# US 2021/0199752 A1 · System and method for intercepting an exo-atmospheric target using passive ranging estimation

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- Number: US 2021/0199752 A1
- Document ID: US20210199752A1
- Status: Published application
- Kind: A1
- Application number: 15/946,063
- Filed: 2018-04-05
- Published: 2021-07-01
- Earliest claimed: 2018-04-05
- Assignees: Raytheon Company
- Applicants: Raytheon Company
- Inventors: Huy P. Nguyen; Elliot Schwartz; Eric Blake; Pradyumna Kannan
- Web page: https://patentgrep.com/patent/US20210199752A1

## CPC

- G01S 7/021: {Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals}
- F41G 7/2226: {comparing the observed data with stored target data, e.g. target configuration data}
- F41G 7/2253: {Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target}
- F41G 7/2293: {using electromagnetic waves other than radio waves}
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- F41G: WEAPON SIGHTS; AIMING (optical aspects thereof G02B)

## Abstract

A target intercept system for guiding an interceptor to a target using passive ranging includes an EO/IR sensor that provides target azimuth and elevation angles, target irradiance, target area and target length. A dual Kalman Filter architecture is implemented where, prior to a target image becoming resolved, i.e., prior to endgame, a first Kalman Filter provides guidance as a function of target azimuth and elevation angles and target irradiance measurements. After the target image becomes resolved, i.e., at endgame, a second Kalman Filter provides guidance as a function of target azimuth and elevation angles, target area and, optionally, target length, instead. The dual Kalman Filter approach improves the estimates of time-to-go by optimizing the on-board EO/IR sensor measurements at the optimal times.

## Claims

### Claim 1

A system for guiding an interceptor toward a target using passive ranging estimation, the system comprising:
an EO/IR sensing device configured to:
detect the target and output corresponding target azimuth information, target elevation information, target irradiance information, target length information, target area information and a respective validity indicator for each of the target azimuth information, target elevation information, target irradiance information, target length information and target area information;
determine that the target irradiance information is valid and the target area information is invalid only when the target is detected as a point source; and
determine that the target irradiance information is invalid and the target area information is valid only when an image of the target has been resolved,
wherein the target area information and the target irradiance information cannot both be indicated as being valid at a same time;
a passive ranging target state estimator, coupled to the EO/IR sensing device and configured to generate interceptor guidance information, comprising:
a first Kalman Filter configured to generate the interceptor guidance information as a function of the target azimuth information, the target elevation information and the target irradiance information; and
a second Kalman Filter configured to generate the interceptor guidance information as a function of the target azimuth information, the target elevation information and the target area information,
wherein the first Kalman Filter is operative to generate the interceptor guidance information only when the target irradiance information is indicated as being valid,
wherein the second Kalman Filter is operative to generate the interceptor guidance information only when the target area information is indicated as being valid; and
an interceptor guidance module, coupled to the passive ranging target state estimator, configured to control movement of the interceptor as a function of the generated interceptor guidance information.

### Claim 2 (depends on 1)

The system of claim 1, wherein the second Kalman Filter is further configured to generate the interceptor guidance information as a function of the target length information.

### Claim 3

(canceled)

### Claim 4 (depends on 1)

The system of claim 1, wherein the EO/IR sensing device is further configured to determine that the target is detected as a point source when the target is detected as a single pixel.

### Claim 5

A method of guiding an interceptor toward a target using passive ranging estimation, the method comprising:
detecting the target with an EO/IR sensing device and outputting corresponding target azimuth information, target elevation information, target irradiance information, target length information, target area information and a respective validity indicator for each of the target azimuth information, target elevation information, target irradiance information, target length information and target area information;
determining a range from the interceptor to the target as a function of one or more of: the target azimuth information, target elevation information, target irradiance information, target length information, target area information and the respective validity indicators;
determining that the range is greater than a first predetermined distance only when the target is detected by the EO/IR sensing device as being a point source; and
determining that the range is less than or equal to the first predetermined distance only when the EO/IR sensing device has resolved an image of the target,
wherein the EO/IR sensing device cannot have both detected the target as a point source and resolved the image of the target at the same time;
generating interceptor guidance information by one of:
when the determined range is greater than the first predetermined distance, implementing a first Kalman Filter configured to generate the interceptor guidance information as a function of the target azimuth information, the target elevation information and the target irradiance information; or
when the determined range is less than or equal to the first predetermined distance, implementing a second Kalman Filter configured to provide the interceptor guidance information as a function of the target azimuth information, the target elevation information and the target area information; and
controlling movement of the interceptor as a function of the generated interceptor guidance information.

### Claim 6 (depends on 5)

The method of claim 5, wherein the second Kalman Filter is further configured to generate the interceptor guidance information as a function of the target length information.

### Claim 7

(canceled)

### Claim 8 (depends on 5)

The method of claim 5, wherein determining that the range is greater than the first predetermined distance, further comprises:
indicating that the target irradiance information is valid and the target area information is invalid.

### Claim 9 (depends on 5)

The method of claim 5, wherein determining that the range is less than or equal to the first predetermined distance further comprises:
indicating that the target irradiance information is invalid and the target area information is valid.

### Claim 10 (depends on 5)

The method of claim 5, wherein the EO/IR sensing device determines that the target is a point source when the target is detected as a single pixel.

### Claim 11

A system for guiding an interceptor toward a target using passive ranging estimation, comprising:
an EO/IR sensing device configured to detect the target and output corresponding target azimuth information, target elevation information, target irradiance information, target length information, target area information and a respective validity indicator for each of the target azimuth information, target elevation information, target irradiance information, target length information and target area information;
a passive ranging target state estimator coupled to the EO/IR sensing device configured to:
determine a range from the interceptor to the target as a function of one or more of: the target azimuth information, target elevation information, target irradiance information, target length information, target area information and the respective validity indicators;
determine that the range is greater than a first predetermined distance only when the target is detected by the EO/IR sensing device as being a point source; and
determine that the range is less than or equal to the first predetermined distance only when the EO/IR sensing device has resolved an image of the target,
wherein the EO/IR sensing device cannot have both detected the target as a point source and resolved the image of the target at the same time;
the passive ranging target state estimator further configured to generate interceptor guidance information by one of:
when the determined range is greater than the first predetermined distance, implementing a first Kalman Filter configured to generate the interceptor guidance information as a function of the target azimuth information, the target elevation information and the target irradiance information; or
when the determined range is less than or equal to the first predetermined distance, implementing a second Kalman Filter configured to provide the interceptor guidance information as a function of the target azimuth information, the target elevation information and the target area information; and
an interceptor guidance control module, coupled to the passive ranging target state estimator, configured to control movement of the interceptor as a function of the generated interceptor guidance information.

### Claim 12 (depends on 11)

The system of claim 11, wherein the second Kalman Filter is further configured to generate the interceptor guidance information as a function of the target length information.

### Claim 13

(canceled)

### Claim 14 (depends on 11)

The system of claim 11, wherein determining that the range is greater than the first predetermined distance further comprises:
indicating that the target irradiance information is valid and the target area information is invalid.

### Claim 15 (depends on 11)

The system of claim 11, wherein determining that the range is less than or equal to the first predetermined distance further comprises:
indicating that the target irradiance information is invalid and the target area information is valid.

### Claim 16 (depends on 11)

The system of claim 11, wherein the EO/IR sensing device is further configured to determine that the target is a point source when the target is detected as a single pixel.