SBIR-STTR Award

The innovation is to embed a MEMS IMU Sensor Chip into a reaction wheel to measure its spin rate as well as wheel attitude rate. We propose to use a reaction wheel such as the NASA Goddard reaction/momentum wheel (SMEX) because of its high degree of development and capability for static and dynamic balancing. The IMU Sensor Chip will derive stability from the inertia of the wheel resulting in greater precision and accuracy. During Phase I we propose to integrate the two entities and test the operation of the MEMS gyroscopes and accelerometers of the IMU Sensor Chip to demonstrate the benefits of the union. In addition to attitude sense and control, the combination would also improve GN&C and enable autonomous operation in GPS-denied environments.

Reaction wheels are used to stabilize satellites and to slew their orientation from object to object with precision and accuracy by varying the rotational speed of the wheels. Three or four wheels are usually used with three of them aligned along orthogonal axes. The degree to which pointing stability is achieved depends on the stability of the wheels' angular momentum vectors while spinning, which can be affected by static and dynamic unbalance contributions and other wheel construction issues. With the smaller satellites, requiring smaller wheels, the stability of the wheels will be even more challenging as the uncertainty of construction is likely to remain the same. To stabilize the smaller reaction wheels we propose to integrate a Sensor Chip containing MEMS gyroscopes and accelerometers with each reaction wheel. This allows direct measurement of the wheel motions for fine-tuning its operation. The improved wheel then becomes a means for improving IMU sensor stability for precision pointing and slewing from object to object.