Systems and methods for tracking power modulation

Abstract

Apparatus and methods determine the rotational position of a spinning object. A satellite positioning system can be used to determine the spatial position of an object, which in turn can be used to guide the object. However, when the object is spinning, such as an artillery shell, then the rotational orientation should be known in order to properly actuate the control surfaces, such as fins, which will also be spinning.

1 . (canceled) 
     
     
         2 . An apparatus comprising:
 a projectile antenna up estimator configured to:
 receive at least a roll phase and roll rate of an amplitude modulation of a signal from a first space vehicle, wherein the amplitude modulation is caused by spinning of a projectile; 
 receive an azimuth angle associated with the first space vehicle; and 
 determine a first state of a spin of the projectile for a first time based at least partly on the roll phase, roll rate, and the azimuth angle. 
   
     
     
         3 . The apparatus of  claim 2 , wherein the projectile antenna up estimator is further configured to receive a roll acceleration of the amplitude modulation of the signal from the first space vehicle, wherein the first state of the spin is further determined based on the roll acceleration. 
     
     
         4 . The apparatus of  claim 2 , further comprising a next up time estimator configured to estimate a future time when the antenna of the projectile will be pointing up based on information derived from the first state. 
     
     
         5 . The apparatus of  claim 2 , further comprising a current roll estimate generator configured to:
 extrapolate a second state of the projectile for a second time based on the first state and the first time; and   estimate a third time when the antenna of the projectile will be pointing up based at least partly on the second state.   
     
     
         6 . The apparatus of  claim 2 , wherein the projectile antenna up estimator is further configured to:
 receive roll phase and roll rate of an amplitude modulation of a plurality of signals from a plurality of space vehicle, wherein the amplitude modulation is caused by spinning of the projectile;   receive azimuth angles associated with the plurality of space vehicles;   determine a first plurality of states of the spin of the projectile based at least partly on the roll phase, roll rate, and the azimuth angle for each of the plurality of signals;   estimate a plurality of future times when the antenna of the projectile will be pointing up; and   combine at least a portion of the plurality of future times to generate an index for flight control.   
     
     
         7 . The apparatus of  claim 6 , wherein the projectile antenna up estimator is further configured to: receive roll acceleration of the amplitude modulation for the plurality of signals from the plurality of space vehicles, wherein the first plurality of states of the spin are further determined based on the roll acceleration for each of the plurality of signals. 
     
     
         8 . The apparatus of  claim 6 , wherein the projectile antenna up estimator is further configured to combine the at least portion of the plurality of future times by averaging. 
     
     
         9 . The apparatus of  claim 6 , further comprising a current roll estimate generator configured to extrapolate a second plurality of states of the projectile for a current time based on the first plurality of states, wherein the plurality of future times are estimated based at least partly on the second plurality of states. 
     
     
         10 . The apparatus of  claim 6 , further comprising a measurement window configured to filter out measurements such that the at least portion of the plurality of future times that are combined correspond to the future times corresponding to signals received with an azimuth angle between 45 degrees and 135 degrees. 
     
     
         11 . The apparatus of  claim 6 , wherein the projectile antenna up estimator comprises a Kalman filter. 
     
     
         12 . A method of generating spin information for flight control of a projectile, the method comprising:
 receiving at least a roll phase and roll rate of an amplitude modulation of a signal from a first space vehicle, wherein the amplitude modulation is caused by spinning of a projectile;   receiving an azimuth angle associated with the first space vehicle; and   determining a first state of a spin of the projectile for a first time based at least partly on the roll phase, roll rate, and the azimuth angle.   
     
     
         13 . The method of  claim 12 , further comprising:
 receiving a roll acceleration of the amplitude modulation of the signal from the first space vehicle;   wherein the first state of the spin is further determined based on the roll acceleration.   
     
     
         14 . The method of  claim 12 , further comprising estimating a future time when the antenna of the projectile will be pointing up based on information derived from the first state. 
     
     
         15 . The method of  claim 12 , further comprising:
 extrapolating a second state of the projectile for a second time based on the first state and the first time; and   estimating a third time when the antenna of the projectile will be pointing up based at least partly on the second state.   
     
     
         16 . The method of  claim 12 , further comprising:
 receiving roll phase and roll rate of an amplitude modulation of a plurality of signals from a plurality of space vehicle, wherein the amplitude modulation is caused by spinning of the projectile;   receiving azimuth angles associated with the plurality of space vehicles;   determining a first plurality of states of the spin of the projectile based at least partly on the roll phase, roll rate, and the azimuth angle for each of the plurality of signals;   estimating a plurality of future times when the antenna of the projectile will be pointing up; and   combining at least a portion of the plurality of future times to generate an index for flight control.   
     
     
         17 . The method of  claim 15 , further comprising:
 receiving roll acceleration of the amplitude modulation for the plurality of signals from the plurality of space vehicles;   wherein the first plurality of states of the spin are further determined based on the roll acceleration for each of the plurality of signals.   
     
     
         18 . The method of  claim 15 , wherein combining comprises averaging. 
     
     
         19 . The method of  claim 15 , further comprising:
 extrapolating a second plurality of states of the projectile for a current time based on the first plurality of states;   wherein the plurality of future times for when the antenna of the projectile will be pointing up are estimated based at least partly on the second plurality of states.   
     
     
         20 . The method of  claim 15 , wherein the at least portion of the plurality of future times that are combined correspond to the future times corresponding to signals received with an azimuth angle between 45 degrees and 135 degrees. 
     
     
         21 . The method of  claim 12 , wherein determining comprises using a Kalman filter.