Calibration of ship attitude reference

• US 7,451,022 B1
• Filed: 12/28/2006
• Issued: 11/11/2008
• Est. Priority Date: 12/28/2006
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Luk-Paszyc, Jerzy W., Stetson, John B.
• Primary Examiner(s): Hellner; Mark
• Application Number:
  US11/647,053
• Publication Number:
  US 20080269965A1
• Time in Patent Office: 684 Days
• Field of Search: 701/220, 701/222, 701/13, 701/3, 701/4, 244/164
• US Class Current: 701/13
• CPC Class Codes: B63G 9/00 Other offensive or defensive arrangements on vessels against submarines, torpedoes, or mines
• CPC Class Codes: G01C 21/025 with the use of startrackers
• CPC Class Codes: G01C 21/1656 with passive imaging devices, e.g. cameras
• CPC Class Codes: G01C 21/203 Specially adapted for sailing ships
• CPC Class Codes: G01C 25/005 initial alignment, calibration or starting-up of inertial devices
• CPC Class Codes: G01S 3/7867 Star trackers navigation using star trackers G01C21/025

Abstract

A ship includes a star tracker mounted on a platform stabilized in ENU by the inertial navigation system (INS). The line-of-sight (LOS) of the star tracker is directed toward two separated stars, and the LOS difference angles are noted. The angles are processed to generate vector triads representing geodetic (ephemeris) and navigation system attitude. The triads are processed to generate a coordinate transformation matrix. The transformation matrix is separated into systematic error and reference attitude error. The reference attitude error is summed with the inertial navigation system attitude to generate corrected ENU attitude. The corrected attitude is used as a reference for shipboard sensors, to reduce errors when the sensor data is linked to other platforms.

Claims

1. A method for calibration of an attitude reference apparatus, said method comprising the steps of:

providing an inertial navigation system for a surface ship, which navigation system provides local reference of the ship'"'"'s attitude relative to East, North, and UP;

providing a star tracker mounted on a platform stabilized by said local reference of the ship'"'"'s attitude, said star tracker being for comparing the azimuth and elevation angles between the line-of-sight of said star tracker and each of two selected stars, to thereby generate first and second azimuth and elevation differences;

controlling said line-of-sight of said star tracker in response to ephemeris of said two selected stars;

processing said azimuth and elevation angles to determine first and second vector triads representing ephemeris and the navigation system attitude;

processing said first and second triads to determine a coordinate transformation matrix;

separating said coordinate transformation matrix into systematic error and reference attitude error; and

combining the reference attitude error with the navigation system attitude to generate calibrated navigation system attitude.

2. A method for calibration according to claim 1, further comprising the steps of:

generating sensed data referenced to said calibrated navigation system attitude; and

transmitting said sensed data referenced to said calibrated navigation system attitude to a remote location.

3. A method according to claim 1, wherein said step of processing said azimuth and elevation angles to determine first and second vector triads representing ephemeris and the navigation system attitude comprises the steps of:

determining the star tracker local azimuth and elevation angles;

determining the star tracker attitude triad from the local azimuth and elevation angles; and

determining the geodetic reference attitude triad from ephemeris and the local azimuth and elevation angles.

4. A method according to claim 3, wherein:

said step of determining the star tracker local azimuth and elevation angles comprises computing

Az_s^o=Az_e^o+Δ

Az_s^o

El_s^o=El_e^o+Δ

El_s^o 

 

(11)

where;

Δ

Az_s^o is the azimuth difference angle measured by the star tracker between the star tracker line-of-sight to one star; and

Δ

El_s^o is the elevation difference angle measured by the star tracker between the star tracker line-of-sight to that one star.

said step of determining the star tracker attitude triad from the local azimuth and elevation angles comprises computing

q=v

r=q×

u/∥

q×

u∥

s=q×

r 

 

(20)

where

u, v are the unit LOS vectors to selected stars

q, r, s are unit vectors representing the orthogonal attitude triad

where

$\begin{array}{cc}v=\left[\begin{array}{c}X<br><br><br><br>1\\ Y<br><br><br><br>1\\ Z<br><br><br><br>1\end{array}\right];<br><br><br><br>u=\left[\begin{array}{c}X<br><br><br><br>2\\ Y<br><br><br><br>2\\ Z<br><br><br><br>2\end{array}\right];<br><br><br><br>q=\left[\begin{array}{c}{q}_x\\ q_y\\ q_z\end{array}\right]<br><br>;<br><br><br><br>r=\left[\begin{array}{c}{r}_x\\ r_y\\ r_z\end{array}\right];<br><br><br><br>s=\left[\begin{array}{c}{s}_x\\ s_y\\ s_z\end{array}\right],& \left(21\right)\end{array}$
X1=Cos(Elv) Sin(Azv) X2=Cos(Elu) Sin(Azu)

Y1=Cos(Elv) Cos(Azv) Y2=Cos(Elu) Cos(Azu)

Z1=Sin(Elv) Z2=Sin(Elu) 

 

(22),

and said step of determining the geodetic reference attitude triad from ephemeris and the local azimuth and elevation angles is performed by computing attitude matrix M_R

$\begin{array}{cc}{M}_R=\left[\begin{array}{ccc}{q}_{\mathrm{Rx}}& r_{\mathrm{Rx}}& s_{\mathrm{Rx}}\\ q_{\mathrm{Ry}}& r_{\mathrm{Ry}}& s_{\mathrm{Ry}}\\ q_{\mathrm{Rz}}& r_{\mathrm{Rz}}& s_{\mathrm{Rz}}\end{array}\right]<br><br><br><br>\mathrm{and}<br><br><br><br>\mathrm{matrix}<br><br><br><br>M_s;<br><br>& \left(23\right)\\ M_S=\left[\begin{array}{ccc}{q}_{\mathrm{Sx}}& r_{\mathrm{Sx}}& s_{\mathrm{Sx}}\\ q_{\mathrm{Sy}}& r_{\mathrm{Sy}}& s_{\mathrm{Sy}}\\ q_{\mathrm{Sz}}& r_{\mathrm{Sz}}& s_{\mathrm{Sz}}\end{array}\right]& \left(24\right)\end{array}$

related by the transformation;

AM_R=M_S 

 

(25).

5. A method according to claim 1, wherein said step of combining the reference attitude error with the navigation system attitude to generate calibrated navigation system attitude comprises the steps of computing matrix

$\begin{array}{c}{\stackrel{\_}{A}}_{\mathrm{ENU}}\end{array}$

1 / N ⁢

∑

i = 1 N ⁢

⁢

A ENU , i ( 34 )

where

A_ENUi=A_SKi−

A_EST, i=1 . . . n

for correcting the ship ENU to geodetic ENU.

6. A method for calibration of an attitude reference apparatus, said method comprising the steps of:

providing an inertial navigation system for a surface ship, which navigation system provides local reference of the ship'"'"'s attitude relative to East, North, and UP;

providing a star tracker mounted on a platform stabilized by said local reference of the ship'"'"'s attitude, said star tracker being for comparing the azimuth and elevation angles between the line-of-sight of said star tracker and each of two selected stars, to thereby generate first and second azimuth and elevation differences;

controlling said line-of-sight of said star tracker in response to ephemeris of said two selected stars;

processing said azimuth and elevation angles to determine first and second vector triads representing ephemeris and the navigation system attitude, respectively;

processing said first and second triads to determine a coordinate transformation matrix;

separating said coordinate transformation matrix into systematic error and reference attitude error;

generating sensed data referenced to said navigation system attitude; and

correcting said sensed data by said coordinate transformation matrix.