US 2003/0171855 A1 · SPACECRAFT METHODS AND STRUCTURES WITH ENHANCED ATTITUDE CONTROL THAT FACILITATES GYROSCOPE SUBSTITUTIONS

Abstract

Methods and structures are provided that enhance attitude control during gyroscope substitutions by insuring that a spacecraft's attitude control system does not drive its absolute-attitude sensors out of their capture ranges. In a method embodiment, an operational process-noise covariance Q of a Kalman filter is temporarily replaced with a substantially greater interim process-noise covariance Q. This replacement increases the weight given to the most recent attitude measurements and hastens the reduction of attitude errors and gyroscope bias errors. The error effect of the substituted gyroscopes is reduced and the absolute-attitude sensors are not driven out of their capture range. In another method embodiment, this replacement is preceded by the temporary replacement of an operational measurement-noise variance R with a substantially larger interim measurement-noise variance R to reduce transients during the gyroscope substitutions.

Claims26

Dependent claims

A method of enhancing attitude control of a spacecraft when at least one redundant inertial-attitude sensor is substituted for at least one initial inertial-attitude sensor, the method comprising the steps of:

providing an operational process-noise covariance Q that characterizes noise variances in said initial inertial-attitude sensor and said redundant inertial-attitude sensor;
in response to attitude measurements Y from at least one absolute-attitude sensor and attitude-rate measurements Yr from said initial inertial-attitude sensor, generating a spacecraft attitude estimate Xatt with a Kalman filter that determines a gain K with an operational measurement-noise covariance R and an error covariance P that is updated with said gain K and extrapolated with said operational process-noise covariance Q wherein said operational measurement-noise covariance R characterizes noise variances in said absolute-attitude sensor;
temporarily replacing said operational process-noise covariance Q in said generating step with an interim process-noise covariance Q that is substantially greater than said operational process-noise covariance Q;
subsequent to said replacing step, substituting said redundant inertial-attitude sensor for said initial inertial-attitude sensor in said generating step;
subsequent to said substituting step, restoring said operational process-noise covariance Q and removing said interim process-noise covariance Q in said generating step;
and
in response to said spacecraft attitude estimate Xatt, controlling the attitude of said spacecraft.

4 more elements

A spacecraft configured for enhanced attitude control when at least one redundant inertial-attitude sensor is substituted for at least one initial inertial-attitude sensor, the spacecraft comprising:

a satellite body;
an attitude control system that includes:
a) at least one initial inertial-attitude sensor in said attitude control system;
b) at least one redundant inertial-attitude sensor;
and
c) at least one absolute-attitude sensor in said attitude control system;
at least one solar panel carried by said body to provide power to said attitude control system;
and
at least one data processor in said attitude control system that is programmed to perform the steps of:
a) providing an operational process-noise covariance Q that characterizes noise variances in said initial inertial-attitude sensor and said redundant inertial-attitude sensor;
b) in response to attitude measurements Y from at least one absolute-attitude sensor and attitude-rate measurements Yr from said initial inertial-attitude sensor, generating a spacecraft attitude estimate Xatt with a Kalman filter that determines a gain K with an operational measurement-noise covariance R and an error covariance P that is updated with said gain K and extrapolated with said operational process-noise covariance Q wherein said operational measurement-noise covariance R characterizes noise variances in said absolute-attitude sensor;
c) temporarily replacing said operational process-noise covariance Q in said generating step with an interim process-noise covariance Q that is substantially greater than said operational process-noise covariance Q;
d) subsequent to said replacing step, substituting said redundant inertial-attitude sensor for said initial inertial-attitude sensor in said generating step;
e) subsequent to said substituting step, restoring said operational process-noise covariance Q and removing said interim process-noise covariance Q in said generating step;
and
f) in response to said spacecraft attitude estimate X, controlling the attitude of said spacecraft with said attitude control system.

13 more elements

A spacecraft configured for enhanced attitude control when at least one redundant inertial-attitude sensor is substituted for at least one initial inertial-attitude sensor, the spacecraft comprising:

a satellite body;
an attitude control system that includes:
a) at least one initial inertial-attitude sensor in said attitude control system;
b) at least one redundant inertial-attitude sensor in said attitude control system;
and
c) at least one absolute-attitude sensor in said attitude control system;
at least one solar panel carried by said body to provide power to said attitude control system;
and
at least one data processor in said attitude control system that is programmed to perform the steps of:
a) in response to attitude measurements Y from at least one absolute-attitude sensor and attitude-rate measurements Yr from said initial inertial-attitude sensor, generating a spacecraft attitude estimate Xatt with a filter that corrects said attitude estimate Xatt with a correction that is the product of an operational gain and a residue which is the difference between said attitude estimate Xatt and successive attitude measurements Y;
b) temporarily replacing said operational gain in said generating step with an interim gain that is substantially greater than said operational gain;
c) subsequent to said replacing step, substituting said redundant inertial-attitude sensor for said initial inertial-attitude sensor in said generating step;
d) subsequent to said substituting step, restoring said operational gain and removing said interim gain in said generating step;
and
e) in response to said spacecraft attitude estimate Xatt, controlling the attitude of said spacecraft.

12 more elements

Dependencies are inferred from the claim text.

Spacecraft methods and structures with enhanced attitude control that facilitates gyroscope substitutions

Life of this patent

Spacecraft methods and structures with enhanced attitude control that facilitates gyroscope substitutions

Life of this patent

Abstract

Claims26