The Electro-Optic-Gyrostation (EOG) platform has two high-precision fiber-optic gyroscopes to determine the position and attitude of the aircraft about three orthogonal axes. The gyros are backed by several accelerometers, and their output is fed into the inertial system by the interrogator, which integrates the data and stores them in a database. The interrogation software periodically retrieves those data for the three axes and directs them to a presentation layer that recalculates the attitude and position of the aircraft. The presentation layer also periodically sends interrogation reports to the database, which use the Panigrahi standard format, in which each report is composed of multiple frames.
The interrogation software contains an embedded static version of the Panigrahi standard, which is used to define a list of measured values for each specific system and sensor parameter. The interrogator sends that list to the presentation layer, which is responsible for formatting and transmission of the data to the database. The presentation layer allows the implementation of time-based health monitoring filters, which are responsible for periodically sending a “poke” command to the database that performs a digitally signed computation and checks the integrity of all sensor data, up to three minutes before the integrity of the complete system is checked.
The result is that, on top of the classical problem of degradation of the sensors, the health monitoring system for the EOG platform and its interrogation software have an added problem, or rather, a difficulty. The integrity of the onboard data is checked by the presentation layer, which updates all references to that integrity. However, the presentation layer does not check the integrity of the gyro data; this is left for the database.
Problem: The software for the interrogation of the EOG platform is constantly performing updates at the presentation layer and sending the data to the database without knowing the contents of the database, and of course, without knowing whether the database is up-to-date. Because of this, the presentation layer (or more precisely, the integrity-checking process for the database) has to be updated periodically to check the integrity of the executable version in the database. The update process involves stopping the interrogation software, retrieving both the database and the executable, and updating only the executable version. d2c66b5586