ACTIVE NUTATION DAMPING IN DUAL-SPIN SPACECRAFT

• US 3,830,447 A
• Filed: 09/28/1972
• Issued: 08/20/1974
• Est. Priority Date: 09/28/1972
• Status: Expired due to Term

• Current Assignee: Kevin John Phillips
• Original Assignee: Kevin John Phillips
• Inventors: Phillips, Kevin John
• Primary Examiner(s): Halvosa, George E. A.
• Assistant Examiner(s): Kelmachter, Barry L.
• Application Number:
  US05/292,956
• Time in Patent Office: 691 Days
• Field of Search: 244/1SS,1SA,77SS 235/150.2,150.25,150.27 318/580,584
• US Class Current: 244/170
• CPC Class Codes: B64G 1/281 Spin-stabilised spacecraft
• CPC Class Codes: B64G 1/285 using momentum wheels
• CPC Class Codes: B64G 1/365 using horizon or Earth sensors
• CPC Class Codes: B64G 1/369 using gyroscopes as attitude sensors
• CPC Class Codes: B64G 1/38 damping of oscillations, e.g. nutation dampers
• CPC Class Codes: G01C 21/18 Stabilised platforms, e.g. by gyroscope

Abstract

A dual-spin spacecraft having a de-spun platform is arranged to vary or modulate the torque on the stabilizing member, such as a momentum wheel, by a motor whose speed is varied or modulated in accordance with a signal representing nutation motion to damp or attenutate the nutation motion substantially to zero very rapidly. The nutation motion is sensed by a suitable device such as a horizon sensor, a gyroscope, or an accelerometer. By arranging the mass distribution such that significant cross products of inertia exist, the effects of such products are utilized in a closed loop control system to effect the desired attenuation or damping. A phase shifting network is provided to shift the phase of the cyclic sensor output signal by a predetermined angle whereby optimum damping of the nutation motion is achieved.

Claims

1. A method of stabilizing an orbiting spacecraft of the dualspin type having a spin axis and a characteristic nutation frequency, and further having a platform de-spun from a motordriven spinning wheel, said wheel spinning about the spin axis of the spacecraft, said spin axis being common to said platform and said wheel, a control loop including a motor for driving said wheel and further including a first sensor and a second sensor, said first sensor oriented to sense motion of said spacecraft about a given lateral axis with respect to said spin axis, and said second sensor oriented to sense rotation of the platform of the spacecraft, about the spin axis comprising the steps of:

a. adjusting the distribution of the mass of the spacecraft so that cross products of inertia exist between at least one of the lateral axes and the spinning axis, b. sensing by said first sensor the lateral motion of the spacecraft about one of said lateral axes, c. generating a signal corresponding to the sensed lateral motion having a cyclic component at nutation frequency for controlling the torque from the motor driving the spinning wheel;

d. delaying the cyclic component of the generated signal by said first sensor at the nutation frequency of said spacecraft by an amount such that the signal from said first sensor is shifted in phase by an angle such that the first sensor signal is equivalent to a sensor signal of a sensor located on a lateral axis wherein substantially optimum nutation damping is achieved, and e. applying the delayed signal to said control loop to control the torque of said spinning wheel.

2. An attitude stabilized dual-spin spacecraft having a characteristic nutation frequency comprising:

a. a de-spun stable platform and a spinning member spinning about a non-principal axis of the platform whereby cross products of inertia about said axis exist, b. sensor means responsive to lateral motion about a lateral axis for producing a first signal representative of said motion, said first signal having a cyclic component at nutation frequency, and said sensor means being further responsive to errors in pitch angle from the spinning axis for producing a second signal representative of pitch error;

c. a closed loop control circuit including a motor for spinning said member;

d. means included in said closed loop control circuit responsive to said first signal and said second signal for varying the speed of said motor to attenuate said lateral motion and pitch error towards zero; and

e. means for delaying said component of said first sensor signal cyclic at the nutation frequency by an amount whereby the cyclic component of said first signal from the actual transverse axis of said sensor is shifted in phase by an angle such that the first sensor signal is equivalent to a sensor signal of a sensor located on a transverse axis wherein substantially optimum nutation damping is achieved.

3. The spacecraft of claim 2 wherein said sensor means includes one or more rate gyroscopes.

4. The spacecraft of claim 2 wherein said sensor means includes one or more accelerometers.

5. The spacecraft of claim 1 wherein said delaying means comprises an operational amplifier adapted to receive the first signal of said sensor means and to develop an output for controlling said motor in said closed loop control circuit.

6. The spacecraft of claim 2 wherein said delaying means comprises a phase shift netWork.