Gravitational orbit-attitude coupling for very large spacecraft

Motion equations for the gravitationally coupled orbit-attitude motion of a spacecraft are presented. The gravitational force and torque are expanded in a Taylor series in the small ratio (spacecraft size/orbital radius). A recursive definition for higher moments of inertia is introduced which permits terms up tofourth order to be retained. The expressions are fully nonlinear in the attitude variables. A quasi-sunpointing (QSP) passive attitude-control mode is used to assess the effects of higher moments of inertia and gravitational coupling. The attitude motion is detectably coupled to the orbital motion. However, the higher moments of inertia influence only the attitude motion.Nomenclature f _G ,g _G ,f _Gi ,g _Gi total gravitational force and torque and their components of orderi in =/r ₀ - angular momentum of spacecraft about 0 and the spacecraft mass center - J ⁱ ,I ⁱ general moment of inertia about 0 and the spacecraft mass center - second (dyadic), third (triadic), and fourth (tetradic) moment of inertia about 0 and the spacecraft mass center - A andB (and related components) of the second, third and fourth moments of inertia about 0, see Equation (9) - M, m Earth's mass, spacecraft mass - Q ^ba rotation matrix taking _a into _b - position vector from attracting body's mass center to a general mass element, to 0 and to the spacecraft mass center - ₁, ₂, ₃ basis vectors of reference frame - , , _N misalignment angle betweenb ₃ and the (projected) true position of the Sun, its oscillatory component and nominal value - unit dyadic (-identity matrix) - ratio of characteristic spacecraft dimension to orbital radius - pitch angle (aboutb ₂ axis) - Earth's gravitational parameter - , position vector from 0 to a general mass element and the spacecraft mass center - , the (projected) true longitude of the Sun and the true longitude of the spacecraft - _/ angular velocity of reference frame with respect to - (·), (^*), (^o) d()/dt with respect to inertial space _I , and orbiting frame _O and a body-fixed spacecraft frame _b Presented at AAS/AIAA Astrodynamics Conference, Aug. 9–11, 1982.