Fault-tolerant inertial navigation system

A fault-tolerant inertial navigation system, comprising:

• only two independent inertial navigation units, each of said inertial navigation units measuring at least one of a plurality of navigational variables, such variables including position, velocity, and orientation, and each of said inertial navigation units comprising a plurality of single degree of freedom navigational instruments including at least three linear force sensors and three angular change sensors, any two of said linear sensors and any two of said angular change sensors of either unit aligned other than co-linear;
• and, all three of said linear sensors, and all three of said angular change sensors positioned in different planes;
• each of said inertial navigation units producing a set of independently derived navigational solutions at each of their respective outputs, said independently derived navigational solutions providing estimates of error parameters indicative of the performance of each sensor in each of said navigation units;
• means for comparing said independent navigational solutions of each of said navigation units and detecting any significantly degraded performance of either of said navigation units, by contrasting said estimates of error parameters of each instrument in one navigation unit with the estimates of error parameters in the other navigation unit;
• whereby, one of said navigation units, indicating such degraded measurement performance, is isolated and identified as to being faulty.