  Near Rectilinear Halo Orbits (NRHOs), a subclass of halo orbits around the L1
and L2 Lagrange points, are promising candidates for future lunar gateways in
cis-lunar space and as staging orbits for lunar missions. Closed-loop control
is beneficial to compensate orbital perturbations and potential instabilities
while maintaining spacecraft on NRHOs and performing relative motion maneuvers.
This paper investigates the use of nonlinear model predictive control (NMPC)
coupled with low-thrust actuators for station-keeping on NRHOs. It is
demonstrated through numerical simulations that NMPC is able to stabilize a
spacecraft to a reference orbit and handle control constraints. Further, it is
shown that the computational burden of NMPC can be managed using specialized
optimization routines and suboptimal approaches without jeopardizing
closed-loop performance.
