  Recent studies of optimization methods and GNC of spacecraft near small
bodies focusing on descent, landing, rendezvous, etc., with key safety
constraints such as line-of-sight conic zones and soft landings have shown
promising results; this paper considers descent missions to an asteroid surface
with a constraint that consists of an onboard camera and asteroid surface
markers while using a stochastic convex MPC law. An undermodeled asteroid
gravity and spacecraft technology inspired measurement model is established to
develop the constraint. Then a computationally light stochastic Linear
Quadratic MPC strategy is presented to keep the spacecraft in satisfactory
field of view of the surface markers while trajectory tracking, employing
chance based constraints and up-to-date estimation uncertainty from navigation.
The estimation uncertainty giving rise to the tightened constraints is
particularly addressed. Results suggest robust tracking performance across a
variety of trajectories.
