Chapter 9.4.6: INERTIAL SYSTEMS TECHNOLOGIES: Navigation Computer and Software Requirements

9.4.6 Navigation Computer and Software Requirements

Inertial navigation systems operate under conditions of acceleration, shock, and vibration that may preclude the use of hard disks or standard mounting and interconnect methods. As a consequence, INS computers tend to be somewhat specialized. The following sections list some of the requirements placed on navigation computers and software that tend to set them apart.

9.4.6.1 Physical and Operational Requirements These include

1. Size, weight, form factor, and available input power.
2. Environmental conditions such as shock/vibration, temperature, and electromagnetic interference (EMI).
3. Memory (how much and how fast), throughput (operations per second), wordlength/precision.
4. Time required between power-on and full operation, and minimum time between turnoff and turnon. (Some vehicles shut down all power during fueling, for example.)
5. Reliability, shelf-life, and storage requirements.
6. Operating life. Some applications (e.g., missiles) have operating lifetimes of minutes or seconds, others (e.g., military and commercial aircraft) may operate nearly continuously for decades.
7. Additional application-specific requirements such as radiation hardening.

9.4.6.2 Operating Systems Inertial navigation is a real-time process. The tasks of sampling the sensor outputs, and of integrating attitude rates, accelerations and velocities must be scheduled at precise time intervals, and the results must be available after limited delay times. The top-level operating system which prioritizes and schedules these and other tasks must be a real time operating system (RTOS). It may also be required to communicate with other computers in various ways.

9.4.6.3 Interface Requirements These not only include the operational interfaces to sensors and displays but may also include communications interfaces and specialized computer interfaces to support navigation software development and verification.

9.4.6.4 Software Development Because INS failures could put host vehicle crews and passengers at risk, it is very important during system development to demonstrate high reliability of the software. INS software is usually developed offline on a general-purpose computer interfaced to the navigation computer. Software development environments for INS typically include code editors, crosscompilers, navigation computer emulators, hardware simulators, hardware-in-theloop interfaces, and specialized source-code-online interfaces to the navigation computer for monitoring, debugging and verifying the navigation software on the navigation computer. Software developed for manned missions must be acceptably reliable, which requires metrics for demonstrating reliability. In addition, real-time programmers for INS do tend to be a different breed of cat from generalpurpose programmers, and software development cost can be a significant fraction of overall system development cost [28].

9.4.6 Navigation Computer and Software Requirements

Inertial navigation systems operate under conditions of acceleration, shock, and vibration that may preclude the use of hard disks or standard mounting and interconnect methods. As a consequence, INS computers tend to be somewhat specialized. The following sections list some of the requirements placed on navigation computers and software that tend to set them apart.

9.4.6.1 Physical and Operational Requirements These include

1. Size, weight, form factor, and available input power.
2. Environmental conditions such as shock/vibration, temperature, and electromagnetic interference (EMI).
3. Memory (how much and how fast), throughput (operations per second), wordlength/precision.
4. Time required between power-on and full operation, and minimum time between turnoff and turnon. (Some vehicles shut down all power during fueling, for example.)
5. Reliability, shelf-life, and storage requirements.
6. Operating life. Some applications (e.g., missiles) have operating lifetimes of minutes or seconds, others (e.g., military and commercial aircraft) may operate nearly continuously for decades.
7. Additional application-specific requirements such as radiation hardening.

9.4.6.2 Operating Systems Inertial navigation is a real-time process. The tasks of sampling...