This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

25 April 2011

Paper: Deflecting APOPHIS with a flotilla of solar shields

Deflecting APOPHIS with a flotilla of solar shields

Jean-Yves Prado (a), , , , Alain Perret (b), and Olivier Boisard (b),
a CNES, Toulouse 31401, 18 Avenue Edouard Belin, Toulouse cedex 9, France
b Union pour la Promotion de la Propulsion Photonique, 37530 Nazelles-NĂ©gron, France

The possibility to use the photonic pressure from the Sun for acting upon the orbit of a man-made object is well known. What is presented in this paper is the capacity to use a solar sail like vehicle to change the orbit of a small body of the solar system by hovering over its sunlit surface. One of the forces that affect the orbit of small bodies is a tiny but permanent thrust of thermal origin, the intensity and direction of which are directly related to the nature of the soil, the characteristics of the rotation and the physical properties of the body. This effect is known as the Yarkovsky Effect. It concerns mainly hundred meter class asteroids. There are hundred thousands of small bodies of this type. About 10% of them are classified as Near Earth Object and one of them, APOPHIS, is of special interest. APOPHIS has been discovered in 2004. Its diameter is estimated to be 270 m. Its rotation period is around 30 h so the Yarkovsky Effect on its orbit should not be negligible. These parameters and possibly others should be refined in 2012 when this asteroid can be observed again. APOPHIS will make a very close (40,000 km) approach to the Earth in April 2029. Depending on the geometry of its swing-by, it can be placed on an impact orbit to the Earth and present a danger for the future decades. The areas that correspond to such trajectories are called Resonant Orbit Keyholes and are only a few hundred meter wide. From the observation in 2012, it will be possible to determine the magnitude of the Yarkovsky Effect on APOPHIS and to greatly improve the prevision of its 2029 swing-by. If the Yarkovsky Effect is found to be important, cancelling it will be sufficient to avoid any keyhole and prevent any future collision with the Earth. We call Yarkovsky Effect Suppression (YES) this deflection method. This effect can be cancelled by shadowing and cooling down the asteroid with a flotilla of solar shields. This new type of solar sails will have to counter the photonic pressure in order to maintain their hovering position. In this paper, we propose a preliminary mission design and the main system requirements, especially as regards station keeping. This mission is named SHADOW. Finally we discuss the pros and cons of this strategy and compare its effectiveness to already identified mitigation methods.

Link: ScienceDirect (Advances in Space Research)
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