Persistence is the means by which data is saved and retrieved within the system. All persisted files are stored on a RAID array to provide redundant storage. InControl utilizes eXtensible Markup Language (XML) files to persist data such as telemetry and command data definitions and properties. XML files were chosen over database products such as Sybase or Oracle for several reasons. First, the performance using flat files can be a significant improvement over commercial database products. Second, versioning of the data in sections such as telemetry decommutation, alarm limits and derived algorithms such that these sections can be changed independently is much easier. For example, a new set of alarm limit XML files may be copied into the appropriate directory and utilized without changing the rest of that mission’s database file. That is more difficult to do when all processes are utilizing a database and a single table within the database must be changed offline and then moved into the online environment without affecting other processes such as commanding or decommutation. Also, use of a particular database product increases system administration costs, adds license costs and possibly forces a customer to use a product different than their preferred one.

Finally, many sites have a spacecraft fleet consisting of satellites from many satellite manufacturers. Each manufacturer often delivers a database and editing tools to go with the satellite. These tools may already be in a database product such as Sybase or Oracle and the manufacturer may periodically deliver new databases. Rather than trying to integrate with multiple database products and data definitions, InControl provides translators to convert each database into the required XML format. The translators utilize a GUI to lead the user through the process and allow differencing of data so that changes may be monitored and approved prior to use.

In order to update the online database to a new version, a translation may be done offline on either the whole database or a designated portion. Once the database files are ready, they may be placed in the appropriate directories for both the primary and redundant systems and properties may be updated to point to the new files. The necessary services (such as telemetry processing and/or command processing) may be recycled on the redundant server using a warm restart to preserve dynamic data such as limits or memorized LRVs to switch in the new databases. Only the mission and processes recycled are affected and the process takes less than 30 seconds. The same process can then be repeated for the primary server (with or without first switching control to the redundant server as desired).

During operations, some data is modified dynamically. This data must be persisted and distributed to the backup site so that it can be accessed by the redundant system in the case of failure of the primary system. InControl persists the following data for that purpose: