Fred C ChanLos Banos, CA

4537375, Aug 27, 1985

Apr 21, 1983

6/487364

Fred N. Chan - Atherton CA

Ford Aerospace & Communications Corporation - Detroit MI

B64G 126

244171

Transients and steady state error induced in maneuvering a satellite due to a disturbance torque caused by thrust mismatch or differential in the alignment of thrusters with respect to the center of mass are minimized by introducing a torque balancing bias at the input of a thrust modulator of the thrusters prior to sensing position or attitude error. The bias may instantly off-modulate the thruster control signal to cancel the effects of attitude transients before errors develop. Other axes thrusters may be on-modulated instantaneously to compensate for cross-axis torque. The bias may be introduced into the satellite control scheme by manual ground control or in automatic on-board compensation based on stored parameters obtained for example from calibration measurements. Specifically, the torque balancing bias may be developed by reference to thrust mismatch detected and stored during previous maneuvers, thus anticipating expected attitude error without actual detection thereof.

4829301, May 9, 1989

Nov 13, 1987

7/120556

Fred N. Chan - Atherton CA
Gerald J. Wensley - Sunnyvale CA

Ford Aerospace & Communications Corporation - Detroit MI

H03L 706
H03M 100

341122

There is provided a digitally controlled first order hold circuit and waveform synthesizer for digitally controlling the representation of a function over an approximation interval. In accordance with the operation of the invention, the first order hold circuit and waveform generator receives a digital data input signal which contains initial condition data, up/down data, and slope data for the approximation interval. The initial condition data is loaded into an up/down counter which is incremented using counting data at a rate depending on the value of the slope data and in a direction depending on the value of the up-down data. In order to minimize delays arising from data acquistion, two frequency synthesizer circuits are provided such that one frequency synthesizer provides counting data while the other frequency synthesizer receives slope data. During alternating intervals, the other frequency synthesizer circuit provides counting data while the other circuit receives slope data. In addition, long length data input signals covering a plurality of approximation intervals are provided to reduce the demands on a main system central processing unit.

4591118, May 27, 1986

Feb 17, 1984

6/619169

Fred N. Chan - Atherton CA

Ford Aerospace & Communications Corporation - Detroit MI

B64G 136

244171

Apparatus for enhancing the stability of a spacecraft (2) about a sensing axis (4). The spacecraft (2) may be of the three axis stabilized or spin stabilized variety. An attitude sensor (3) determines the offset angle (A) formed between a face (8) of the spacecraft (2) and an astronomical body (6), such as the earth. The sensor (3) produces an attitude signal (14) which is processed by compensation electronics (21) and fed to a torquing means (25) to close the angle (A) to within a desired preselected deadband (24). The attitude signal (14) is hysteresis conditioned to (1) suppress saturated portions (18, 20) of the signal (14) having opposite polarity with respect to spacecraft (2) angular velocity, to avoid unwanted spacecraft (2) spinup; (2) allow passage to the compensation electronics (21) of saturated portions (18, 20) of the signal (14) having the same polarity with respect to the angular velocity of the spacecraft (2), to damp the spacecraft (2) velocity; and (3) suppress the signal (14) when the sensor (3) is not detecting the body (6), in order to limit the velocity of the spacecraft (2).

4767084, Aug 30, 1988

Sep 18, 1986

6/908757

Fred N. Chan - Atherton CA
Wallace E. Reimche - Saratoga CA

Ford Aerospace & Communications Corporation - Detroit MI

B64G 124

244164

Apparatus for autonomously performing stationkeeping maneuvers for three-axis stabilized spacecraft (1) such as geosynchronous satellites. For each of one or more spacecraft axes (y, z) the invention autonomously performs desaturation of a momentum/reaction wheel (31-32, 41, respectively) associated with that axis, while simultaneously accomplishing the preselected compensation of the spacecraft's east-west position. Thrusters (35-38, 45-48) having a polarity corresponding to the desired desaturation polarity are fired in a particular sequence: when a preselected east-west firing bias is present, the thrusters fired are solely from that face of the spacecraft (1) needed to counteract the east-west deviation. After the bias has been worked down, thrusters are fired from alternating spacecraft faces. An open loop portion (63-74) of the instant circuit performs or completes working-down of the east-west firing bias once per preselected firing period in those cases where the desaturation maneuvers are not sufficient to perform this function by themselves.

4599697, Jul 8, 1986

Aug 11, 1982

6/407196

Fred N. Chan - Atherton CA
Frank C. Nilsen - Mountain View CA

Ford Aerospace & Communications Corporation - Detroit MI

B64G 126

364434

A digital system for controlling the attitude of a spacecraft (14), e. g. , a satellite, with respect to three orthogonal axes. The system can control satellites (14) in parking orbit, transfer orbit, or final operational orbit, whether or not the satellite (14) employs one or more momentum wheels. A processor (2) converts weighted data from spacecraft sensors (12), representing angular orientation and angular velocities about each of the three axes, into thruster pulsetrain signatures to command the firing of each of six thrusters positioned about spacecraft (14), a positive and a negative thruster being positioned to impart both directions of angular momentum about each of the three axes. Each thruster pulsetrain signature is created once every processed error cycle period T1, and contains a varying number of pulses of varying widths. A negative feedback PWPF loop (2, 16, 20, 22, 24) is actuated for each of the three axes, preferably several times each T1 in order to achieve better thruster on/off resolution.

4506312, Mar 19, 1985

Sep 23, 1983

6/534403

Fred N. Chan - Atherton CA
Ernest E. Wuethrich - Santa Clara CA

Ford Aerospace & Communications Corporation - Detroit MI

G01P 344

361240

A closed-loop system for precisely regulating the speed of an electrically driven rotating body. A tachometer rotor, mechanically linked to the rotating body, is provided with p "teeth " around its periphery. A sensor produces a pulse signal upon passage of each of these teeth, to generate a cyclical tachometer signal having a frequency p times the frequency of rotation. A tachometer counter counts this signal and produces a single output pulse after every n. times. p pulses from the sensor, such that the same one of the p teeth is responsible for triggering each of the successive output pulses, and variations in spacing between teeth do not cause variations in the period of the counter output. A high frequency clock is counted by a second counter, which transfers its count to a storage register and resets upon each pulse from the tachometer counter, such that the count held by the storage register is a continuously updated, highly accurate digital representation of the period of the rotating body. A period comparator derives a speed control signal which is proportional to the inverse of the difference between the count and a digital speed command signal representative of the rotational period of the desired rotational speed.