Juno is the first US deep space probe not to use Radioisotope Thermal Generators (RTGs) for power generation (RTGs convert the heat generated
by the radioactive decay of plutonium to electrical power). Instead Juno will use solar arrays, despite the fact that solar power flux at Jupiter is 25 times less than that at Earth orbit. Looking at the pictures of the spacecraft the array area is of the order of 55 square meters (which is large), which will provide about 400 W of electrical power at Jupiter to operate the spacecraft. Because of the low solar intensity, the arrays will get cold at Jupiter orbit, which will help boost their generating efficiency. Some media agencies claim that this is the first spacecraft to use solar arrays at this distance from the Sun – but of course the Europeans have beaten them to it with the Rosetta spacecraft, which will operate with arrays at distances slightly greater from the Sun than Juno.
The mission will follow-on from the Galileo Jupiter orbiter (launched in September 1995), but it seems the focus of the mission will be more to do with studying Jupiter itself, and its magnetic and trapped radiation
fields. It is hoped to discover the internal structure of the planet. By contrast, much of Galileo’s objectives focussed on the characteristics of Jupiter’s many moons.