Southern University La ACES Team EXCELLE Experiment (Experiment For Solar Cell Efficiency) Tannus Joubert, Kristen Hypolite, Kevin James, Laquonda Johnson, Michael Johnson, Shanta McKinzie, Leslie Sanford Preliminary Design Review (PDR) March 18, 2005

Mission Objectives  Measure the light conversion efficiency  Output of an assortment of solar cells throughout various levels of the atmosphere  Results –conclude whether future La ACES experiments can be powered by the most efficient solar cells found

SCIENCE GOALS Understanding  Solar Cell Efficiency  The Solar Spectrum –Its relation to the silicon solar cell material band gap  Energy  Photons  Wasted Heat

Types of solar cells  Monocrystalline –Made from pure silicon, most efficient (~24 % in the lab), but most expensive since they are difficult to make  Polycrystalline –Less efficient (18 % in the lab)  Amorphous –Least efficient (13%), used in watches, calculators

Technical Goals  Measure the light conversion efficiency that solar cells –Research the condition the solar cells can withstand –Find the position that the sun is at the time of launch and during launch to maximize the solar power –Deal with the rotation that maybe encountered by the cord being tangled

Payload Design  The payload will be surrounded with three types of solar cells, so that energy conversion efficiencies can be compared.  DesignSubcategories:  System  Thermal  Mechanical  Electrical  Software design

Principle of Operations N-Type P-Type _ _ _ _ _ Electric Field Photon Path I Load Power output + _ VoVo

Possible challenges  Rotation effects- may be dealt with by measuring position of sun with respect to pay load  Ultra-violet radiation- Will it damage the cells or be beneficial by providing more energy?  Pendulum motion of package- will it interfere with our data?  Launching at dawn – how to maximize sunlight intake due to low position of sun?

System Interface Components   Main System:   Basic Stamp Processor   Subsystems:   Solar cells   User Interface   Real Time Clock   Analog-To-Digital Converter   Memory   Power   System Reset   Temperature Sensor

*Real Time Clock provides accurate date and time Solar cells send the charge through charge converter for signal acquisition by the multiplexer. ADC converts analog to a readable digital signal Memory must be synchronized with the ADC to process the data. User interface (Laptop) will be used to upload and download software and data. Basic Stamp Processor is used to control all data acquisition and processing. Solar Cells Charge Converter Analog to Digital Converter Basic Stamp Processor Memory Real Time Clock System Reset User Interface Multiplexer Temperature Sensor Power System Interface Components

Electrical Design  BalloonSat System –6V at 100mA –4 AA Li Batteries  Charge Controller/Converter –Convert current coming from each cell into voltage –Convert excess voltage into heat, used to keep inside of box warm –Voltage signal/readings to be passed through an 8 channel multiplexer  combine all the signals into one data stream

Electrical Design cont’d  Onboard Temperature Reading –Onboard ADC –Voltage Regular Temperature Reading –Operational Amplifier  BASIC STAMP –If memory is full Basic Stamp is able to turn itself off –Power supply regulator is already built into the circuit board –LEDs will be used to confirm operations

Electronic Flowchart SOLAR CELLS CHARGE CONVERTER MULTIPLEXER ADC RTC BASIC STAMP MEMORY

Thermal Design  Flying payload to the height of approximately 30km at the temperature of -60 o C.  Location Palestine, Texas.  Challenge is to design a payload to stay well in the range of the operating condition of the electronics.  Overheating of the solar cell

Payload Operating at -60 o C Overheating of the Solar Cells 80 o C Overheating of Electronics

Thermal Schematic Solar cells cool by radiation Mesh Inner Temp maintained to within o C with induced convection with fan Electronics generate heat Air (R) Solar Cells (R) Mesh (INS) (C) Foam Core (C, R) Inside Payload (R) (CV) Q cond Spacer Air flow (-60 o C) where R- radiation, C-conduction, CV-Convection, and INS – Insulation

