# US 9,751,645 B2 · Apparatus and method for controlling a satellite

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- Number: US 9,751,645 B2
- Document ID: US9751645B2
- Status: Granted
- Kind: B2
- Application number: 14/955,514
- Filed: 2015-12-01
- Published: 2017-03-16
- Granted: 2017-09-05
- Earliest claimed: 2015-09-10
- Assignees: Korea Aerospace Research Institute
- Applicants: Korea Aerospace Research Institute
- Inventors: Moon Jin Jeon; Sang Rok Lee; Hui Kyung Kim; Eung Hyun Kim; Seong Bin Lim; Seok Weon Choi
- Web page: https://patentgrep.com/patent/US9751645B2

## CPC

- B64G 1/244: {Spacecraft control systems}
- B64G 1/1021: {Earth observation satellites}
- B64G 1/365: {using horizon or Earth sensors}
- G05D 1/0094: {involving pointing a payload, e.g. camera, weapon, sensor, towards a fixed or moving target}
- B64G 1/26: using jets
- B64G 1/283: {using reaction wheels}
- B64G 1/32: using earth's magnetic field
- B64G 1/36: using sensors, e.g. sun-sensors, horizon sensors
- B64G 1/366: {using magnetometers}
- B64G 1/369: {using gyroscopes as attitude sensors}
- B64G: COSMONAUTICS; VEHICLES OR EQUIPMENT THEREFOR
- G05D: SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES

## Abstract

Provided is an apparatus for controlling an orbiting satellite by sensing a change in a yaw angle of the orbiting satellite and calculating a ground sample distance (GSD) based on the yaw angle. The apparatus may include a sensor configured to sense a yaw angle corresponding to yaw steering of the orbiting satellite, and a processor configured to calculate, based on the yaw angle, a GSD corresponding to a length of a pixel projected onto a planetary surface scanned by the orbiting satellite.

## Claims

### Claim 1

An apparatus for controlling an orbiting satellite, the apparatus comprising:
a sensor configured to sense a yaw angle corresponding to yaw steering of the orbiting satellite; and
a processor configured to calculate a ground sample distance (GSD) based on the yaw angle, the GSD corresponding to a length of a pixel projected onto a planetary surface of a planet being scanned by the orbiting satellite;
wherein the processor is configured to:
calculate a major axis and a minor axis of an ellipse corresponding to a trace of the projected pixel based on a change in the yaw angle;
calculate a tilt angle between a direction vector and a line of sight (LOS) vector projected onto the planetary surface; and
calculate the GSD according to the following equation:
GSD =√{square root over (a2 cos(ψ+β)2+b2 sin(ψ+β)2)}
wherein:
a is a length of the major axis;
ψ is the sensed yaw angle;
β is the calculated tilt angle; and
b is a length of the minor axis.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the processor is configured to calculate the length of the major axis and the length of the minor axis based on a radius of the planet, an altitude from the planet to the orbiting satellite, an angle at which a pixel is viewed from a scanning focal point of the orbiting satellite, and an angle between a vertical vector from the orbiting satellite to the planet and a vector from the orbiting satellite to a scanning point at which the planet is scanned.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the sensor is configured to sense a roll angle and a pitch angle of the orbiting satellite and the processor is configured to calculate the length of the major axis and the length of the minor axis using the following equation:
a
=
c
cos
⁡
(
θ
)
⁢
cos
⁢
⁢
(
ϕ
)
,
b
=
c
where a denotes the length of the major axis, b denotes the length of the minor axis, φ denotes the roll angle, θ denotes the pitch angle, and c denotes the length of the pixel.