(5645) 1990 SP is an Apollo-type near-Earth minor planet. It was discovered by Robert H. McNaught at the Siding Spring Observatory in Canberra, Australia, on September 20, 1990. Further observations of it was made by amateur astronomer Mohammed Alsunni of Sudan, that led to the refinement of its orbital calculations. (5645) 1990 SP makes close approaches to Mars and Earth. On 1969-Apr-14 the asteroid passed 0.0133 AU (1,990,000 km; 1,240,000 mi) from Mars. With an absolute magnitude of 17.1, the asteroid is about 1–2 km in diameter.