太阳同步轨道
Initial operations of early DMSP systems provided radio return of cloud-cover imagery for planning of U.S. high-resolution photographic reconnaissance and surveillance missions, which utilized film-return systems. DMSP satellites operated in a Sun-synchronous orbit; passing over the north and south poles, the satellite would see different strips of the Earth at the same local time each day. The DMSP satellites had periods of roughly 101.0 minutes, so they would orbit the Earth 14.3 times in 24 hours. This period combined with the Sun-synchronous orbit would have the satellite pass over the whole surface of the planet twice a day.