Once the team was comfortable with the boom deployments, the EDU sails were deployed. Two sails were  produced for EDU activities:  a Mylar sail and a colorless polymer-1 (CP1) sail. Both sails were 86 m2 in  size, and the CP1 version was built as flight-like as possible. During the deployments, the team updated  procedures with boom support information, electrical inputs, sail attachment methods, and mechanical  fixtures. These tests proved to be the most eye-opening tests to date.   Stepper Motor Deployment Failure and Motor Sizing Lessons Learned  Prior to the solar sail deployer (SSD) random vibe test, the engineering team conducted a boom-only  deployment and learned that the existing stepper motor was undersized. This became a large setback that  led to a drastic SSD mechanical redesign, lengthy coordination with the motor vendors, and a long list of  failure causes. It was clear that the undersized motor was performing properly with suitable electrical inputs,  but it was unclear why the booms would not deploy.   After investigating, the team determined that the torque requirement was vastly underestimated and a larger  motor was needed. The design team then set about to redesign the deployer to house a larger stepper  motor. Unfortunately, the SSD had no volume to spare. The motor volume was specifically tailored the  previous motor with no margin. After weeks of redesigning 4 of the 5 primary structural components, the  larger motor—just 4-mm taller than the undersized motor—was accommodated.  The rest of the team conducted a failure analysis in parallel with the redesign effort. After a month of  discussion and investigation, a list of possible causes was created and the team commenced to find the  root cause or causes. The team investigated the control board settings, the test setup and the deployer.  Luckily, the SSD’s redesign activities required complete deconstruction allowing the designer to inspect the  assembly alignments and each part for wear, deformation, and/or any other visible damage. Wear and more  severe damage was discovered and documented. Analysis comparing the CAD models, mechanical  drawings, additively manufactured plastic prototype, and as-built EDU uncovered 6 contributing errors. The  causes are listed in the order they were discovered with the final cause, number six, identified as the root  cause.  1. The motor was undersized and lacked volume margin to allow for a larger version. 2. The prototype control board was overpowering the motors, producing more torque than expected. 3. The system was unknowingly susceptible to mechanical interference and wear. 4. Internal friction was grossly underestimated. 5. The boom spooling operation was prone to large irregularities and damaged other components. 6. The team drew too many comparisons between the plastic prototype and EDU. Each item above will be discussed and presented as a lesson learned.  Undersized Motor Volume Allocation The mechanical design team determined years before the EDU tests that stepper motors would power the  SSD. There were few motors to choose from in a desirable form factor—about 15 mm in diameter or less— and steppers would produce the most torque per unit volume. Significant prototype testing with 3D printed  components, friction estimation and torque calculations were made to select the first motor: a Faulhaber  AM1524 with a 91:1 planetary gearbox (Figure 1). After selecting the motor, the designer matured the SSD  design without allocating any significant clearances between the motor and other structural components.  The motor was boxed in.   Just as it is common practice to design mechanical interfaces with extra material in the event larger  fasteners are needed, the design team learned that this cautious practice applies to motor volume allocation  as well. A new motor just 4-mm taller than its predecessor required a large redesign effort including major  changes to 80% of the SSD structural components. All of the redesign efforts and cost could have been  avoided if the motor volume allocation had just 10% of height margin.  NASA/CP—2018-219887 324