STABLE EQUILIBRIUM ORIENTATION OF A SPACECRAFT WHICH CONTAINS A MOMENTUM WHEEL
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
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The orientation of a spacecraft when it is in a stable equilibrium state is studied. The spacecraft contains a single momentum wheel which stores angular momentum. The axis of the wheel is not necessarily parallel to a principal axis of the spacecraft. For an arbitrary but fixed speed of the wheel relative to the spacecraft body, it is shown that there may be one, two, or three stable equilibrium points. At each of these points, the body may spin about an axis which is fixed in both spacecraft and inertial coordinates. The orientation of this axis in spacecraft coordinates can be determined from expressions in this report. A threshold can be determined such that, if the speed of the wheel relative to the spacecraft is larger than this threshold, there is only one stable equilibrium point. This information can be used to determine the eventual orientation of the spacecraft provided it is designed such that, if it becomes seriously misoriented, the momentum wheel drive motor automatically holds the wheel speed to a predetermined value.
- Unmanned Spacecraft