"Software Fault Tree Analysis (SFTA) is a top-down approach to failure analysis which begins with thinking about potential failures or malfunctions (What could go wrong?) and then thinking through all the possible ways that such a failure or malfunction could occur. Fault Tree Analysis (FTA), is often used by the hardware teams to identify potential hazards that might be caused by failures in hardware components or systems, but with the SFTA, the software isn’t considered the hazard, but it can be a cause or contributor when considered in the context of the system."
"The Software Failure Modes and Effects Analysis (SFMEA) is a bottom up approach where each component is examined and all the possible ways it can fail are listed. Each possible failure is traced through the system to see what effect it might have on the system and to determine if it results in a hazardous state. Then the likelihood of the failure and the severity of the system failure can be considered."
But, to the earlier post, these are driven by hard requirements; specifically adherence to NASA STD 7150.2 and NPR 7150.2. Developers/contractors can tailor/waive them with pre-approval but, in general, they tend to go in the direction of less requirements, not more. This may all be moot because I think Voyager pre-dates any of those requirement documents and I'm not sure what existed in the late 1970s.
Here's how I would describe the possible analysis approaches in broad terms.
* Start from the hazard of being pointed in the wrong direction and work backwards to identify the causes, forming a tree.
* Start from the event of commanding the wrong direction and work forwards to identify mitigations or the lack thereof, also forming a tree.
* Start from looking at a component or subsystem, list all the ways it can fail without regard for the application, and then consider the application work up towards the causes/events.
* Close any gaps between the top-down and bottom-up approaches.