Space Systems/loral, LLC

Ford Aerospace & Communications Corporation

Tung Y Liu

Scott W Tilley

John Scott Higham

Keith J Reckdahl

Kam K Chan

Fred N Chan

Yat Fai Leung

Carl T Plescia

Fatima Kazimi

Rhys Kevin Adsit

Mahabaleshwar K Bhat

Charles J Weyandt, Jr

Michel Bayloca

A spacecraft having a body, one or more appendages coupled thereto, and a controller that implements methods that rotate the one or more flexible appendages to point it (them) towards the Sun to reduce spacecraft attitude pointing disturbances and improves spacecraft attitude pointing. The steps of the one or more appendages are timed to deadbeat the disturbance imparted to the spacecraft body. Timing of the appendage steps may be such that the periodic disturbances are phased to substantially cancel each other, or phased to decrease the magnitude of the net disturbance. The present invention also cancels solar array slew disturbances. The present invention cancels predictable disturbance torques before they produce a pointing error, improving the spacecraft pointing performance. The present invention predicts a disturbance torque exerted on the body due to the controller moving the one or more appendages, calculates a feedforward torque necessary for the controller to cancel the disturbance torque and includes the feedforward torque in the calculation of the total control torque applied to the body.

Spacecraft and appendage stepping methods that improve spacecraft attitude pointing and cancel solar array slew disturbances

A spacecraft includes a plurality of thrusters mounted at predetermined locations on a spacecraft structure, individual ones the plurality of thrusters being fired for generating a torque about a desired axis. The firing of a thruster is partitioned into two firings that are offset in time by an amount .DELTA.t, wherein .DELTA.t=(1/2).times.(1/F).times.SF, where F is a dominant modal frequency, in Hertz, for any particular axis (nominally the 1st mode) of the spacecraft structure, and where SF is a scale factor that is adjustable about the frequency. In a presently preferred embodiment the thruster is a low thrust thruster that is mounted on a solar array panel, and the thrusters are fired in pairs.

Method using double thruster firings to deadbeat flexible solar array

Position control methods are described for satellites and spacecraft for controlling transition from thruster control to momentum wheel control in a three-axis stabilized spacecraft. Transition from a high-bandwidth, high-torque thruster-controlled stationkeeping (SK) mode to a low bandwidth, low torque momentum wheel On-Orbit Mode is carried out. Usually a unique threshold entry method to automatically initiate the transition mode at the point with the most favorable dynamics. Also, the disclosed method eliminates the use of nutation in conjunction with a deadbeat thruster sequence to correct the spacecraft attitude to improve pointing performance and significantly shorten the time spent in the transition mode.

Control system and method for spacecraft attitude control

A spacecraft (201) maintains its north-south positioning by using one of two pairs of single-gimballed throttled thrusters (221-224) on a face of the spacecraft (201). The throttles (118) and gimbals (116) of the thrusters (221-224) are controlled to produce torques on the spacecraft (201) that will maintain a desired attitude for the spacecraft (201) while simultaneously desaturating the momentum stabilizing wheels ( 120, 121 ) of the spacecraft (201).

Spacecraft attitude control and momentum unloading using gimballed and

An improved method for transitioning a spacecraft from a thruster (5) controlled, station keeping mode to an operational, on-orbit mode, in which attitude control is maintained using internal momentum wheels (3). The method first utilizes a thruster compensation technique to supplement the conventional transition mode control system. This compensation uses empirical thruster data to derate thruster (5) efficiency for extremely short pulse durations necessarily used in transition mode operation. Secondly, a three step deadbeat thruster (5) sequence is employed in which a first pulse linearizes spacecraft (1) motion prior to orienting and stopping nutation. This linearization provides improved accuracy in computing and shortens the waiting time for subsequent thruster (5) firings.

Compensated transition for spacecraft attitude control

Mechanical oscillations of a mechanism containing a stepper motor, such as a solar-array powered spacecraft, are reduced and minimized by the execution of step movements in pairs of steps, the period between steps being equal to one-half of the period of torsional oscillation of the mechanism. Each pair of steps is repeated at needed intervals to maintain desired continuous movement of the portion of elements to be moved, such as the solar array of a spacecraft. In order to account for uncertainty as well as slow change in the period of torsional oscillation, a command unit may be provided for varying the interval between steps in a pair.

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Union City, CA, United States of America

Tung Y Liu