[Previous] | [Session 4] | [Next]
M.A. Murison (U.S. Naval Observatory)
The scanning pattern of observations from a spin-stabilized, precessing astrometric spacecraft constrains the mission astrometric errors through the geometry that determines two distributions on the sky: the distribution of observation density and the distribution of scan angle (the angle of scan direction with respect to an ecliptic meridian through a given location). In this paper, the geometry underlying the distributions is presented. Then, assuming a given single-measurement error, simulated astrometric observations are accumulated on an equal-area grid on the sky. The behaviors of the astrometric error distributions are investigated as functions of the geometry control parameters: spin period, precession period, and precession cone angle (nominal angle between spin axis and Sun direction). Optimal values are determined for the specific case of the NASA MIDEX mission, FAME.