Apparatus and method for controlling a satellite

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.