Minimization of residual spacecraft nutation due to disturbing torques

Abstract

Spacecraft nutation caused by applying attitude and/or orbit control forces to a spacecraft along an axis which does not pass through the spacecraft's center of gravity is minimized by a signal responsive control system which first operates the attitude and/or orbit control forces for a predetermined time period and automatically after an appropriate non-operating time period, the attitude and/or orbit control forces are again operated for the same predetermined time period.

What is claimed is: 
     
       1. A method for minimizing nutation in a spacecraft of the dual spin type having a spin axis and a characteristic nutation period and further having a platform despun from a spinning member, comprising the steps of: transmitting signals to spacecraft receiver means causing a receiver means output signal;   coupling said receiver output signal to logic circuit means causing a logic circuit means output signal;   activating a force generating means mounted on said platform a first time for a predetermined operating period T 1  in response to said logic circuit output signal, said predetermined operating period determined by said logic means to be a predetermined portion of said nutation period of said spacecraft;   deactivating said force generating means for a waiting period T w , in response to said logic circuit means output signal at the end of said predetermined operating period T 1  ;   activating said force generating means automatically a second time in response to said logic circuit means output signal for said predetermined operating period T 1  after said waiting period T w , wherein said waiting period, T w , is determined by: ##EQU7## where ω n  is the spacecraft nutation frequency and T 1  is said force generating means operating period.   
     
     
       2. A control system for minimizing nutation in a spacecraft of the dual-spin type having a spin axis and a characteristic nutation period, and further having a platform despun from a spinning member, comprising: receiver means included in said spacecraft for receiving signals transmitted to said spacecraft, and generating in response thereto a receiver means output signal;   logic means coupled to said receiver means and in response to said receiver output signal generating a logic control output signal; and   torque generating means mounted on said platform and coupled to said logic means and, in response to said logic control output signal, activating said torque generating means for a predetermined operating period T 1 , said predetermined period T 1  determined by said logic means to be a predetermined portion of said nutation period of said spacecraft, at the end of said period T 1  automatically deactivating said torque generating means for a predetermined waiting period T w , and at the end of said waiting period T w , automatically activating said torque generating means again for said predetermined operating period T 1 ,   wherein said waiting period, T w , is determined by ##EQU8## where ω n  is spacecraft nutation frequency and T 1  is said predetermined spacecraft operating period.   
     
     
       3. A control system according to claim 2, wherein said torque generating means is at least one thruster. 
     
     
       4. A control system according to claim 2, wherein said logic means includes a firing electronics circuit including a timer means arranged to respond to said logic output signals and to activate said force generating means for said predetermined operating period, T 1 , then automatically deactivating said torque generating means for a predetermined waiting period, T w , and then automatically activating said torque generating means again for said predetermined operating period, T 1 . 
     
     
       5. A closed loop attitude control system for minimizing nutation in a spacecraft of the dual-spin type having a spin axis and a characteristic nutation period, and further having a platform despun from a spinning member, comprising: detector means included in said spacecraft for detecting a deviation from a desired spacecraft attitude, and generating in response thereto a detector means output signal;   logic means coupled to said detector means and in response to said detector output signal generating a logic control output signal; and   torque generating means mounted on said platform and coupled to said logic means and, in response to said logic control output signal, activating said torque generating means for a predetermined .[.,.]. operating period T 1 , said predetermined period T 1  determined by said logic means to be a predetermined portion of said nutation period of said spacecraft, at the end of said period T 1  automatically deactivating said torque generating means for a predetermined waiting period T w , and at the end of said waiting period T w , automatically activating said torque generating means again for said predetermined operating period T 1 ,   wherein said waiting period, T w , is determined by: ##EQU9## where ω n  is spacecraft nutation frequency and T 1  is said predetermined spacecraft operating period.   
     
