二、前言地球引力场近似为中心力场,人造卫星围绕地球运行时,其轨道平面经过地心。因而,卫星不可能在高纬度地区上空作小圆运动。然而,由于地球自转,选择适当的轨道要素,就有可能使卫星在包含赤道在内的局部地区上空作逗留运动,这时其星下点轨迹犹如小圆曲 II. Preface The Earth’s gravitational field is approximately the central force field. When the orbiting satellite is running around the Earth, the orbital plane passes through the geocentric center. Therefore, it is impossible for satellites to make small circular motion over high latitudes. However, due to the rotation of the Earth, the choice of appropriate orbital elements makes it possible for the satellites to stay in motion over parts of the Earth including the equator, in which case the trajectory of their stars is like a small circular curve