Spacecraft spin axis capture system and method
AssigneeHughes Aircraft Company
InventorJohn W. Smay
Life of this patent
Estimating the term…
Abstract
A control system and method for causing a spacecraft (10) initially spinning about a principal axis of inertia (H) to transition to spin about an arbitrary command axis (3) is presented in which the capture maneuver is performed in a way to preserve spacecraft attitude knowledge without sensor or attitude propagation by using a simple rate feedback loop. The capture is accomplished by applying a step torque about axes (1) and (2) transverse to the desired spin axis (3) creating an initial nutation. The nutation is subsequently damped actively by closing a rate feedback loop with a low pass filter and applying transverse torques proportional to the transverse nutational rate.
Claims14
In a spacecraft having a body spinning in a steady state about a principal axis of inertia and having an angular momentum vector, and said spacecraft having a control system, a method of transitioning the spacecraft body to spin about an arbitrary commanded axis having two mutually perpendicular transverse axes, said commanded spin axis coning about said angular momentum vector in said steady state, said method comprising the steps of:
- applying predetermined torques T.sub.1 and T.sub.2 about each of said transverse axes to cancel wobble of said commanded spin axis and thereby inducing nutation about said transverse axes;
- measuring rates of nutation about said transverse axes;
- and
- applying nutation damping torques about said transverse axes proportional to said transverse nutation rates to actively dampen said nutation and drive said commanded spin axis to the position of the initial momentum vector.
In a spacecraft spinning in a steady state about a principal axis of inertia and having an angular momentum vector, said spacecraft having a control system and a thruster for use in elevating said spacecraft to a desired orbit, said thruster having thrust axis which is angularly displaced from said principal axis of inertia and thereby coning about said angular momentum vector in said steady state, a method of transitioning to spin about said thrust axis comprising the steps of:
- applying predetermined torques T.sub.1 and T.sub.2 about a pair of transverse axes normal to said thrust axis to cancel wobble of said thrust axis and thereby inducing nutation about said transverse axes;
- measuring rates of nutation of said spacecraft about said transverse axes;
- and
- applying nutation damping torques about said transverse axes proportional to said transverse nutation rates to dampen said nutation and drive said thrust axis to the initial position of said momentum vector.
A control system in a spacecraft spinning in a steady state about a principal inertia axis and having an angular momentum vector for transitioning the spacecraft to spin about an arbitrary commanded axis with first and second mutually perpendicular transverse axes, said commanded spin axis coning about said momentum vector in said steady state comprising:
- measuring means for detecting angular rates of motion about each of said transverse axes;
- thruster means for providing positive and negative torques about said first and second transverse axes;
- and
- control means for firing said thruster means to produce a transverse torque inducing a nutation rate about said transverse axes and for subsequently firing said thruster means to produce a wobble canceling torque about said first and second transverse axes proportional to the transverse nutation rate and having a rate feedback loop with a low pass filter having a gain G(0) over a frequency range from zero to the spacecraft body nutation frequency to dampen said nutation and drive said commanded spin axis to the initial position of said momentum vector.
Dependencies are inferred from the claim text.