When developing satellites there are going to be faults that can cause a mission to fail. Thankfully there are tools such as the Ishikawa analysis that can help us solve these faults for future missions. Since there could be a wide range of potential causes to a fault it is not feasible to investigate each one. Ishikawa analysis also known as fishbone analysis was developed by Kaoru Ishikawa in the 1960’s (1) to help identify the root cause(s) of defects and issues or a process or product.

Figure 1 Fish bone analysis

Carrying out a fishbone analysis (Figure 1) is quite simple, the fault or issue you want to solve is typed into the “effect” box at the right of the diagram. Then you create the categories for the potential causes, these categories can be “human, machine, environment, material etc”. Once you have identified your categories you then brainstorm potential causes in the relevant areas that could have led to that fault.

Figure 2 Fishbone analysis Satellite example

In our example (Figure 2) we cannot communicate with our satellite. After a short brainstorming we have a couple of potential causes ranging from inadequate training on operating the radio, failure in the radio, poor workmanship, satellite not pointing to ground station, trying to contact the wrong satellite to the sun interfering with the radio. Some of the potential causes identified won’t be correct however we may have a couple of leads to what is causing our communication problem.

5 whys

After you have identified potential causes it’s time to use 5 why’s where you ask why five times for each potential cause. This can help you identify the potential root cause. In our satellite issue we can use the satellite not pointing to ground station as our problem statement.

Problem: Satellite not pointing to ground station

• Why is it not pointing at the ground station? The satellite is not accurately positioning itself.
• Why is it not accurately positioning itself? ADCS system is not functioning properly.
• Why is the ADCS system not functioning properly? Interference between magnetorquers and reaction wheels.
• Why is there interference in the reaction wheel? The wheels are made from ferrous materials and are attracted to the magnetorquers.
• Why are the wheels made from ferrous materials? The material was selected due to it’s density and the implications of the reaction wheels and magnetorquers weren’t noticed.

In this example we could see that material selection would have met the required outgassing standards but the implication of a stainless steel wheel next to an electromagnet were never considered. It could have been overlooked as the magnetorquers and reaction wheels were tested separately therefore this issue was missed. This can also indicate that the satellite systems weren’t thoroughly tested and could also indicate an issue with the review process within the organisation.

Once you have identified some potential root causes you should develop a testing plan to test each potential cause to resolve the issue. You may need to redo your 5 why’s as your first attempt may not have been successful in identifying the root cause which is why you should always test out the end result of the investigation.

References

1. Ishikawa Diagram: A Guide. Safety Culture. [Online] [Cited: February 27, 2023.] https://safetyculture.com/topics/ishikawa-diagram/.