uses gallium arsenide (GaAs). Gallium-arsenide panels are 1.5 times more efficient than the ones used in previous ESA mission, like the Rosetta mission to comet 67P.

Solar panel research is very important as we keep moving towards using only renewable energy on Earth. This is also true if we are going to have permanent human settlements in orbit, on the Moon, or on Mars. The Sun is always bathing us in a shower of energy and all we have to do is catch it as efficiently as possible.

Artist impression of a Moon Base concept. Credit: ESA – P. Carril

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