What is the most likely reason a DC thruster at 45% command shows only 20% feedback?

The most likely reason a DC thruster, which is commanded to operate at 45%, is showing only 20% feedback can be attributed to a failure in the thruster drive system. In a dynamic positioning system, the commanded output and the actual feedback should ideally correlate closely if the system is functioning correctly.

When there is a discrepancy as significant as this—where the command is nearly doubled compared to the feedback—it suggests that there is an issue within the thruster's ability to respond to the command. This could be related to the electronic control systems that manage the power delivery to the thruster, such as a failure in the drive circuitry, instabilities in the power supply, or failures in motor windings. Any of these conditions could prevent the thruster from achieving the commanded power level, leading to the observed low feedback.

Other factors such as battery discharge or environmental influences may also impact performance, but they wouldn't typically result in a consistent and systematic discrepancy of this nature—they might lead to reduced performance overall, rather than a specific failure to respond to command levels. Therefore, the strong likelihood of a failure in the thruster drive system explains the significant difference between the command and actual thrust feedback.