Position aided evader maneuvering re-entry vehicle navigator

• US 5,355,316 A
• Filed: 03/24/1989
• Issued: 10/11/1994
• Est. Priority Date: 03/24/1989
• Status: Expired due to Fees

• Current Assignee: Northrop Corporation
• Original Assignee: Northrop Grumman Corporation
• Inventors: Knobbe, Edward J.
• Primary Examiner(s): Swann, Tod R.
• Application Number:
  US07/328,208
• Time in Patent Office: 2,027 Days
• Field of Search: 364/453, 364/454, 364/456, 364/457, 364/433, 364/449, 364/423, 364/424.01, 342/107-109, 342/120, 342/450, 342/462, 244/3.2, 244/160, 244/176, 244/179
• US Class Current: 701/220
• CPC Class Codes: F41G 7/36 using inertial references
• CPC Class Codes: G01C 21/1652 with ranging devices, e.g. LIDAR or RADAR

Abstract

A navigation system 12 for an evasive maneuvering reentry vehicle (EMRV) 10 includes a three-axes strapdown inertial navigator 14 which includes RLGs or other types of gyroscopes and also accelerometers. An altimeter, such as a radar altimeter 16, which is normally provided on the EMRV 10, provides an output (h) to the navigation system 12, the output being expressive of the altitude of the EMRV 10 from the earth'"'"'s surface. The altitude measurement output (h) is processed by a statistical filter, such as a Kalman filter 18, in conjunction with the inertial solution (X) from the navigator 14. The output of the filter 18 is an estimated inertial correction which is combined with the inertial position and velocity output of the navigator 14 at a block 20 to yield a corrected position and velocity output. It is shown that a single altitude measurement is sufficient to derive three position and three velocity compensations for the EMRV 10.

Claims

1. In an evasive maneuvering atmospheric reentry vehicle, navigation apparatus comprising:

three-axis strap-down inertial navigation means having an output expressive of a position and a velocity of the vehicle;

radar altimeter means having an output expressive of an altitude of the vehicle above the surface of the earth;

Kalman filter means, having a first input coupled to the output of the inertial navigation means and a second input coupled to the output of the altimeter means, for generating an output expressive of an estimated correction to the vehicle position and to the vehicle velocity in accordance with the expression;

##EQU2## where [K_X K_X ]^T are six scalars related to gains of the Kalman filter,

(h) is the altimeter means output,

X is the position output of the inertial navigation means,

X is the velocity output of the inertial navigation means,

X_ALT is the inertial navigation means altitude solution,

(h-X_ALT) is a scalar difference between the altimeter means output (h) and the inertial navigation means altitude solution,

X is the corrected vehicle position, and

X is the corrected vehicle velocity;

the navigation apparatus further comprising summation means, having a first input coupled to the output of the navigation means and a second input coupled to the output of the Kalman filter means, for summing the output of the navigation means and the output of the generating means to produce a corrected vehicle position X, a corrected vehicle velocity X and a guidance position error .increment.X, in accordance with

space="preserve" listing-type="equation">.increment.X=(X-X).

2. In an atmospheric reentry vehicle, navigation apparatus comprising:

inertial navigation means having an output expressive of a position X, and a velocity, X, of the vehicle, and a position output X_ALT as an inertial navigation means computed altitude;

altimeter means having an output (h) expressive of an altitude of the vehicle above a reference point;

means including a Kalman filter, having a first input coupled to the output of the inertial navigation means and a second input coupled to the output of the altimeter means, for generating an output expressive of an estimated correction to the vehicle position and to the vehicle velocity computed from the difference in altitude inertial altitude between the pure inertial solution and the altimeter output (h); and

means, having a first input coupled to the output of the navigation means and a second input coupled to the output of the generating means, for combining the output of the navigation means and the output of the generating means to produce a corrected vehicle position, X, and a corrected vehicle velocity, X,

in accordance with the expression ##EQU3## where [K_X K_X ]^T are six scalars related to gains of the Kalman filter and (h-X_ALT) is a scalar difference between the altimeter means output (h) and the inertial navigation means altitude solution.

3. Navigation apparatus as set forth in claim 2 wherein the output of the combining means is expressed as a vehicle position guidance error, .increment.X, in accordance with the expression .increment.X=(X-X).

4. In an atmospheric reentry vehicle, a method of determining a correction between an inertially determined position of the vehicle and an actual position of the vehicle, comprising the steps of:

determining an inertially generated vehicle position, X, including an inertially generated vehicle altitude, X_ALT, above a reference point;

measuring an altitude (h) of the vehicle above the reference point;

generating an estimated correction to the vehicle position as a function of at least a difference between the measured altitude and the inertially generated altitude by applying the determined inertially generated position and the measured altitude to a Kalman filter; and

combining the estimated correction with the inertially generated vehicle position to obtain a corrected position of the vehicle in accordance with the expression ##EQU4## where [K_X K_X ]^T are six scalars related to gains of the Kalman filter and (h-X_ALT) is a scalar difference between the altitude (h) and the inertially generated altitude.

5. A method as set forth in claim 4 wherein the vehicle position guidance error is given by .increment.X in accordance with the expression

6. In an atmospheric reentry vehicle, navigational apparatus for determining a correction between an inertially determined position of the vehicle and an actual position of the vehicle, comprising:

means for determining an inertially generated vehicle position, X, including an inertially generated vehicle altitude, X_ALT, above a reference point;

means for measuring an altitude (h) of the vehicle above the reference point;

means for generating an estimated correction to the vehicle position as a function of at least a difference between the measured altitude and the inertially generated altitude by applying the determined inertially generated position and the measured altitude to a Kalman filter; and

means for combining the estimated correction with the inertially generated vehicle position to obtain a corrected position of the vehicle in accordance with the expression ##EQU5## where [K_X K_X ]^T are six scalars related to gains of the Kalman filter and (h-X_ALT) is a scalar difference between the altitude (h) and the inertially generated altitude.