The SHADOW Mission:
Deflecting APOPHIS with a flotilla of solar shields
Prado, Jean-Yves1; Perret, A2; Boisard, O2; Bertrand, R1
1CNES; 2U3P
The orbit of asteroids similar to Apophis is difficult to extrapolate over the long term, mainly due to the uncertainties surrounding the effect of non-gravitational forces. The Yarkovsky Effect (YE), which is the main unknown, refers to a minute but permanent thrust, 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 asteroid.
The SHADOW programme we are proposing would be staged in the following way:
- As soon as possible, send a probe to rendezvous with Apophis and gather the requested information to assess the YE. From this input, determine the geometry of its Earth fly-by in April 2029 to establish to within a kilometre the location of the ‘key holes’ that, if passed through, would lead to an Apophis-Earth impact in a near future,
- Depending on the position of the "key holes" with respect to the uncertainty volume of the 2029 fly-by, a decision can be made to deflect Apophisand, consequently, to design the mission to be undertaken,
- If the YE is found to be important, cancelling it will be enough to avoid any key hole and prevent any collision with the Earth. This can be achieved by shadowing and cooling down the asteroid with a flotilla of solar shields. These sorts of solar sails will have to counter the photonic pressure in order to maintain their hovering position.
In this paper, using observations made on 6489 Golevka, we show that the YE can alter the orbit of Apophis by up to several thousand kilometres within a decade and we suggest a preliminary mission design for the observational part.
As for the YE cancelling stage, we address the main system requirements, especially as regards station keeping. Finally we discuss the pros and cons of the YES (Yarkovsky Effect Shadowing) strategy and compare its effectiveness to other already proposed mitigation methods.