Requires No External Sensorsorbit Independent High Accuracy For Limited Time Intervals Easily Done Onboard

SENSESCMANGE IN ORIENT AT ion ONLY-nd ABSOLUTE MEASUREMENT; SUBJECT TO OHIFT. SENSORS HAVE RAPIDLY MOVING PARTS SUBJECT td WEAR AND FRICTION: RELATIVELY HIGH POWER AND LARGE MASS

that affect the attitude, as listed in Table 1-2, are aerodynamic torque caused by the rapid spacecraft motion through the tenuous upper atmosphere;gravity-gradient torque due to the small difference in gravitational attraction from one end of the spacecraft to the other (the same differential force which produces tides); magnetic torque due to the interaction between the spacecraft magnetic field (including induced magnetism from the surrounding field) and the Earth's magnetic field; and solar radiation torque due to both the electromagnetic radiation and particles radiating outward from the Sun. Early investigators felt that micrometeorites might also supply a significant source of torque. However, this has been found negligible relative to the other torques, except perhaps in some unexplored regions of the solar system, such as inside the rings of Saturn.

The relative strengths of the various torques will depend on both the spacecraft environment and the form and structure of the spacecraft itself. Nonetheless, because of the form of the distance dependence of the environmental torques, the space environment for any specific spacecraft may be divided into

Table 1-2. Environmental Disturbance Torques

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