Deflecting APOPHIS with a Flotillaof Solar Sails

Jean-Yves Prado Olivier Boisard, Alain Perret,Guy Pignolet U3P France

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

■ The case of Apophis

■ Keyholes and resonant orbits

■ The Yarkovsky Effect

■ Mitigation mission

■ Comparison with other deflection techniques

Outlines

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

APOPHIS

Discovery

Discovered by:

Roy A. Tucker,David J. Tholen, Fabrizio Bernardi

Discovery date: June 19, 2004

Orbital characteristics

Aphelion distance: 1.099 AU

Perihelion distance: 0.746 AU

Orbital period: 323.6 d (0.89 year)

Inclination: 3.331°

Physical characteristics

Dimensions: ~250 m (estimated)

Mass:

Rotation period ~30h

2×1010 kg (estimated)

Mass of APOPHIS ~ 200 x @V=40,000 km/h

426 Days =>2036

417 Days =>2037

APOPHIS Fly by of the Earth on April 13, 2029

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

KEYHOLES

Orbit Uncertainty

+

-Earth

asteroid

+ Earth Gravity Assist

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

426.125 d

417.43 d

Possible Resonant Orbits

2037

2036

Resonant orbits up to 2130

0

20

40

60

80

100

120

140

417 419 421 423 425 427

APOPHIS Period (Days)

Ye

ar

of

retu

rn (

-20

00

)

1 s

Resonance Condition: Tap=m/n TEarth

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

KH distance distribution

XX = Year – 2K

‘safe area’

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

The Yarkovsky Effect

Ivan Osipovich Yarkovsky1844-1902

From PhD thesis Miroslav Broz, Charles University, Prague 2006

1987: Small variations in motion of LAGEOS explained using Yarkovsky theory

2003: First time measured on an asteroidGOLEVKA (Chesley)

based on 1991-1999 data

May 2003

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

The Diurnal Yarkovsky Effect

YE depends on: Distance to the Sun Asteroid size Asteroid shapeRotation axis obliquityRotation rateThermal 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

■ 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

Impact of the Yarkovsky Effect on the asteroid orbit

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

■ 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

Mission Design

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

■ High DV needed => Use of solar electric propulsion ■ Soyouz Fregat launch from Kourou assumed■ Typical mission profiles

Cruise

2011 option2016 option

2019 option

Departure date Dec. 14, 2011 Mar. 30, 2016 Dec. 5, 2019

Departure conditions v-inf = 3km/s, dec = -20.4deg v-inf=3.76 km/s, dec =-40 deg v-inf = 3km/s, dec = -18.4deg

Launch mass 1200kg 1200 kg 1200kg

Date of the Earth swing-by Apr. 18, 2013No Earth Swing-By

Apr. 11, 2021

Characteristics of the swing-by hp = 78000km, v-inf = 4.38km/s hp = 60000km, v-inf = 4.50km/s

Date of the rendezvous Mar. 5, 2014 Dec.22, 2018 Jan. 18, 2022

Total cruise duration 813 days (27 months) 997 days (33 months) 775 days (26 months)

Total Delta-V 1520m/s 1620 m/s 1350m/s

Xenon mass 95kg 100 kg 85kg

Final S/C dry mass 1105kg1100 kg

1115kg

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

2016 Departure

No Earth Swing By

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

2019 Departure

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

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

■ 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

■ 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

Conclusions

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

APOPHIS in the Egyptian mythology