July 29, 2014 -
we are not in direct sunlight (such as during launch and sampling). The guidance system includes many components including star trackers, sun sensors, a laser range-finder, and on-board image processing capabilities.
I describe the journey to Bennu, including details on the speeds involved in my blog post How to Get to Bennu and Back. We will leave Earth with a hyperbolic escape velocity of 5.4 km/s (over 12,000 mph) on an Atlas V rocket. We will sneak up on Bennu with a relative approach velocity of 20 cm/s (~0.45 mph). When we return to Earth the sample return capsule will hit the top of the atmosphere with a speed of 12.4 km/s (27,738 mph).