Small Elliptic Orbit Design For Groundemergency Observation And Research On Method Of Orbit Maneuver

As space information system offers strong support to military activities and rescue missions now, satellite technology has played an indispensable role in quick response to emergencies. However, how to reduce cost and improve response ability, is one of the focuses of the technology of operationally responsive space. With that as the background, this thesis performs the research on the technologies of small elliptic orbit design for ground emergency observation and the research on analytical algorithm as well as optimization algorithm for ground track manipulation under J2 item perturbation within a limited time. The main contents as follows:Firstly, since only a few days of precise observations are needed for emergency relief tasks, the design scheme of the small elliptic orbit in which a satellite make Earth observation near the perigee just for a short time is presented and the design method is deduced. Consideration is given both to reduce atmospheric damping and to improve the resolution of ground objects in the scheme compared to that of a low circle orbit. A small elliptic repeating orbit is designed due to the requirement of revisit rate. Focusing on ground resolution constraints of elliptical orbit, a link between ground resolution and perigee is established. Then the criteria of ground observation is deduced with the help of the rule of apsidal motion, and so is the design method of controls parameter. This thesis summarizes the calculating method of illumination intensity for arbitrary point on the ground, and the calculating methods of two critical moment of the specified illumination intensity of the same day is deduced in turn, for that the instant light intensity can’t be determined by local time of descending node.Secondly, after building the model of satellite ground trace, an algorithm for control parameters of orbit maneuver optimization is designed, the results of which precisely adjust ground track. As it is of low computing efficiency for searching point by point, a model of terminal cruising phase is established considering the theory of mean orbit, and furthermore, a modified numerical algorithm under single pulse is designed, which offers higher computation speed. According to the characteristics of multiple local minimum points in the optimization model under multiple-pulse, a bi-level algorithm based on genetic algorithm and nonlinear programming algorithm is designed, which conquers the prematurity problem of genetic algorithm, and which greatly increased the computation efficiency and stability. Results of the algorithm which involve the outcome of four-pulse, make it clear that a single-impulse with a coasting-flight phase is the optimal impulse. For the case whose target orbit is given, the characteristics of the feasible region is analyzed, and it turns out that genetic algorithm can effectively solve the optimization model. Results of algorithm verifies that if target orbit is a circle orbit, the solution need two pulse at least, and if target orbit is an elliptical orbit, the solution need three pulse at least.Finally, three kinds of analytical algorithm for ground track manipulation are deduced. It first gives the impulse thrust model of small elliptical orbit, and introduces modified equinoctial elements. Based on the model of cruising phase, four main impact factors of ground track are analyzed, and then the relationship between these factors and the impulse thrust model is established. Simplified formula of the difference between mean anomaly of the first track at the target latitude and the initial one is derived. Then three kinds of analytical algorithm are deduced: the one based on perturbation model with reference satellite whose terminal longitude difference between non-maneuvering ground track and the target is already known; the one based on perturbation model without reference satellite whose initial longitude difference between the orbit and the target is already known; the one based on two-body model with reference satellite whose terminal longitude difference between non-maneuvering ground track and the target is already known. Analytical solutions of all analytical algorithms turn out to be cubic equations. By adjusting the coefficients of these equations, the optimal pulse and all feasible solution can be calculated. Algorithms are all tested in two situations which means the initial orbit is either a circle orbit or an elliptical orbit. The results shows that all the three methods are of high precision and high computation speed, they can be used in different situation according to different initial conditions.