Programming Languages Behind the Mars Sojourner Rover

The Mars Sojourner rover, which was an integral part of NASA's Mars Pathfinder mission in 1997, relied heavily on computer programming to navigate the Martian surface and perform various scientific tasks. This article delves into the programming languages used for the Sojourner rover and discusses the specific processors and software systems involved.

The Role of C and Assembly

At the core of the Sojourner rover's software system was the programming language C, specifically designed for its onboard software to enable autonomous navigation and scientific experimentation. This language was chosen for its efficiency, reliability, and robustness, making it well-suited for the complex tasks the rover needed to perform.

Although C was the primary language for the majority of the rover's software, some components required deeper, low-level hardware manipulation. These critical sections, particularly those related to time-sensitive and hardware-specific functionalities, were written in 8085 assembly code. This combination ensured that the rover could perform all its tasks accurately while maintaining flexibility and performance.

The Processor and Command Systems

The 80C85 processor served as the backbone of the Sojourner rover's computational needs. It performed all the necessary processing for the rover's operations. All the rover software, aside from a few time-critical or hardware-specific functions, was written in ANSI C. This language facilitated the development and integration of complex software systems, ensuring that the rover could operate autonomously without significant issues.

The command and telemetry communication between the Earth and the Sojourner rover were managed through modems located in both the rover and on the Pathfinder lander. The rover would request any commands sent from Earth, and when commands were not available, it would transmit the collected telemetry data to the lander, which would then forward it to Earth. Command generation and telemetry analysis were performed at the rover control workstation on Earth.

The Rover Control Workstation (RCW)

The Rover Control Workstation (RCW) was a crucial system used to control the Sojourner rover. It consisted of over 40 thousand lines of C code, supplemented by another 40 thousand lines of code using X Window Motif libraries. This system provided users with a graphical user interface for each possible rover command, enhancing usability and control.

The RCW utilized various libraries and tools for string manipulation, linked list data structures, and mathematical routines through the Tools.h and Math.h class libraries from RogueWave software. For graphical user interfaces, the Motif library's windowed sliders, buttons, and text entry widgets were extensively used. Three-dimensional visualization was achieved through the Open Inventor and OpenGL libraries, ensuring that the commands and telemetry data were displayed accurately and intuitively.

Further Reading

For more detailed information on the design of the software and I/O hardware used in the Sojourner rover's Control and Navigation Subsystem, you can refer to the following resources:

The MFEX Rover System and Operations Overview The Mars Pathfinder Rover Operations Training

These documents provide extensive information on the rover systems and are invaluable for understanding the technical aspects of the mission.

Conclusion: The Mars Sojourner rover utilized a combination of C and assembly languages to perform its tasks, with C being the primary language for its onboard software. The system was carefully designed to leverage the strengths of these languages, ensuring the rover could navigate the Martian surface and conduct scientific experiments with precision and reliability.