US-A (Upravlenniye Sputnik Aktivny) were active radar satellites for ocean surveillance. The high power consumtion of the active radar required a nuclear reactor as power source. The satellites were known as RORSAT in the west. The US-AO series consisted of satellites, which tested all the system components but the nuclear reactor. They were battery powered.
Low Earth OrbitPioneer A to E (Pioneer 6 to 9 after launch) were a series of five solar-orbiting, spin-stabilized, solar-cell and battery-powered satellites designed to obtain measurements of interplanetary phenomena from widely separated points in space on a continuing basis.
Heliocentric N/A