Solar Panels
Juno is the first mission to Jupiter using solar panels instead of the radioisotope thermoelectric generators (RTGs) used by Pioneer 10, Pioneer 11, the Voyager program, Cassini–Huygens, and the Galileo orbiter. Once in orbit around Jupiter, Juno will receive 4% as much sunlight as we do on Earth, but advances made in both solar cell technology and efficiency over the past several decades makes it economically feasible to use solar panels of practical size to provide power at a distance of 5 AU from the Sun.
The Juno spacecraft uses three solar arrays symmetrically arranged around the spacecraft, which were stowed against the sides of the spacecraft for launch. Shortly after the spacecraft cleared Earth's atmosphere the arrays were deployed. Two of the arrays have four hinged segments each, and the third array has three segments with a magnetometer in place of the fourth segment. Each panel or array is 2.7 meters (8.9 ft), by 8.9 meters (29 ft) long, the biggest on any NASA deep-space probe. One of the panels is slightly narrower than the others; this is to facilitate their stowage for launch. These smaller panels are 2.091 meters (6.86 ft) wide. The total area of the arrays is 60 square meters (650 sq ft). If the arrays were optimized to operate at Earth, they would produce 12 to 14 kilowatts of power. Only 486 W will be generated when Juno arrives at Jupiter, declining to 420 W as radiation degrades the cells. The solar panels will remain in sunlight continuously from launch through to the end of the mission, except for short periods during the operation of the main engine.
A central power distribution and drive unit monitors the power that is generated by the solar arrays, distributes it to instruments, heaters and experiment sensors as well as batteries that are charged when excess power is available. Two 55 amp-hour lithium-ion batteries will provide power to the vehicle when it passes through eclipse. Those batteries will be able to withstand the radiation environment of Jupiter.
Read more about this topic: Juno (spacecraft)
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