System and method for increasing the roll offset operating range for a spacecraft

An attitude processing control system adapted to allow a spacecraft to perform missions which require spacecraft roll outside the normal roll operating range of a spacecraft earth sensor, the attitude processing and control system comprising:

• an earth sensor which operates in either a dual scan mode or a single scan mode having at least two earth sensor scans;
• control torquers;
• and
• at least one processing unit adapted to receive attitude information from the earth sensor, compute attitude, and compute attitude control commands which direct the control torquers to move the spacecraft to maintain a desired attitude;
• the attitude processing and control system being adapted to:
• move the spacecraft to a first roll position, the first roll position having a roll angle that will cause the earth sensor to have a desired standard chord;
• switch the earth sensor to single scan mode by deselecting one of the earth sensor scans, which locks the earth sensor standard chord at or near the desired standard chord;
• move the spacecraft to a second roll position, which is a desired roll offset operating position for the spacecraft;
• and
• calculate spacecraft roll at the roll offset operating position using an earth sensor roll output.

A spacecraft adapted to perform missions which require spacecraft roll outside the normal roll operating range of a spacecraft earth sensor, the spacecraft comprising:

• an attitude processing and control system comprising:
• an earth sensor which can operate in either a dual scan mode or a single scan mode having at least two earth sensor scans;
• control torquers;
• and
• at least one processing unit adapted to receive attitude information from the earth sensor, compute attitude and compute attitude control commands which direct the control torquers to move the spacecraft to maintain a desired attitude;
• the attitude processing and control system being adapted to:
• move the spacecraft to a first roll position, the first roll position having a roll angle that will cause the earth sensor to have a desired standard chord;
• switch the earth sensor to single scan mode by deselecting one of the earth sensor scans, which locks the earth sensor standard chord at or near the desired standard chord;
• move the spacecraft to a second roll position, which is a desired roll offset operating position for the spacecraft;
• and
• calculate spacecraft roll at the roll offset operating position using an earth sensor roll output.