Autonomous proximity operations to explore small solar system bodies (asteroids and comets), servicing of aerospace vehicles, and active space debris removal, are likely to increase in the future with NASA's Asteroid Redirect Mission and Grand Challenge, and planned activities in autonomous rendezvous/proximity operations (ARPO) and active debris removal. Autonomous navigation is essential for these applications. The concept proposed here is to have a single stable estimator for the naturally coupled translational and rotational motion of an observed object from only vision-based, infra-red or lidar measurements, without needing a dynamics model for this object, during proximity operations. This estimator can also be used to improve an existing dynamics model. This avoids the need for measurements from external sources, like GPS, which is anyway not available for proximity operations near asteroids or comets. It also avoids mishaps due to changes in sensors and estimation schemes used during close proximity operations between spacecraft, as witnessed during the DART and Orbital Express missions. Attitude and translational motion of spacecraft, asteroids and comets are dynamically coupled through natural effects like gravity as well as control forces and torques for spacecraft. This coupling can also be used to estimate the mass and gravity parameters of the asteroid/comet.