What are Solar Array Drive Mechanisms?

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Apr 21, 2023

Solar energy as compared to other energy sources are used for space exploration, is the predominant source of power when space missions are considered. Solar panels have become the primary source of energy for a variety of applications, including powering satellites and space probes. These panels are fitted with solar array drive mechanisms (SADM) to adjust the panel's position relative to the sun. The SADM is responsible for providing power to the solar panel, and it is also responsible for rotating the panel to ensure it is pointed directly at the sun. Photovoltaic cells are obtained in various forms based on their design of manufacturing and functionality as the forms of solar cells, solar modules, solar panels, and solar arrays. PV cells or solar cells converts solar energy into electrical energy. Solar modules are solar cells that will be mounted on a structure to be interconnected to form a module. In 1958 solar panels were first used in Vanguard 1 satellite at the time crystalline silicon panels were used because they were the only ones that were being researched, as research expanded to thin film solar panels. Gallium arsenide tinfoil panel proved to be a great replacement. It had two particular properties that made it superior to crystalline silicon, first was its degradation over time which was much lower than that of silicone-based panels. Secondarily its efficiency didn't change much with the change in temperature of the panel.

Design of Solar Array Mechanism

The engineering design needs to manage the conflicting goals, improving performance while reducing developing time and costs. In the same context, designers utilized solar energy as a clean renewable source for powering small satellites. Once the satellite is in orbit, the solar arrays are deployed to function. The optimal working conditions of the photovoltaic solar array are dependent on the angle of incident light to the normal photovoltaic solar array surface. The SADM consists of an electric motor that rotates the solar panel. It provides enough torque to move the panel without affecting its structural integrity. Solar arrays of considerable surface area are required to provide enough power for safe payload functioning and for the computer and the communication systems. Innovative designs included foldable solar arrays to minimize size and space requirements on the launching vehicle. Self-actuated deployment mechanisms utilized the stored energy in a torsion spring to drive the solar arrays during the unfolding phase after orbital insertion. In such cases, the motion has to be controlled by drag braking to reduce or eliminate the shock loading at the end of the stroke. Drag brake should be of minimum size and weight but can absorb and dissipate energy enough to make gradual deployment and smooth motion until the mechanism gets to rest at the end of the stroke, without shock loadings or reactions. Research also shows that the design of a small shoe brake can be used to control the unfolding and protect the solar panels from shock loads and damage at the end of the deployment.

Diagrammatic representation of the solar array mechanism design


Working

The SADM must also operate within a wide range of temperatures from 200°C to -100°C, to ensure it works in space’s harsh environment. This mechanism must provide precise positioning and movement, with a step size of less than 1 arcsecond. It is also designed to work for an extended period, sometimes up to 15 years.

The deployment and retraction sequence of the solar array mechanism design consists of a solar array that is launched in a particular position before the beginning of the deployment sequence, the solar array is unlatched from the rocket integrated equipment assembly mounting structure and rotated on a 4-bar linkage away from the truss structure to begin the deployment which will be positioned to look down at the tip fitting along the negative z direction of the solar array coordinate system.  The tethered pin, holding the box in the stowed position is removed and the pin will be stowed temporarily on the linkage bar. Using the tip cross member bar and a handhold on the pivot fitting to rotate the box outward 90 degrees, the lower locking strut will automatically snap closed when the box is in the fully deployed position will then replace the pin assuring that the upper blanket box is also locked in the deployed position. Successful operation is visually confirmed when each blanket box will be rotated separately then it is required to translate three feet along the tip cross member to establish the position for the second box deployment. During unlatching of the blanket box, the post-deployment tension mechanism is actuated and reduces the tension of the blanket in the tension distribution system simultaneously. The blanket restraint pins used to restrain the blanket during the launch is released. Each pin provides a visual indication of retraction by projecting a small tube out of the bottom of the box. The electrical confirmation of successful pin retraction and full unlatching is provided by limit switches the second box is unlatched in the same manner, and once both boxes are unlatched the solar array blanket is deployed by extension of the foldable articulated square truss mast. Guide wires are used to control the blanket motion throughout the deployment for the last 18 inches of mast extension, the tension distribution bar is lifted out of the blanket box providing 5 to 10 pounds of tension to each blanket full deployment is confirmed by limit switches on the fast mast. Once the mast is deployed to its full length the blanket box latches are reversed and run to their fully stowed position this allows the post-deployment tensioning system to apply the full 75 pounds of tension to each blanket confirmation of this operation is provided by the latch limit switches and the solar array is now fully deployed. The full unlatching and deployment sequence will require almost 15 minutes. One new space station solar array will supply 31.4 kilowatts to the space station power system.

The retraction of the solar array begins with the release of tension in the blanket to accomplish this the latches are driven to their unlatched position thereby activating the post-deployment tensioning mechanism. This action also positions the latches in the unlatched state so they are ready to re-latch the box. Once the array is retracted, confirmation of this operation is provided by the latch limit switches. Once tension is reduced the mast begins the retraction of the solar array, the guide wires are again required to control the blanket panels during retraction. In addition, springs embedded in the blanket assembly ensure that the solar array folds in a controlled fashion the completion of this operation is confirmed by the mast limit switches.

The solar array drive mechanism is a critical component of solar panels in space. The mechanism must provide precise and efficient movement of the panel while working in the harsh environment of space. The latest advancements in technology have improved the accuracy, reliability, and efficiency of SADMs. With the increasing demand for power in space, future designs will continue to push the boundaries of what is possible, making space exploration and research more feasible than ever before. The designs have also been proposed to maximize the overall power production, by reducing the angle between the incident light and the normal to the surface and allowing the solar array to rotate freely such that continuous solar orientation of the photovoltaic system is achieved.

Solar array drive mechanism is a predominant method used to implement on LEO micro-satellites. Therefore, a market need for the use of a solar array drive mechanism on micro-satellite platforms has been identified and designed the solar array drive mechanism that can fulfill the mission objectives defined by the market needs. The system can be adjusted such that all micro-satellite LEO altitudes can accommodate this system, with a few modifications the angular range of the system can satisfy the power requirements, and pointing accuracies of the satellite and hence a rapid development of the SADM will provide the market advantage.

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