The Navigation Campaign of the NASA OSIRIS-REx mission consists of three phases: the Approach phase, Preliminary Survey phase, and the Orbital A phase. These phases spanned from August 2018 until February 28, 2019. The OSIRIS-REx spacecraft arrived at asteroid (101955) Bennu on December 3rd, 2018 thereby initiating the Preliminary Survey phase consisting of five 7-km altitude flybys of the asteroid. Orbit insertion followed on December 31st, 2018 commencing the Orbital A phase whereby the spacecraft’s average frozen orbit radius was less than 2 km. In this paper the small forces are presented that govern the spacecraft dynamics near the asteroid for the Navigation Campaign. These small forces include: solar radiation pressure, spacecraft thermal re-radiation, the antenna and LIDAR radiation pressure, and trending from desaturation maneuvers (desats). Extensive work on modeling these forces has enabled the navigation performance to exceed expectations and has reduced the stochastic accelerations below 1 x 10–12 km/s2 resulting in smaller trajectory predicted errors, essential for science planning of the mission.