1998 - Draper Laboratory

maintained in a rigid structure, whereas the FOG has its path infiber, making the FOG fundamentally much more susceptible toenvironmental effects such as temperature changes. Forcomparable performance applications, the selection between theFOG and the RLG will very likely depend on the scale-factorrequirements.Figure 4. Micromechanical pendulousrebalance accelerometer.against today’s technology, given comparable technicalrequirements, this new class of solid-state inertial sensorsbecomes the winner because the basis of selection is almostalways cost. A vision of the inertial instrument field for relevantmilitary applications for the near-term is shown in Tables 1 and 2for the gyro and accelerometer, respectively.The performance application region of about 0.01-deg/h bias driftfor gyros is expected to shift from current RLG applications toFOGs. The RLG is an excellent instrument, but itsmanufacturing is heavily dominated by precision machiningprocesses and alignment requirements, which force its costs toremain relatively high. It is quite possible that FOG performanceimprovements will allow applications in strategic missileapplications where the performance requirements exceed 0.001deg/h. However, one particular area the RLG is expected to retainits superiority is scale factor. The laser gyro has its optical pathTable 1. Near-term gyro requirements vs applications.The tactical lowest performance end of the gyro applicationspectrum will be dominated by micromechanical inertial sensors.These could be, for example, gyros and accelerometersphotolithographically constructed in silicon or quartz andsubsequently etched in very large numbers as a single batch. Themilitary market will push the development of these sensors forapplications such as “competent” and “smart” munitions, aircraftand missile autopilots, short time-of-flight tactical missileguidance, fire control systems, radar antenna motioncompensation, “smart skins” using embedded inertial sensors,multiple intelligent small projectiles such as flechettes or even“bullets,” and wafer-scale INS/GPS systems.The potential commercial market for micromechanical inertialsensors is orders of magnitude larger than any contemplatedmilitary market. The application of micromechanical gyrotechnology to the automobile industry is one case where, forexample, a true skid detector requires a measure of inertial rate inorder to operate successfully. Products designed for this industrymust be inexpensive and reliable, both characteristics ofsolid-state technology. Many other micromechanical inertialsensor applications exist for automobiles such as airbags, braking,leveling, and GPS-augmented navigation systems. Additionalcommercial applications can be found in products such ascamcorders, factory automation, general aviation, and medicalelectronics. The performance of the micromechanicalinstruments will likely continue to improve as more commercialapplications are found for this technology.Table 2. Near-term accelerometer requirements vs applications.σµ σINS/GPS Technology Trends for Military Systems5