Abstract
On the conditions that the spacecraft engine is in finite thrust mode and the maneuver time is given, it takes a long time to compute the minimum duration transfer trajectories of space-to-ground vehicles, which is mainly because the initial values of the adjoint variables involved in the optimization model have no definite physical meanings and the model is sensitive to them. In order to develop space-to-ground transfer trajectory programmes in real time in an uncertain environment for the decision makers, we propose a fast method for computing the minimum duration transfer trajectories of space-to-ground vehicles with the given position of the landing point and the arbitrary maneuver point. First, the optimization model based on the hybrid method is established to compute the minimum duration transfer trajectory. Then, the region composed of maneuverable points is gridded and the initial values of the adjoint variables and the values of partial state variables of the minimum duration transfer trajectories at all gridded points are computed and saved to a database. Finally, the predicted values of the initial values of the adjoint variables and the values of partial state variables at any maneuver point within the region composed of maneuverable points are computed by using a binary cubic interpolation method. Finally, the minimum duration transfer trajectory is obtained by the hybrid method which takes the neighborhood of the predicted values as the search ranges of the initial values of the adjoint variables and the values of partial state variables. Simulation results demonstrate that the proposed method, which requires only 2.93% of the computational time of the hybrid method, can improve substantially the computational time of the minimum duration transfer trajectory of a space-to-ground vehicle under the guarantee of ensuring accuracy. The methodology of converting the time domain into the space domain is well applied in this paper.
Highlights
The transfer trajectories of spacecraft, such as return satellites, manned spacecraft, space shuttles, space-to-ground kinetic weapons, and other kinds of space-to-ground vehicles, from their orbit to the landing point is uniformly referred to as space-to-ground transfer trajectories
According to the research status, we propose a fast method based on the interpolation scheme and the hybrid method for computing the minimum duration transfer trajectories
The predicted values of the initial values of the adjoint variables and the values of partial state variable at any one maneuver point in the region composed of maneuverable points are computed by using a binary cubic interpolation method [29, 30], and the minimum duration transfer trajectory is computed by the hybrid method which takes neighborhood of predicted values as the search ranges of the initial values of the adjoint variables and the values of partial state variables
Summary
The transfer trajectories of spacecraft, such as return satellites, manned spacecraft, space shuttles, space-to-ground kinetic weapons, and other kinds of space-to-ground vehicles, from their orbit to the landing point is uniformly referred to as space-to-ground transfer trajectories. The space-to-ground transfer trajectories are studied by hybrid methods [20–22]. Computing a minimum duration transfer trajectory based on the hybrid method can obtain an accurate solution, but still takes a relatively long time. According to the research status, we propose a fast method based on the interpolation scheme and the hybrid method for computing the minimum duration transfer trajectories. We study a typical space-to-ground transfer trajectory which only takes into consideration of the energy but not the heat rate, normal load, and dynamic pressure. The typical space-to-ground transfer trajectory adopts the zero angle of attack and ballistic reentry mode (Figure 1). The main content is as follows: First, we establish the optimization model for the minimum duration transfer trajectory by using hybrid method. We propose the fast method for computing the minimum duration transfer trajectory. We carry on the simulations and the result analysis to demonstrate the high computational efficiency of the proposed method
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