Inertial Upper Stage navigation algorithms evaluation

The Inertial Upper Stage is a Space Shuttle-deployed vehicle taking payloads from low earth orbit to geosynchronous and other orbits, and incorporates a redundant inertial measurement unit containing five gyros and five accelerometers in a strapped down, skewed orientation. The gyro and accelerometer outputs are provided to redundant, on board digital computers to conduct sensor motion compensation, failure detection and isolation, and navigation in an earth-centered inertial coordinate system. Two representations of the flight software algorithms are under evaluation in preparation for the first payload-carrying flight: a FORTRAN nonreal time version for a scientific computer, and a JOVIAL version compiled for the flight computer. Results to date on nominal and off-nominal simulation runs are meeting navigation algorithm error allocations and generating correct responses to sensor error simulations for the redundancy algorithms.