Stable retrograde orbits around the triple system 2001 SN263

The near-Earth Asteroid 2001 SN263 is a triple system of asteroids and it is the target of the ASTER mission - First Brazilian Deep Space Mission. The announcement of this mission has motivated a study aimed to characterize regions of stability of the system. Araujo et al., characterized the stable regions around the components of the triple system for the planar and prograde cases. Through numerical integrations they found that the stable regions are in two tiny internal zones, one of them placed very close to Alpha and another close to Beta, and in the external region. For a space mission aimed to place the probe in the internal region of the system those results do not seem to be very interesting. Therefore, knowing that the retrograde orbits are expected to be more stable, here we present a complementary study. We now considered particles orbiting the components of the system, in the internal and external regions, with relative inclinations between 90 degrees < I <= 180 degrees, i.e. particles with retrograde orbits. Our goal is to characterize the stable regions of the system for retrograde orbits, and then detach a preferred region to place the space probe. For a space mission, the most interesting regions would be those that are unstable for the prograde cases, but stable for the retrograde cases. Such configuration provide a stable region to place the mission probe with a relative retrograde orbit, and, at the same time, guarantees a region free of debris since they are expected to have prograde orbits. We found that in fact the internal and external stable regions significantly increase when compared to the prograde case. For particles with e = 0 and I = 180 degrees, we found that nearly the whole region around Alpha and Beta remain stable. We then identified three internal regions and one external region that are very interesting to place the space probe. We present the stable regions found for the retrograde case and a discussion on those preferred regions. We also discuss the effects of resonances of the particles with Beta and Gamma, and the role of the Kozai mechanism in this scenario. These results help us understand and characterize the stability of the triple system 2001 SN263 when retrograde orbits are considered, and provide important parameters to the design of the ASTER mission.