deployable reflectarray

It was previously determined that the best way to coil the folded antenna would be to spool it between and around two rollers, cinching the middle, as shown in figure 1. My task was to design a mechanism that would unroll the coiled reflectarray into the flat deployed configuration. which entails spinning the rollers (or drums) to uncoil the array, then removing the rollers to allow the antenna to unfold on its own. 

Through the initial prototype of the uncoiling mechanism, it was determined that the best way to control the uncoiling motion would be to incorporate a tensioned membrane that co-coils with the reflectarray, providing a constant tension force that helps the reflectarray wrap tightly around the coiling drums and prevents buckling. This membrane is shown in red in figure 1, while the unfolding reflectarray is in blue.

Through my ten weeks of mechanism research, design revisions, and prototyping, I came up with the new revised design shown in figure 2.  This design retains the two larger central drums that cinch the reflectarray and the two external, thinner drums that hold the tensioned membrane. During deployment, a motor spins the central drums about the center axis to uncoil the reflectarray. Meanwhile, the external cylinders remain fixed and spool up the membrane, retaining tension with constant force springs. After the array is fully uncoiled, the drums are ejected away from the center using frangibolts (explosive bolts often used in space applications), and the array is allowed to completely unfold. 

As part of my design process, I also conducted deformation analysis on a variety of parts based on the expected loads on the mechanism. For example, I calculated the expected beam bending load on the external drums due to the high tension force of the membrane, and analyzed the torsion load on the central axle. In addition, I conducted a small-scale trade study of the actuator options to determine the one best suited for the ejection. 

This experience was my first design challenge where I had full ownership over the process, and it was an incredibly educational project. Primarily, I learned to start from requirements and systematically structure the open-ended design challenge into a series of smaller, clearer steps. I also learned to iteratively apply mechanical analysis to improve upon a design. I am quite proud of my final design and my journey to it. An animation of my final mechanism design deploying the reflectarray is shown below.