The Juno spacecraft in front of Jupiter. Juno is one of the largest planetary spacecraft to ever be launched
Built by Lockheed-Martin, the Juno spacecraft's heritage of successful
design features insure achievement of the mission science objectives.
Like earlier Pioneer missions, Juno utilizes a spinning spacecraft to
investigate the giant planet. The spin rate of the spacecraft is expected
to be between 2 and 5 revolutions per minute, providing plenty of pointing
stability, while also functioning as its own gyroscope!
Unlike earlier missions such as the Pioneers, Voyagers, Ulysses, Galileo and Cassini, Juno uses three solar panels 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 Thermal Generation (RTG) power.
The amount of sunlight available to generate power for a spacecraft exploring the outer planets is about twenty seven times weaker, as compared to that of a spacecraft exploring the inner solar system. 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, ~2 m x 9 m 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 are folded into four hinged segments so that the spacecraft can fit into the spacecraft faring. The high gain antenna is attached to the center of the main hexagonal body of the spacecraft, which safely protects the engineering systems and science instruments from Jupiter's regions of high radiation.
An oblique view of the Juno spacecraft shows the three solar panels, one of which carries the magnetometer (yellow extension on the upper solar panel in this image). The main body of the spacecraft is underneath the high gain antenna, which is used for communications to Earth. The three solar panels are built in four-hinged sections that allow the spacecraft to fit within the rocket for launch. A human figure in this picture gives an approximate idea of the size of the spacecraft.
End to end, the spacecraft and panels, cover a circle more than 20 meters in diameter. At the end of one of the solar panels a wire magnetometer extends nearly two meters. The parabolic high gain antenna directs a narrow radio beam of spacecraft communications towards the earth and the spacecraft spins about this axis, occasionally turning slightly away to collect observations from the Microwave Radiometer.