Damien Wo (JH304), Fan Kaiqi (JH402), Pua Ek Hoe (JH302)

Title of the Project:Deployment of CubeSat Solar Panel Using Shape-Memory Polymer

By:Damien Wo (JH304), Fan Kaiqi (JH402), Pua Ek Hoe (JH302)

National Junior College

Mr William Phua

Nanyang Technological University

Deployment of CubeSat Solar Panel Using Shape-Memory PolymerDamien Wo (JH304), Fan Kaiqi (JH402), Pua Ek Hoe (JH302) Abstract The recent discovery of the concept of 4D printing allows for printed objects to self-assemble into 3D structures. This can be done so right off the 3D printer using Shape-Memory Polymers (SMP) which are able to temporarily alter its shape under heat stimulus, exhibiting its shape-memory effect. With this useful technology, we can replace the traditional CubeSat solar panel deployment by printing parts which are able to self-assemble into another different shape under the stimulus of radiation from the Sun, thereby aiding in the deployment of solar panels.

Background and Purpose of Research Area The basic cube satellite (CubeSat) is a type of research spacecraft called nanosatellites with a volume of exactly one litre. Due to its low-cost, short development time and the ease of deployment, the CubeSat has become increasingly popular to launch satellites built using off the shelf electronics. It has been used extensively on space research, geographical information gathering, and communication applications. According to research and the National Aeronautics and Space Administration (NASA), there has been numerous launches of CubeSat over the past 10 years, and many of them were successfully deployed [1,2]. Since CubeSats have been conceived, traditional CubeSat solar panel deployment have relied on simple aluminium or stainless steel torsion springs to deploy the solar panel array once in orbit. In transit into orbit, the solar panels are pressed against the side of the CubeSat with the torsion springs compressed. When in orbit, a nichrome wire with high resistance is heated up using on board batteries, allowing for a thermal knife to cut through the nichrome wire. When the wire is cut, elastic potential energy stored in the torsion springs during transit is released, allowing the solar one array to achieve a deployed state. However, based on research, the traditional usage of torsion springs may not always guarantee a successful launch of the satellite. For example, spring drives must use a minimum torque ratio of four [3]. If the torque ratio is incorrect, the satellite would be unable to reach its deployed state, therefore resulting in deployment failure. The primary goal of this project is to utilise shape-memory polymers (SMP) together with 3D printing to deploy the solar panel array, replacing the traditional method of deployment mentioned above. 3D printing can be made used of in many different ways, and there are various applications for such technologies, including architecture, aerospace, dental and medical industries. Based on research, there have been successful launches of satellite with 3D printed parts [5]. However, the addition of another dimension is something that has just been recently discovered. 4D printing allows materials to self-assemble into 3D structures. This concept was initially proposed by a faculty member of Massachusetts Institute of Technology, Skylar Tibbits [6]. 4D printing includes an added capability of embedded transformation from one shape to another, directly off the 3D printer. This can be easily done by utilising SMP. (b)(a)

SMP are polymeric smart materials which can exhibit a radical change from a rigid polymer to a very elastic state, then to a rigid state again. It can be deformed to other shapes upon a stimulus, without degradation of the material. SMP exhibiting a shape-memory effect have both a visible, current (temporary) form and a stored (permanent) form. They hold the major advantage of high elastic deformation, straining up to 200% and even more for most types of polymers. [4] Additionally, SMPs are also easy to actuate, such as by heating using either the sun radiation or electric heating. Through heating, deformation and then cooling, a part made of SMP can easily have its shape altered temporarily, exhibiting its shape-memory effect (Figure 1). This is otherwise known as the thermally-induced shape-memory effect (SME), which is the capability of a material to change its shape in a predefined way in response to heat [10]. This shape change is the entropy-driven recovery of a mechanical deformation, which can be obtained via an exertion of external stress, then fixed temporarily by physical crosslinks [10], thereby allowing for an SMP structure to remain in its temporary form. However, SMP are stable only at a certain temperature range. In this case, a glass transition temperature (Tg) has to be reached before the material can become relatively soft, allowing for free deformation and random twisting via rotations about backbone bonds of the polymer while maintain a maximum entropy and a minimal amount of internal energy while deformation occurs [4]. Figure 1: Picture of SMP materials in its original shape (a) and deformed shapes(b).

Thus, we can apply this concept to CubeSat solar panel deployment by printing SMP structures which are able to self-assemble into another different shape under the stimulus, which in our case will be radiation from the Sun, in order to aid in the transformation from a stored state to a deployed state in space. This not only eliminates the need for highly complex deployment mechanisms, but also deployment-control system and massive launch canisters [9]. Research Method and Materials We used SketchUp software to make and design our SMP structures which were to be printed, as shown in Figure 2. The type of SMP we are using for our project is the single-component SMP which uses Fullcure720 as its single-component material. It is a type of semi-translucent photopolymer for standard plastics simulation. It combines high dimensional stability with surface smoothness, and also allows for easier control of the transformation temperatures. There is a wide range of applications, including visualization of liquid flow; colour dying; medical applications; artistic and exhibition modelling.

(i) (ii)Figure 2: Template of designed SMP structure in (i) side view and (ii) top view

For our structures to be printed, Polyjet 350, a 3D printer was used (Figure 3). Dimensions of the printed structures were 30mm by 40mm by 1mm. It took 20 minutes for 3 of the similar structures (Figure 2) to be printed by the 3D printer which must be heated up to 70C before printing can commence. The printer makes use of the selected SMP (Fullcure 720) material to print out the designed structures. To test out our structures, we first heated a beaker of water to 60C using a heating plate. A thermometer was used to measure the temperature of water. Once the temperature of water is at 60C, we immersed our structure into the beaker of water. The thermometer was used to ensure that the temperature of water remains constant at 60C throughout this process. Due to its size and weight, the structure may float on the surface of the water. Thus 2 glass rods were used to hold the structure down and ensure that it was fully immersed into the water throughout this process. The printed structure was allowed to be immersed in water for 6 minutes before it was carefully taken out with a pair of tweezers and then placed on a smooth, flat surface. Deformation was made by using a pair of tweezers. The structure was pressed together in the horizontal direction until it collapses together (Figure). After cooling down for a minute, the structure will remain in its deformed state. This represents the state of the SMP structure before deployment occurs in space. Solar panels, as represented by thin shaded plastic sheets (Figure) will be folded as shown in Figure. Figure 3: Picture of Polyjet 350 3D printer used

Results and Discussions

Conclusion

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