The concept and operating characteristics of a radially vibrating, gravitational gradient sensor are presented. The sensor is a tuned mechanical oscillator that responds to gravitygradient forces when it is rotated in a stationary gravitational field. Because of the inherent dynamic magnification resulting from resonant or near-resonant operation of the sensor it obtains high sensitivity and can potentially be used as an accurate attitude control sensor, an orbital altimeter, or a navigation aid in a variety of satellite applications.
Nomenclature
A= nondimensional amplitude C = sensor disk or tube polar inertia AT" = C/mro* = sensor inertia parameter /o = instantaneous inertia of sensor Q r -generalized dissipative force c = viscous damping coefficient k = sensor spring constant I = free length of spring n = damping factor -\ r = n + r 2 = sensor axial coordinate I = time u -test mass displacement from equilibrium x = r/ro = 1 + u/r 0 = 1 + y y = M/r 0 z =' y -o>o 2 /2o>n 2 c c -critical viscous damping coefficient Wo = sensor and satellite mass mi = sensor test mass r 0 = equilibrium length of spring at 0 = ft = constant r lt r 2 = distances as defined in Fig. 1 m = ra 0 Wi/(7??o + mi) = reduced system mass A A = 12 -w 0 $ = phase angle 12 = predominant (constant) absolute angular velocity of the sensor f = c/c c , damping ratio /u = earth's gravitational constant i f / = oscillatory angular displacement about an average value of 0' PL -distances as defined in Fig. 1; i = 1,2 co 0 = orbital angular velocity ton = sensor natural frequency in a gravitational field co r .-sensor natural frequency at rest (0 = 0) ov = undamped natural frequency of the sensor 0,0 ~ sensor absolute angular displacement and rate, respectively 0', 0' = sensor angular displacement and rate, respectively, relative to local vertical 0'av = ft -o>o = average value of angular velocity relative to the local vertical