Recommendations  Spacer-mesh combination to prevent scorching of foam core  May rely of rotational effects to radiate heat from the box  Test simulation will be done on electronic and payload system to determine possible thermal effects

Mechanical Design 1. Creating a payload of a low weight, high thermal stability, and a suitable degree impact resistance. Constructing a payload that will withstand such stresses is also a key factor in our design. 2. The method of attaching solar cells to the payload and interfacing them with the rest of the electronics. 3. Preflight worthiness test. We will focus on :

Mechanical Design The box concept for now is simply rectangular payload with which consist of two modules: 1.Inner module 2. Outer module

Mechanical Design The functions of the outer module are: 1. To serve as a primary encase for the second module. for the second module. 2. Provide a protective covering against acceleration, deceleration, against acceleration, deceleration, shock, and impact. shock, and impact. 3. To provide a surface for the attachment of the solar cells and framed mesh. and framed mesh. 4.To provide a barrier against the cold temperatures experienced by the payload. cold temperatures experienced by the payload. 17 cm 18 cm 15.5 cm

Mechanical Design The functions of the inner module are: 1.To provide a containment for the electronics. 2. To hold the batteries. 3. To serve as a second line of defense against impact, shock and gravitational forces. 4. To help optimize the heat transfer of the payload. 14 cm 15 cm 6 cm

Mechanical Design The solar cells will be mounted on a sheet of mesh framed with Popsicle sticks. The removable frame will then be attached to the payload by screwing the frame into half inch non- conducting standoffs that will already be attached to the box. By mounting the solar cells on this structure, the heat that will dissipate from the solar cells will be able to flow freely away from the payload. Back view of framed mesh. Front view of framed mesh. Non-conducting standoff

Mechanical Design Weight Budget of the Pay Load: Weight limit: 500 g Balloon Sat: 0.5g x 3 x 4 = 6.00 g g One monocrysitaline solar cell: Batteries:8.3 x 4 =33.3 g Inter and outer modules: 160 g g500 g - = < g g Frame Mesh Standoffs

Futuristic Payload Development  Charge Converter System  Control Solar System –Circuit  Mechanical Systems –Screws  Thermal Control System –Too Hot???  Finishing Software  Build Prototype –Find circuits that work interface with software

Payload Construction Plan  Electronics- planning, development, and implementation  Mechanical and thermal- Planning, development and implementation  Software systems  Documentations  Flight Implementation

ElectronicsMechanicalThermalSoftwareIntegrationFlight BalloonSat Basic Stamp ADC Converter Multiplexer Sensors Interfaces Foam Core Inner Module Outer Module Spacers Mesh Solar cells Electronics Modules Solar cells Mesh Foam Core ADC program Sensors Basic Stamp Control Interfaces Electronics Mechanical Thermal Software Interfaces BalloonSat Basic Stamp ADC Converter Multiplexer Sensors Interfaces

Hardware Fabrication  Solar Cells –Testing –Framework  Charge Converter Circuitry (Separate Boards) –Circuitry –Multiplexer  Box Structure –Shock and Thermal Testing –Drop Test  Battery (Power System) –Location –Interfacing to Whatever Needs Power

Integration Plan  To test the connections between electronics and software.  Stabilize Power Connection  Ensure that the Mechanical structure is able to hold the batteries, boards, and other system ancillaries.  Take Thermal Test to ensure that components are working properly due changes in temperature.

Software Implementation and Verification  The Software designed will calculate and measure the current and voltage output by the cells and store the data  The software will decide from which set of cells the signal is being read, and process each accordingly. The software will be used to calculate voltage and power produced by the cells as a function of altitude.

