 Transit-9 and 5B4 (1964) and Transit-5B7 and 5B6 (1965) each had "a nuclear power source".The US Air Force also periodically launched short lived satellites equipped with radio beacons of 162 MHz and 324 MHz at much lower orbits to study orbital drag.The Transit ground tracking stations tracked these satellites as well, locating the satellites within their orbits using the same principles.