Figure 1. Faulhaber stepper motor and respective location on the NEA Scout SSD  Incorrect Electrical Inputs  During consultation with the motor vendor, the team learned that the SSD’s electrical inputs needed  investigation. The prototype control board had a single step input, commanding the running speed without  ramping. This requires more current to instantaneously accelerate the motor to operational speeds. The  overcurrent provided a “false positive”:  overpowering the motors produced more torque than the datasheets  and designs allowed. The overcurrent lasted for the 15-minute deployment duration and showed no  evidence of failure through about 50+ prototype tests. However, it did give a false sense of confidence that  the smaller motors could produce the required torques due to the gross overcurrent. To correct the  overcurrent input, the board designer reconfigured the algorithms to include a gradual ramp rate which  reduced the heat output. It should be noted that this input change saved a potential failure at the next  thermal vacuum test (This error nearly crippled the development of another NEA Scout subsystem, the  Active Mass Translator and is discussed at length in “Testing and Maturing a Mass Translating Mechanism  for a Deep Space CubeSat”). Had the board not been reprogrammed, the motor may have passed ground  testing, hiding the issue until later in the program development. Mechanical Interference and Wear  There were clear signs of interference and wear on most of the rotating components within the deployer.  As the SSD was deconstructed, each part was inspected and any wear and debris was photographed. It  was clear that the as-designed gaps had closed either during assembly or operation. Some of these gaps  were 0.25 mm or less and resided between stiff structural plates and thin, rotating flanges (Figure 2, 3).   The flanges deformed during spooling and/or deployment and contacted their neighboring structural  components. This produced gouges, aluminum dust and removed the chemical conversion coating from  the contacting surfaces. Images of the damage are shown in Figures 4 and 5.   The interferences had three main causes. First, CAD models were made to the desired values and the  associated clearances respected a “perfect” construction. Areas showing reasonable clearances in the  models did not represent potential over or undersized components. Had the models been sized to their  least desirable extremes, the areas susceptible to interference would have been more obvious.  Furthermore, the tolerance analysis did not include a minimum clearance requirement on the rotating  features, so even if the parts were made to specification, any deformation would have caused damage.  Sadly, there was also no quality inspection on the EDU components so we are not sure that the EDU  components even met the drawing requirements.  Second, the rotating flanges were too thin to resist loads from the boom coils and deformed. We did not  understand the spring energy in the booms and that the thin flanges would be in the spring energy’s load  path. The flanges and gears were not stiff enough to resist and deflected through the as-designed gaps  into the structural components.   NASA/CP—2018-219887 325