ADC Inputs the Data Solar Cell Identifier 1 Not 1 2 Reads the ADC value Reads the ADC value Calculates the Voltage Solar Cell Identifier Solar Cell Identifier 3 Stores into Memory End Time Stamp Function After completion of flight, memory is downloaded to obtain data and for the analysis of results. Temperature Not T Not 2 Reads the ADC value T

Flight Certification Testing  Upon the completion of the total payload, we will start flight certification testing. We will do both temperature and shock testing.  Temperature testing of the payload : We will place the payload in a ice chest which will contain dry ice and run the electronics as if in actual flight. We will place the payload in a ice chest which will contain dry ice and run the electronics as if in actual flight.   Shock Testing of the payload: To test the durability of the payload. We will drop the payload (about 10ft) to make sure the electronics are safely contained and will good conditions to take post-flight measurements. To test the durability of the payload. We will drop the payload (about 10ft) to make sure the electronics are safely contained and will good conditions to take post-flight measurements. We will analyze the data for both test and make the necessary changes needed for a successful flight mission.

Mission Operations *Synchronize our Real Time Clock with the Global Positioning System *Erase all test data before flight Launch Requirements *Synchronize RTC with GPS. *Computer to communicate with the Basic Stamp. Flight Requirements and Operations *Flight duration of approximately 4 hours *Reach approximately 100,000 before falling *Temperatures ranges from -60 to 85 degrees Celsius. *Ascent of balloon is expected to be smooth *Turbulence is expected during the fall. Data Acquisition and Analysis Plan Data to be collected: *Charge from solar cells *Product of current and voltage will allow us to compute the power output by each cell group. *Temperature inside the payload *Time stamp generated RTC *All data will be stored on board using EEPROM memory. Data needed: GPS system data: Longitude, Latitude, Altitude. This data will be gathered after the flight. The data will then be correlated to the data collected on the payload.

Organization and Responsibilities La Aces Program Office Team Leader (T. Joubert) Payload Design Data Analysis (L. Johnson) Project Management (T. Joubert) Mechanical Design (L. Sanford ) Documentation Thermal Design (M. Johnson) Electrical Design (S. McKinzie ) Software Design (T. Joubert ) System Design (K. James ) Calibrations Parts/BudgetFlight Data Analysis Scheduling (K. Hypolite) Results

Interface Control Electronic Interfaces (System) Need to know much voltage is coming in various components. Circuits needs to checked for connections to software and system components Thermal Interfaces Depends on the mechanical design for cooling of solar cells, temperature inside the box. All electronic components on the payload will need to endure extreme temperature changes Mechanical Interfaces Needs to be able supply an adequate amount of space for all components. Materials used in construction depend on thermal testing. To provide a suitable degree of impact resistance. System Design Needs to be able to communicate with all components. Interface Control Software Interfaces (Electronic) Needs to know when to read data; how often to read data.

Master Schedule ActivityStartFinish Mission Objectives/Project Management2/28/20053/9/2005 Payload Design3/2/20054/12/2005 Payload Development3/9/20054/12/2005 Payload Construction Plan3/9/2005 Master Budget/ PDR3/10/20053/13/2005 Submit Complete PDR3/17/2005 Preliminary Design Review3/18/2005 Spring Break3/21/20053/29/2005 Submit Complete CDR4/12/2005 Critical Design Review4/15/2005 Flight Readiness Review 5/23/20055/24/2005 Launch Trip5/22/20055/26/2005

Work Break Down Schedule  Time Schedule  Milestones

Budget NameVendorSourceDelivery Time QtyPart No.Price per quantity Price Solar CellsRadio ShackWent to store In Stock MultiplexerDigi-KeyTBD GlueTBD EEPROMDigi-KeyCatalog1 week1AT27BV JC-ND BatteriesRadioShackWent to Store In Stock14 AA FoamcoreACES Program In Stock1 ADCDigi-KeyCatalogTBD PopsicklesWal-MartTBD100TBD StandoffsDigi-KeyCatalog1 week101902ck-nd$ Construction Tools ACES Program In Stock Total So Far$21.55

RISK MANAGEMENT Levels of Risk HighMediumLow Transfer of Responsibility