Microsatellite Precision Guidance, Navigation, and Control Concepts

Measuring systems based on multiple numbers and types of optical sensors connected by a single optic fiber are highly desirable for microsatellites applications because they exhibit significant advantages over traditional systems, such as micro-miniature size, light weight, low power consumption, passive (no electrical signals), resistant to RFI/EMI interference, high precision, high sensitivity, wide bandwidth, elimination of interconnecting electrical wires, environmental ruggedness, etc. Unfortunately, current commercially available optical sensors and systems do not meet the high performance requirements within the mass, volume and power constraints of this solicitation. VIP Sensors proposes to develop a silicon micromachined (MEMS) optical accelerometer configured as a single and / or multiple axis unit to measure very precise low levels signals. They are Fabry-Perot interferometer based sensors built with special mirrors using innovative design concepts that make possible the serial concatenation of multiple and different type optical sensors on a single optic fiber using Wave Division Multiplexing techniques. There are two optical sensors types pertinent to this solicitation, the Fabry-Perot interferometer and the Bragg Grating. The extrinsic nature of the first type allows optimization of the sensor's mechanical structure; but unfortunately they require expensive bulky time multiplexed electronics. Fiber grating types may use wave division multiplexing techniques, but their intrinsic configuration does not allow for optimization of the sensor's mechanical structure to achieve the accelerometer's required high performance. VIP Sensors' unique proposed approach exhibits the serial interconnection of multiple sensors and sensor types typical of the Bragg Grating sensors and the flexibility to form mechanical structures attributed to extrinsic Fabry-Perot sensors; i.e. it combines the best attributes of both of these traditional sensors. The overall objective of Phase I is to develop a detailed concept design of a high performance MEMS optical accelerometer that can be packaged as a single and triaxial transducer to be used for guidance and navigation as well as for engine and structural condition monitoring of microsatellites. Prototype units will be built and tested in Phase II. VIP Sensors proposes to use a Variable Capacitor (VC) type of structure since its designs are well known and are commonly used for accelerometers. Instead of measuring the capacitance (which changes in proportion to acceleration) with an electrical excitation signal, VIP Sensors proposes to measure the capacitor plates' gap with light. The capacitor plates become the parallel mirrors of the Fabry-Perot interferometer cavity. This design approach improves the high performance of the highly successful VC accelerometer while eliminating all of the bias and sensitivity stability problems introduced by the electrical system. It becomes a passive senso