Design of Solar Panel Deployment Mechanism for a 1U CubeSat

AliMurtaza KothawalaPradip BobadeGuided by: Aniket Marne, Onkar Chaugule and Pranjal Naik

ABSTRACTMajor of the many limitations that a 1U CubeSat has, is the scarce availability of on-board power. The task aimed at designing a deployable solar mechanism for a 1U CubeSat which would work independently without consuming on-board power. A torsion spring loaded hinge attached to one face of the satellite. The number of such mechanisms were be 6. The body of the CubeSat still carried the regular solar panels on walls thereby increasing the power generation. A crucial aspect of this task was based on the material selection and design to ensure safe operation throughout the life of the CubeSat. To achieve an effective design, structural analysis methods were applied in addition to failure criteria methods. The whole design was meticulously done after considering the probable mechanisms that work out considerably well for a CubeSat. Design was tested for angular motion, vibrations and also motion simulation was conducted to ensure realization of task on installation. A prototype for the mechanism was to be realized for a 1U CubeSat and the same concept was extendable to 2U and 3U satellites. With the use of a secondary hinge, two panels could be deployed from one face.

INTRODUCTIONStandardization of small satellites have opened new areas of exploration for academic institutions, private industry and other agencies to test and conclude on a payload and design concept without going for a large scale investment. The CubeSats provide a platform to test and gain important insight about the possibilities and potential of space. This satellites being miniature ones, the power availability is solely on the mercy of solar flux falling on the solar panels. This panels are body mounted and cant do much of help since they dont have any pointing or maneuvering capability of their own. Use of deployable solar panels can and have in the past actually amplified this ability of solar flux collection by means of deployable solar panels, with or without maneuvering capabilities. This task meant to be completed in a short duration of 15 days was aimed at designing, testing and fabricating deployable solar panels for a 1U CubeSat. The task came with a handful of challenges since the work was to be done from zero grounds. It began from collection of relevant literature and understanding the problem well. After careful consideration and thought, torsion spring mounted on a shaft and hinge mechanism was considered for final design. The torsion hinge proved to be the most viable option considering the constraints offering simplicity and compactness required for the task. The design for spring and hinge, material selection and angle of deployment characteristics were studied and final design was prepared on PRO/ENGINEER Software. The simulation was tried on SolidWorks of which knowledge fell short of the minimum criteria.

APPROACH AND DEESIGN

Background ResearchEssential it was to study the problem statement in detail and understand the task well. A large amount of research material was studied to gain adequate understanding of the subject. The exploration revealed that actuation mechanisms such as coil springs, Shape Memory Alloys (SMA), spiral sings, electric motor, torsion bar spring, flexible joints/struts, etc. were at disposal. For the damping mechanisms we had spiral spring which took a large area, electric motor posing similar barriers as discussed earlier, rotation dampers which have fluids used in them posing a risk of leakage, Belleville springs having large volume requirement and complex design, rubber damper which was indigenous and the torsion spring in hinge which was the simplest, less volume consuming and one shot solution for the task.

Other ConsiderationsThe design was to meet the requirements of space constraints of a 1U CubeSat and still have the flexibility to be extended for a 2U or a 3U CubeSat. The available space for the panels including hinge would be (as per the CubeSat Design Specifications (CDS)) 127 mm. The panels on the ends i.e. on the side of 100 mm were to be mitered to a length of at least 10 mm and same width. The design didnt have any rails on the 4 vertical sides and the hinge straps were attached on diagonally opposite ridges on the opposite sides of the CubeSat.

Final Conceptual DesignOwing to the constraints vis. shortage of time, size limitations of a 1U CubeSat and lack of prior experience in the mechanisms involving electrical applications, further parameters were considered and torsion spring integrated in to a hinge could answer the problems. The mechanism offered simplicity, light weight, low profile, and flexibility for extension to a bigger CubeSat. This in turn eliminates power consumption, complexity on accounts of gears, linkages and time consuming and inflexible design. The spring characteristics and design were a function of torque required for stability, material selection, weight of the solar panel and angle of deployment. In addition, hinge characteristics were based on clearance required, thread engagement and body weight it will put up. For latching the panels a simple solution by using a fishing line to hold down was used. For testing purpose a temporary solution was developed to test the deployment mechanism. For this purpose a circuit was designed in which a resistive wire, was used in a loop type shape through which the fishing line was passed. Once the circuit was switched on the resistive wire melted the fishing line and the panels are deployed. The circuit diagram can be seen in the figure. The circuit is self-descriptive, as can be seen that a supply voltage is connected to the resistive wire and the resistive wire is connected with the MOSFET. One of the legs of MOSFET is connected to a 180 resistor. The switch is connected to the microcontroller which is shorted when a 3.3V is applied. The fishing line passes through a loop of the resistive wire and when the circuit is switched on the current passing through the resistor heats it up and melts the wire.Figure 1Schematic diagram for release mechanism

Material Selection:The material for the spring is based on the factors like strength, working temperatures, Modulus of Elasticity, availability in the local market, etc. Hence, spring steel (ASTM A228) was used owing to the aforementioned factors and its space heritage and popularity. The material for hinge remains the undisputed Al6061. The Aluminum alloy is suggested by the CubeSat Design Specifications and has following advantages over others: It has high ductility and stiffness to weight ratio It is cheap Has lowest density, Magnesium being the exception Has good stiffness, fracture toughness and strength enough to achieve the space objectives Has corrosion resistance and fatigue strength It has good mechanical properties and exhibits good weldability It has been popular in the space missions of the past (including many CubeSats like QuakeSat, UCISAT1, TechEdSat to name a few) and has an impressive space heritage. The material of solar panel has not been considered but the weight considerations and other parameters were taken keeping in view the SP-L-S1U-002-CS 1U CubeSat SIDE High Efficiency Solar Panel from Clyde Space Company.Figure 2- A Representation of one panel attached to the body of CubeSat

