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通过对万有引力知识的学习,我们知道,发射卫星的最小速度是(gR)~1/2(又称第一宇宙速度),此时卫星以最大速度绕地球表面作圆周运动;当发射速度达(2gR)~1/2时(又称第二宇宙速度),卫星以地球球心为焦点作抛物线运动,当然再也不可能返回地球,因为抛物线为非闭合曲线;当发射速度介于(gR)~1/2和(2gR)~1/2之间时,卫星作椭圆运动,并随发射速度的增大椭圆越扁,地球为椭圆的一个焦点,发射点为近地点.对于椭圆轨道,
Through the study of the knowledge of universal gravitation, we know that the minimum speed of launching a satellite is (gR) -1/2 (also known as the first cosmic velocity) when the satellite makes circular motion around the surface of the Earth at its maximum speed. When the launching velocity reaches ( 2gR) ~ 1/2 (also known as the second cosmic speed), the satellite parabolically moves the Earth’s center of the Earth as a parabola, and of course it is impossible to return to Earth anymore because the parabola is a non-closed curve; when the launch velocity is between (gR) ~ 1/2 and (2gR) ~ 1/2, the satellite makes an elliptical motion, and the ellipse is flattened with the increase of the launching velocity, the Earth is a focal point of the ellipse and the emission point is the perigee.For the elliptical orbit,