  The goal of the OSIRIS-REx mission is to return a sample of asteroid material
from Near-Earth Asteroid (101955) Bennu. The role of the navigation and flight
dynamics team is critical for the spacecraft to execute a precisely planned
sampling maneuver over a specifically-selected landing site. In particular, the
orientation of Bennu needs to be recovered with good accuracy during orbital
operations to contribute as small an error as possible to the landing error
budget. Although Bennu is well characterized from Earth-based radar
observations, its orientation dynamics are not sufficiently known to exclude
the presence of a small wobble. To better understand this contingency and
evaluate how well the orientation can be recovered in the presence of a large
1$^{\circ}$ wobble, we conduct a comprehensive simulation with the NASA GSFC
GEODYN orbit determination and geodetic parameter estimation software. We
describe the dynamic orientation modeling implemented in GEODYN in support of
OSIRIS-REx operations, and show how both altimetry and imagery data can be used
as either undifferenced (landmark, direct altimetry) or differenced (image
crossover, altimetry crossover) measurements. We find that these two different
types of data contribute differently to the recovery of instrument pointing or
planetary orientation. When upweighted, the absolute measurements help reduce
the geolocation errors, despite poorer astrometric (inertial) performance. We
find that with no wobble present, all the geolocation requirements are met.
While the presence of a large wobble is detrimental, the recovery is still
reliable thanks to the combined use of altimetry and imagery data.