CALCULATIONSSpring Design-The spring was designed on a trial and error approach. Our main aim is to achieve a F.O.S of 2 and taking all the precautions and detailing into considerationThe spring is to open at an angle of 135 degrees, but to ascertain that the spring doesnt move from its set position, the design is done for a 145 degree such that some deficit energy will keep the panel pushed and wont let it come back or produce undesired to and fro motion.Nomenclature:D = mean diameter of spring (mm)Di = inner diameter of spring (mm)Do= outer diameter of spring (mm)d = diameter of spring wire (mm)b =bending stress in spring (N/mm2)T= Torque = angle at final leg positionLarm = Length of spring arm (mm)l = length of spring body (mm)n = number of active coil turnsks = stiffness factor of spring (N-mm/rad) Assumptions: To calculate the spring parameters some assumptions were made which are as follows: Final Leg Position final: 145(degrees) Stressed Leg position stressed: 0(degrees) Spring index C = 10Panel weight approximately equals = 2N (calculated taking into consideration standard solar panel weights and aluminum panel on which panels are mount)Material properties of spring: Type: Spring Steel (ASTM A228, Music wire)Max. Operating Temp.: 120 (C) Youngs modulus of elasticity: 210, 000 (N/mm2)Calculations:Taking yield strength as 60% of tensile strength available for 1.5mm diameter material i.e. 0.6 2275 N/mm2 = 1365 N/mm21365/2= 682.5 N/mm2 taking F.O.S as 2Also, Acting torque = 200 N-mm considering a double panel suspended from one face.

Formulae:1. b bending stress in spring = k*(32T/d3)2. Wahls correction factor, k = (4c2-c-1)/4(c2-c)3. Angle at final leg position, = 64TDn/Ed44. Body length of spring = (+1.5) 5. Stiffness factor, ks = (ED4)/ (64Dn)

Table below shows the value of calculated design parameters using above formulae:

Design ParametersValues

b (N/mm2)652.5

d (mm)1.5

D (mm)15

Di (mm)13.5

Do(mm)16.5

T (N-mm)200

(degrees)145 or 2.53 radian

Larm (mm)25

l (mm)23.85

n14.40

K (N-mm/rad)80

Hinge Design:The design of hinge takes into account only thickness of hinge enough to account for thread engagement for screws and edge distances and clearance. The dimensions are given in the diagram.The design for screw shows impractical diameters 0.2mm and so, hence their diameter is taken as 1mm. Two screws on each hinge strap will secure solar panel and CubeSat body.

CRITICAL REVIEW AND CONCLUSIONSThe task has brought about crucial points which we need to acknowledge both at technical and personal level. The task involves a simple design yet a comprehensive understanding of the various parameters affecting the whole system needs to be studied. This gives the slight hint of what creating is all about. The scheduling failed to meet the required standards to accomplish the task completely. Study of orientation of satellite was done but the implementation wasnt. The structural analysis part also missed out. This paves the way for generating a quest for new things, learning a range of drawing, design and analysis software. The essence lies in action and applying acquired knowledge of various components, mechanisms, designs to create something novel and futuristic. The design is potential in catering to the desired requirements and can be refined to involve vibration damping, orientation/maneuvering capability, etc.

FUTURE SCOPEThe preliminary design has been done for the deploying mechanism. It can be installed on a 1U CubeSat and can be extended to 2U and 3U CubeSats without much of a problem. The design is a basic one but can guide, deploy and damp to a certain extent. More sophisticated requirements can be met by redefining some parameters and working anew.

REFERENCES1. Fabio Santoni , Fabrizio Piergentili , Serena Donati, Massimo Perelli , Andrea Negri Michele Marino An innovative deployable solar panel system for CubeSats, Elsevier Journal, Acta Astronautica, 2014, Vol. 952. Patrick Hohn- Design, Construction and Validation of an articulated solar panel for CubeSats3. A.M. Watt and S. Pellegrino, Rigid Deployable Solar Array4. M. Mirshams1 , S. Moradi , A. Ebrahimi- Design Of Deployment Mechanism Of Solar Array Of A Sample Satellite And Investigation Of Deployment On Control Attitude Of Satellite, Department of Mechanical Engineering, K.N.Toosi University5. Nathan K. Walsh- Development of A Deployable 3U CubeSat Solar Panel Array, College of Engineering, University of Hawaii at Mnoa, Honolulu, HI 968226. Jose Miguel Encinas Plaza, Jose Antonio Viln, Fernando Aguado Agelet, Javier Barandiarn Mancheo, Miguel Lpez Estvez,Cesar Martnez Fernndez and Fany Sarmiento Ares-Xatcobeo: Small Mechanisms for CubeSat Satellites Antenna and Solar Array Deployment7. Michelle A. Mojica- Structural Subsystem Design, Analysis and Optimization For A Nanosatellite8. Hamza Baig- Integrated Design of Solar Panels Deployment Mechanism For a Three Unit CubeSat9. https://www.wikipedia.org10. https://www.planetspring.com11. https://www.tribology-abc.com12. https://www.nasa.gov13. https://www.clyde-space.com14. https://www.isro.org