Hi Chris S.!

The Juno mission is a great example of how advances in technology can allow us to improve the performance of spacecraft. People may wonder why we are sending another mission to Jupiter, when Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Galileo, New Horizons, and Cassini have already visited Jupiter. Of these missions, Galileo was the only one to actually enter into orbit around Jupiter. The others were just passing by Jupiter on their way to complete other scientific goals. All of these missions used radioisotope thermoelectric generators for power.

In the years since these other missions were launched, there have been tremendous advances in spacecraft instrumentation and solar panel technology. The two big problems in sending a solar-powered spacecraft to Jupiter are its distance from the Sun and Jupiter's harsh radiation belt environment. Juno uses modern solar cells that are 50 percent more efficient and more radiation tolerant than the silicon solar cells available for space missions 20 years ago. The Juno mission has been carefully planned so that the spacecraft has a polar orbit that minimizes damaging exposure to Jupiter's radiation belts and will avoid eclipses by Jupiter so that all science measurements can be taken with the solar panels facing the sun. The three solar panels used on Juno are enormous and extend outward from the hexagonal spacecraft body to a span of about 66 feet (20 meters). For comparison, the Van Allen Probes mission to study the Earth's radiation belts has a span of only 10.5 ft (3.2) with the solar panels deployed.

Kris S.