Deflecting APOPHIS with a Flotilla of Solar Sails

1. Deflecting APOPHIS with a Flotillaof Solar Sails Jean-Yves Prado Olivier Boisard, Alain Perret,Guy Pignolet U3P France

2. Outlines • The case of Apophis • Keyholes and resonant orbits • The Yarkovsky Effect • Mitigation mission • Comparison with other deflection techniques ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

3. APOPHIS Mass of APOPHIS ~ 200 x@V=40,000 km/h ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

4. APOPHIS Fly by of the Earth on April 13, 2029 417 Days =>2037 426 Days =>2036

5. Orbit Uncertainty + - KEYHOLES + Earth Gravity Assist asteroid Earth ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

6. 1 s Possible Resonant Orbits 2037 417.43 d 2036 426.125 d Resonance Condition: Tap=m/n TEarth ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

7. KH distance distribution ‘safe area’ XX = Year – 2K ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

8. The Yarkovsky Effect 1987: Small variations in motion of LAGEOS explained using Yarkovsky theory 2003: First time measured on an asteroid GOLEVKA (Chesley) May 2003 Ivan Osipovich Yarkovsky 1844-1902 based on 1991-1999 data From PhD thesis Miroslav Broz, Charles University, Prague 2006 ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

9. The Diurnal Yarkovsky Effect • YE depends on: • Distance to the Sun • Asteroid size • Asteroid shape • Rotation axis obliquity • Rotation rate • Thermal properties: • surface conductivity • thermal inertia • Very sensitive for the 1 m / 10 km class of Asteroids • Seasonal effect can be neglected for >100m asteroids ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

10. Impact of the Yarkovsky Effect on the asteroid orbit • Tiny effect (10-10 / 10-13m/s2) but permanent • Main effect on semimajor axis • Order of magnitude for da/dt variation of tens to hundreds meters per year • Position error varies with t2 • Example: with da/dt =10m/year position shifts 100m in 1 year, 400 m in 2 years… 100m 1km 4 km • Can be positive (outward spiral) or negative (inward spiral) depending on obliquity • Determination of its direction and magnitude for propagating orbit parameters with an accuracy coherent with keyhole sizes • General question, not specific to APOPHIS ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

11. Mission Design • A Transfer Module using SEP carries 4 x 200 kg solar sails to be deployed near APOPHIS • Formation Flying mode of the sails controlled by the TM • The sails hover a few km over the asteroid • They can shadow only the surface which is the most effective w.r.t. YE • No direct link from the Earth to individual sails • Chemical propulsion needed for balancing the photonic pressure (DV ~1.1 m/s/day) • Photonic pressure could be decreased by using a mesh instead of a film screen • 2 sets of TM+SS required (so 2 launches) can be required for efficiency and reliability ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

12. Cruise • High DV needed => Use of solar electric propulsion • Soyouz Fregat launch from Kourou assumed • Typical mission profiles ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

13. 2016 Departure No Earth Swing By ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

14. 2019 Departure ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

15. Image Credit Olivier Boisard ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

16. 2 categories: Impulsive/Slow Push Techniques Impulsive techniques can be seen as a preliminar to send weapons in space Slow Push Techniques (from NASA report to US Congress): Focused Solar Boil off material using large mirror Low TRL, complex Pulsed Laser Boil off material with a laser Low TRL Mass Driver Needs to land, Asteroid characteristics dependant Low TRL Gravity Tractor Efficiency in D-5, High TRL Asteroid Tug Needs to land, Asteroid characteristics dependant Low TRL Enhanced YE Heavy, Asteroid characteristics dependant Low TRL YES Efficiency in ~D-1, High TRL but applicable only if YE is present Comparison with Other Deflection Techniques ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

17. Conclusions • Cancelling YE can be an efficient and reliable method for deflecting a NEO < km • Effort in such technology would benefit several types of missions • Canceling YE for a given period of time, even if not needed for APOPHIS, would validate the feasibility of the method • The required technology is very similar to the one required for solar sailing • International coordination required ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22

18. APOPHIS in the Egyptian mythology ISSS 2010 Deflecting Apophis with a flotilla of solar sails New York July 20-22