Three-dimensional LEO keeping using low-thrust

Abstract

The purpose of this paper is to investigate the two methods for low Earth orbit keeping: periodic low-thrust (PLT) method and continuous low-thrust (CLT) method. The perturbation forces which can cause deviation of the low Earth orbit and are considered include the centrifugal force and Coriolis force due to the Earth's rotation, the odd and even harmonics of the gravitational field, and the aerodynamic drag. The allowable value in the altitude drop is −5 km. In the PLT method, the thrust is turned on periodically when the altitude drop reaches the allowable value. Then it is turned off when the deviation is corrected to zero and another cycle of orbit keeping starts. In the CLT method, the thrust vector is set to compensate the vector sum of the perturbation forces so that the satellite remains in its initial circular orbit all the time. It is found that if the altitude of the initial circular orbit is 128 km, the two methods have the same fuel consumption. Below 128 km the CLT method must be used, and above 128 km the PLT method is much more economic. The same numerical computation has been performed when the allowable value in altitude drop is −10 km. We find the same characteristics. The change from CLT method to PLT method should occur at 135 km.