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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 39853 (08)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Zohoor, Hassan; Sayyadi, Hassan
- Abstract:
- The collision of moderately large asteroids and comets also referred to as Near-Earth Objects (NEO's) with earth would have catastrophic consequences. Such events have occurred in the past and may occur again in the future. However, for the first time in known history, humanity may have the technology required to counter this threat. Methods studied for mitigation of this hazard are based on deflecting asteroid's trajectory and are normally divided into two basic categories: high energy impulsive methods, and long-duration low-thrust methods. Two parts of mission to be optimized are the trajectory of spacecraft to reach the target and the deflection strategy which could be analyzed by the theory of optimal control. Three common deflection strategies were studied in this research, Kinetic Impactor, Nuclear Detonation and Gravity Tractor. The kinetic energy impactor deflection method relies upon an impactor vehicle launched onto an interplanetary intercept trajectory. In nuclear detonation strategy, the neutron radiation generated by the explosion penetrates a small depth into the NEO surface, superheating a thin shell of material that then blows off. This blow-off of superheated mass imparts an impulsive thrust to the NEO. The Gravity Tractor (GT) is a fully controlled asteroid deflection concept using the mutual gravity between a robotic spacecraft and an asteroid to slowly accelerate the asteroid in the direction of the hovering spacecraft. Appropriate performance measure is presented for these three methods. The asteroid deflection formula used in definition of performance measure in mission optimization was also corrected. A hybrid method of optimization was established using Pontryagin's maximum principle and the method of variation of extremals, which led to a nonlinear programming (NLP) problem. As a special case of kinetic impactor, the trajectory of impactor vehicle intercepting Apophis was optimized. Optimal deflection strategies were also found for nuclear detonation and gravity tractor methods.
- Keywords:
- Optimal Control ; Near-Earth Asteroid ; Celestial Dynamics ; Asteroid Deflection ; Low-Thrust Propulsion
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