     
       6. A control system according to claim 5, wherein said torque generating means includes at least one thruster. 
     
     
       7. A control system according to claim 5, wherein said logic means include a firing electronics circuit including a timer means arranged to respond to said logic output signals and activate said force generating means for said predetermined operating period, T 1 , then automatically deactivating said torque generating means for a predetermined waiting period, T w , and then automatically activating said torque generating means again for said predetermined operating period, T 1 . .Iadd. 8. A method for reducing nutation caused by a thrust force not passing through the center of gravity of a spacecraft of the dual spin type having a spin axis and a characteristic nutation period and further having a platform despun from a spinning member, comprising the steps of: transmitting signals to spacecraft receiver means causing a receiver means output signal;   coupling said receiver output signal to logic circuit means causing a logic circuit means output signal;   activating a force generating means mounted on said platform for producing said thrust force a first time for a predetermined operating period T 1  in response to said logic circuit output signal, said predetermined operating period determined by said logic means to be a predetermined portion of said nutation period of said spacecraft;   deactivating said force generating means for a waiting period T w  in response to said logic circuit means output signal at the end of said predetermined operating period T 1  ;   activating said force generating means automatically for producing said thrust force a second time in response to said logic circuit means output signal for said predetermined operating period T 1  after said waiting period T w , wherein said waiting period, T w , is determined by: ##EQU10## where ω n  is the spacecraft nutation frequency and T 1  is   
     
     
        said force generating means operating period. .Iaddend. .Iadd. 9.  A control system for reducing nutation caused by a thrust force not passing through the center of gravity of a spacecraft of the dual-spin type having a spin axis and a characteristic nutation period, and further having a platform despun from a spinning member, comprising: receiver means included in said spacecraft for receiving signals transmitted to said spacecraft, and generating in response thereto a receiver means output signal;   logic means coupled to said receiver means and in response to said receiver output signal generating a logic control output signal; and   torque generating means mounted on said platform for producing said thrust force and coupled to said logic means and, in response to said logic control output signal, activating said torque generating means for a predetermined operating period T 1 , said predetermined period T 1  determined by said logic means to be a predetermined portion of said nutation period of said spacecraft at the end of said period T 1  automatically deactivating said torque generating means for a predetermined waiting period T w , and at the end of said waiting period T w , automatically activating said torque generating means again for producing said thrust force for said predetermined operating period T i , wherein said waiting period, T w , is determined by: ##EQU11## where ω n  is spacecraft nutation frequency and T 1  is said   
     
     
        predetermined spacecraft operating period. .Iaddend..Iadd. 10.  A control system according to claim 9, wherein said torque generating means is at least one thruster. .Iaddend. .Iadd. 11. A control system according to claim 9, wherein said logic means includes a firing electronics circuit including a timer means arranged to respond to said logic output signals and to activate said force generating means for said predetermined operating period, T 1 , then automatically deactivating said torque generating means for a predetermined waiting period, T w , and then automatically activating said torque generating means again for said predetermined operating period, T 1 . .Iaddend. .Iadd. 12. A closed loop attitude control system for reducing nutation caused by a thrust force not passing through the center of gravity of a spacecraft of the dual-spin type having a spin axis and a characteristic nutation period, and further having a platform despun from a spinning member, comprising: detector means included in said spacecraft for detecting a deviation from a desired spacecraft attitude, and generating in response thereto a detector means output signal;   logic means coupled to said detector means and in response to said detector output signal generating a logic control output signal; and   torque generating means mounted on said platform for producing said thrust force and coupled to said logic means and, in response to said logic control output signal, activating said torque generating means for a predetermined operating period T 1 , said predetermined period T 1  determined by said logic means to be a predetermined portion of said nutation period of said spacecraft, at the end of said period T 1  automatically deactivating said torque generating means for a predetermined waiting period T w , and at the end of said waiting period T w , automatically activating said torque generating means again for producing said thrust force for said predetermined operating period T 1 ,   wherein said waiting period, T w , is determined by: ##EQU12## where ω n  is spacecraft nutation frequency and T 1  is said   
     
     
        predetermined spacecraft operating period. .Iaddend..Iadd. 13.  A control system according to claim 12, wherein said torque generating means includes at least one thruster. .Iaddend. .Iadd. 14. A control system according to claim 12, wherein said logic means includes a firing electronics circuit including a timer means arranged to respond to said logic output signals and activate said force generating means for said predetermined operating period, T 1 , then automatically deactivating said torque generating means for a predetermined waiting period, T w , and then automatically activating said torque generating means again for said predetermined operating period, T 1 . .Iaddend.