Viking was Sweden's first satellite. It was launched on an Ariane 1 rocket as a piggyback payload together with the French satellite SPOT 1, on February 22, 1986. Operations ended on May 12, 1987. Viking was used to explore plasma processes in the magnetosphere and the ionosphere. Space was limited underneath SPOT, and the satellite had to be sturdy to withstand the stress of launch. The basic shape of the Swedish satellite was a flat octagonal disc, only 0.5 meters thick and 1.9 meters across. The mechanical interface of the payload adapter from the Ariane rocket was duplicated on top of Viking. That enabled it to be carried with a minimum of redesign of the SPOT program. After SPOT had been released Viking fired its own rocket engine and was sent into a different polar orbit. Once in orbit, 4 wire segments of 40 meter length each were spooled out in a radial direction from the edge of the spinning satellite disc. Also, 2 stiff rods of 4 meter length were extended in the axial direction. A sensor pod was held at the end of each of these, forming three orthogonal pairs. Together they could measure the electric field in all three dimensions. Stiff booms were also extended for other types of sensors and antennas.
