HAWAIISAT-1 MODULAR STRING SOLAR CELL LAYOUT PROCEDURAL PLAN

Transcription

1 HAWAIISAT-1 MODULAR STRING SOLAR CELL LAYOUT PROCEDURAL PLAN Raynel U. Corpuz (Team Members: Reid Yamura and Paul Liggni) Project Advisors: Elwood Agasid, NASA ARC; Lloyd French and Jeremy Chan, HSFL National Aeronautics and Space Administration (NASA): Ames Research Center Project For: Hawaii Space Flight Laboratory (HSFL) ABSTRACT Solar cell design has always been a critical part in satellite design. Designing an efficient solar cell design improves the mission and flight success. There are many different approaches in designing a solar cell layout for small satellites. Based on the chosen solar cell layout design implemented, certain tradeoffs follow the design as well. Choosing to design a solar cell layout that uses a series approach produces more voltage at the output, but it may fail due to one solar cell being damaged. This in turn ultimately takes out the entire string because of it being in series. However, we can take on a whole new solar cell layout design by implementing a series and parallel approach using a modular design developed at NASA Ames Research Center (NASA ARC) which will be implemented on a small satellite the Hawai i Space Flight Laboratory (HSFL) is building (HawaiiSat-1). This entails lower voltage at the output, but decreases the risk of losing the entire string which still makes it capable for the satellite to generate power.

2 Table of Contents Introduction...3 Motivation...3 Requirements...3 Facility Requirement...3 Material Requirement...4 Layout Procedure Requirement...6 Layout Procedure...6 Preparation...6 Assembly...7 Storage/Handling/Transportation...8 Testing...8 Performance Results...8 Conclusion...8 Appendix...9 Acknowledgements...11 References...11

3 INTRODUCTION Solar cell design with the aid of NASA Ames modular string solar cell design will be the main topic discussed in the report. We first begin by explaining what types of materials are involved in developing the design. Some important material characteristics that we have run across were the solar cells, structural substrate, insulation layer, and miscellaneous components. In our learning of modular string solar cell design, we began by asking employees with in the small satellite division group in NASA Ames that were experienced on the subject matter at hand because the concept was new to us. By having meetings with NASA Ames staff members experienced with the modular string solar cell development, we got a general idea on how to go about implementing the design to HawaiiSat-1. The report will cover a comprehensive overview of the materials required, process in fabrication, and test procedures used of the new modular string solar cell design. MOTIVATION The motivation for fabricating a modular string solar cell design is that in the modular form, it can be used on future small satellites without any adjustments being made. Allowing modularity, the new design can be mass produced to fit future small satellites. The new design incorporates a solar cell layout in parallel and series to avoid the loss of an entire string. Solar cell design is a crucial part in the small satellites architecture because it is the power generation for the whole system. The solar panels will be the major source of gathering power to power up the small satellite components. By implementing the new modular string solar cell design approach, we can lower the some of the risks of a small satellite. REQUIREMENTS Facility Requirement All facilities used will be documented accordingly and be used to make all materials readily available for fabrication. 1. Basic Machine Shop (a) Cutting aluminum honeycomb sheets (b) Drill press to drill holes in honeycomb sheets 2. Clean Room (a) Area to assemble and fabricate the new solar panel design 3. Shock and Vibration Test Facility (a) To be determined Material Requirement The following is a list of materials that will be needed in the fabrication of the layout. 1. Solar Cells (a) Space grade BTJM Solar Cells from Emcore or equivalent

4 2. Structural Substrate (a) Hexcel aluminum honeycomb i. Dimensions: Approximately 3/8 inch thick, to be determined Width and to be determined Length. Dimensions should conform to EPS-Module- ICD.pdf (current HawaiiSat-1 solar panel module design). ii. Material Properties A. Plating surface: phosphoric acid anodized aluminum or similar properties to prevent corrosion B. Honeycomb must be perforated to prevent expansion of the honeycomb in space C. Deflection tolerance is to be determined (b) 6061-T6 1/4 inch Al plate or equivalent material based on spacecraft s requirements. i. X by Y by Z dimensions 3. Insulation Layer (a) PCB Board made of FR4 solder mass, Gold or lead-tin plating w/ conformal coating (b) Hawaiisat-1 Solar Cell Module i. 19 BTJM solar cells in series ii. iii. Gold plated or lead tin plating used and conformal coating See figure 1 for dimensions A mm is preferred Adhesives 1. Nusil CV Adhesive (Solar cells to PCB interface). Specifications are shown in Appendix A. 2. Nusil CV-1142 Adhesive (PCB to Al interface). Specifications are shown in Appendix B. Miscellaneous Components 1. Interconnect and Grounding Wires such as Tefzel M22759/33-22 or equivalent space grade wire for low outgassing. 2. TBD screws/bolts to allow proper grounding of the aluminum honeycomb sheets (a) There will be a through hole Keenserts insert in honeycomb. (b) There will be a threaded insert in the structural side. 3. Silicon Remover (a) IPA

