Juno Spacecraft (Early Design Concept)
Like earlier Pioneer missions, Juno utilizes a spinning spacecraft to investigate the giant planet Jupiter. The spin rate of the spacecraft is generally revolutions per minute, providing plenty of pointing stability.
Unlike all earlier missions to visit Jupiter -- the Pioneers, Voyagers, Ulysses, Galileo, Cassini and New Horizons -- Juno uses solar arrays to generate electrical power for the spacecraft as well as its suite of scientific instruments. The innovative design of the Juno spacecraft to exploit solar power distinguishes Juno from those missions relying on radioisotope power.
The amount of sunlight available to generate power for a spacecraft exploring Jupiter is twenty seven times weaker than the power available at Earth. Thus, due to the much greater distance of Jupiter from the Sun, the surface area of solar panels required to generate adequate power must be much larger. The Juno spacecraft uses three approximately 2 meter x 9 meter solar panels that will remain in sunlight continuously from launch through end of mission, except for a 10-minute period during the earth flyby. Before launch, the three solar panels were folded into four hinged segments so that the spacecraft can fit into the rocket's payload faring.