International Journal of Space Science and Engineering
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International Journal of Space Science and Engineering (2 papers in press)
LEO Satellite Formation Flying via Differential Atmospheric Drag by Andrew Tang, Xiaofeng Wu Abstract: Formation flying involves multiple spacecraft flying with pre-defined relation to each other. This allows a number of individual, smaller satellites to work together and accomplish tasks extraneous to single satellite systems. However, the required precision of orbital positioning and control makes the maintenance of such formations quite challenging. This is particularly true for space systems without propulsive controls; even for systems equipped with active control, propellant consumption can be quite high.
To facilitate orbital control, this study investigates formation flying in low earth orbit (LEO), focusing primarily on propulsion-free methods of control for micro and nano- class satellites such as aerodynamic differential drag. A fuzzy logic control algorithm was developed to control the satellites position by manipulating the drag configuration of each satellite in the formation. The outcome of this study shows that successful formation control can be achieved using drag forces alone. The time taken for each formation control and by-products, including altitude loss are evaluated. The orbital modelling presented here can be used as the baseline for a control algorithm developed for station keeping of satellites in low earth orbit. Keywords: formation flying; satellite orbit; atmospheric drag; low earth orbit; LEO; Cube Satellite; leader-follower formation.
Optimal Trajectory Design and Analysis for Soft Landing on the Moon from Lunar Parking Orbits by Santosh Kumar Choudhary, Kaushik Raj, Venkatesan Muthukumar Abstract: This article studies the optimal control solution of the moon-lander problem. The main purpose of this article is to investigate the optimal strategy for trajectory design to ensure the soft landing of the lander from the Lunar parking orbit to the lunar surface with minimum consumption of fuel.
The trajectory design of lunar lander is studied via two cases by formulating the optimal control problems, where specific requirements of this soft landing problem are all incorporated in the problem formulation.
To analyze the proposed optimal strategies for a soft landing the paper briefly illustrates the numerical simulation results and it shows that the required velocity for the soft landing is achieved with minimum fuel consumption.
The investigated computational methods for the optimal solutions of the moon-lander problem in both two cases are conceptually simple and efficient. Keywords: Moon-lander; Optimal control; Lunar parking orbit; Soft landing; Pontryagin’s Principle; Two-point boundary value problem; Bound constrained optimization technique.