5 Figure 1: HawaiiSat-1 Solar Cell Module Dimensions

6 Layout Procedure Requirement In the modular solar cell layout process of HawaiiSat-1, the following requirements must be satisfied. 1. All steps of the procedural process must be completed under the supervision of someone who is familiar with the process, but not involved in the actual assembly. 2. Required documentation must be completed at each step of the process. This documentation primarily consists of the hardware tracking log and the confirmation log for each piece that is built. 3. This document must be referenced in the corresponding drawing documents for the original flight panels. 4. All materials used in the flight assembly must have a corresponding Certificate of Conformance received from the vendor. LAYOUT PROCEDURE Preparation The following is a step by step procedure for the preparation of the modular layout. 1. Solar Cell Preparation (a) Clean the table, tools, and equipment that will be used for the solar cell layout with denatured alcohol and cotton swabs. Make sure to eliminate all oxide residues and dirt that may have collected on the table and tools. (b) Use Nitrile gloves to handle solar cells with extreme care to prevent oils and FOD (foreign objects damage) from contaminating the cells. Clean solar cells, front and back, by using denatured alcohol. In each case use cotton swab to do all the cleaning. (c) Ensure that each of the connectors from the solar cells are straight and has no bends in it. Accomplish this by using a small set of pliers to clamp down and straighten the connectors. (d) Place 4 of the solar cells in series to create a string. A jig should be created to allow for 0.762mm consistent spacing between each of the cells. Use soldering iron to solder the 4 cell string when spacing requirement is met. 2. PCB Preparation (a) Acquire PCB to the desired size for use in the modular layout. (b) Use denature alcohol to clean the surfaces of the PCB. Baking and roughing of the PCB surface is not required to insure proper adhesion between materials.

7 3. Hexcel Aluminum Honeycomb (a) Cut the aluminum honeycomb to the desired specifications to be used on the modular layout. (b) Drill 6 holes into the aluminum honeycomb to secure the solar cell module to the spacecraft frame as shown in figure 1. Assembly Once all the materials are within the design specification of HawaiiSat-1, the assembly of the modular string solar cell design will take place in a class 100,000 clean room facility. By assembling the materials in a clean room, it leaves no room for foreign object damage or any damage that can occur beyond human control. 1. Clean the solar cell string and PCB with IPA using a lint-free cloth to remove FOD. 2. Apply the Nusil CV adhesive to the PCB. Use extreme care while applying because voltage degradation may occur if applied improperly. (a) Application for adhesive to surface is TBD (b) Observe proper polarity of the solar cells to the PCB (c) Use a TBD size bag of water as an evenly distributed pressure source to insure proper adhesion (d) Clean and remove excess adhesive using IPA or RPM tech silicon remover to remove any excess adhesive that may have spilled (e) Allow adhesive to cure properly i. CV cure time is 15 min at 150 degrees C 3. Solder the tabs on the solar cell string to the PCB at... TBD temp 4. Apply the Nusil CV-1142 adhesive to the aluminum honeycomb (a) Application of adhesive surface is TBD (b) Clean and remove excess or spilled adhesive using IPA or RPM tech silicon remover (c) Allow adhesive to cure properly i. Cure time is 7 days at room temp 5. Connect the modular solar panels in desired configuration (series or parallel) (a) Use Tefzel M22759/33-22 or equivalent space grade wires for electrical connections (b) Use TBD or desired connectors for electrical connections 6. Connect the TBD wires for proper grounding wires of the aluminum honeycomb

8 Storage/Handling/Transportation To be determined Testing The following will be testing that will be performed for the new modular solar cell string layout. 1. Electrical performance (solar panel analyzer or solar simulator) (a) Variation of temperature (b) Variation of incident angle on to panel (c) Metrics to record i. Open circuit voltate (Voc) ii. iii. iv. Short circuit current (Isc) Distance from lamps Power v. Luminosity vi. vii. Temperature Load at Mppt 2. Shock and Vibration Test (a) Requirements: TBD 3. Thermal Vacuum (a) Requirements: TBD PERFORMANCE RESULTS To be determined CONCLUSION In conclusion, I believe that working with NASA Ames to improve the current design on HawaiiSat-1 solar panel layout was a fruitful and knowledgeable experience. Being able to go from a 19 solar cell string in series to a modular string solar cell design has dramatically decreased some of the risks involved in satellite design. We plan to expand more on the project by learning the detailed process involved in assembling the new solar cell design. By improving the current solar cell design with the new modular string solar cell approach, we can use it on future small satellites as a default solar panel.

9 Figure 2: Nusil CV Data Sheet APPENDIX A

10 Figure 3: Nusil CV 1142 Data Sheet APPENDIX B

11 ACKNOWLEDGMENTS To be determined REFERENCES [1] Haykin S. Simon, Adaptive Filter Theory, Ed. Thomas Kailath, 4th ed., Upper Saddle River: Prentice hall, Print. (1995), Cambridge Univ. Press, Cambridge, 2001, pp Written in LaTeX Updated 26 July 2010 Updated 27 July 2010 Updated 28 July 2010 Updated 29 July 2010 Updated 30 July 2010 Updated 31 July 2010 Updated 01 August 2010 Updated 02 August 2010 Updated 03 August 2010 Updated 04 August 2010