The third project topic was disk mass potential. This topic was designed to make measurements of the distances to disk stars as well as their proper motions. The results of the third topic of study were to be combined with the results of the fundamental galactic parameters portion of the study to determine the Solar System's position and velocity in the galaxy. The final topic dealt with dark matter distribution in the Milky Way. SIM data was to be used to create a three-dimensional model of mass distribution in the Galaxy, out to a radius of 270 kiloparsecs (kps). Astronomers were to then use two different tests to determine the galactic potential at large radii.