1. BillikenSat-II The First Bio-Fuel Cell Test Platform in Space Senior Team Members: Darren Pais, Paul Lemon, Nathaniel Clark and Sonia Hernandez Faculty Advisors: Dr. Sanjay Jayaram, Dr. Krishnaswamy Ravindra and Dr. John George 4 communication windows per day (yellow) 4-7 minutes per communication window C&DH PIC 18 Micro- controller Power Battery Array Battery Chargers Solar Array 5V7V3.3V ADCS Thermal Control Experiment Experiment Communications Rate Gyro X Rate Gyro Y Rate Gyro Z Heater Thermal Sensor Control Switch Transceiver Power Amp Antenna Control Switch A/D Conv. Data Unregulated Bus 3V Bus 5V Bus 7V Bus Interface diagram of electrical subsystems Interface diagram for the entire satellite; this shows the interrelated nature of the BillikenSat-II subsystems Communication Window NmNm SmSm orbit Geo-Magnetic Lines of Force NmNm SmSm orbit Passive Attitude Control using Permanent Magnets and Hysteresis Dampers Dynamic Modeling of Permanent Magnet Stabilization, Both Undamped (blue) and Damped with Hysteresis Material (red) Enzymes V Anode Cathode H+H+ Nafion 112 H+H+ O2O2 H2OH2O e-e- e-e- Orbital ParametersDNEPR 07 Type of OrbitSun synchronous Inclination98 deg Eccentricity0.009 Altitude Perigee660 km Altitude Apogee772 km Period90 min Nylon & Nichrome for deployment Spiral etching Silver epoxy for contact Antenna: Nitinol shape memory alloy Antenna Deployment Nitinol shape memory alloy material is used in our antenna design. The shape memory effect means that the antenna can be restrained within the spiral etching pictured above until the satellite is deployed, and it will return to the straight perpendicular orientation once released. The antenna is restrained in the spiral by nylon line which is in contact with a nichrome wire. To deploy the antenna, a current is passed through the nichrome wire, which melts through the nylon line, thereby allowing the antenna to achive its straight orientation. Anode Membrane Electrode Assembly Cathode 4 cm Bio-Fuel Cell The payload of BillikenSat-II is an exciting new experiment developed by the Minteer Lab in the Department of Chemistry at SLU. The Minteer Lab works extensively on fuel cells that use biological fuels. The process by which electricity is produced is modeled in the diagram on the far left above. This energy alternative is especially suited for space applications due to its ability to adapt to use various biological fuels, such as dissolved food, orange juice or even astronaut waste. One of the difficulties with testing this technology in space is the size. The launch program chosen for this satellite is the Cubesat program, which limits the satellite to a 10 cm on edge cube with a mass of 1 kg. The center two pictures illustrate how the lab version was scaled down to meet the space and mass requirements. The diagram on the right here shows a more detailed computer model of the fuel cell used for our payload. Structural Temperature Range: -20 o C to 35 o C temperature sensor If T < 10 o C If T > 30 o C take no action turn on heater turn off heater true false true Heating/Cooling Cycle: Heater on ~ 14 minutes; Heater off ~ 18 hours Multi-Layer Insulation (MLI) Mylar Film Dacron Web Structures Engineering Besides the size and mass requirements, the Cubesat standard requires that each satellite undergo specific tests, mainly thermal-vaccum and vibrational testing. The structure of BillikenSat-II was engineered with these requirements in mind. Finite Element Analysis, along with analytic calculations, was used to ensure the deflections and stress caused by vibrations and gravitational loading during launch do not dammage the satellite. The structure is designed to be simple and convenient to integrate, with common fastners and interchangeable slots. Attitude Control Since the experiment aboard BillikenSat-II does not require any accurate pointing, the attitude control system is necessary only for communication purposes (the antenna must be quasi-parallel with the Earth’s surface). In order to limit the physical size and computational load, a completely passive stabilization method was chosen involving permanent magnets and hysteresis dampers. The figures below illustrate this method and demonstate the dynamic modeling. Orbital Analysis The Cubesat program uses a DNEPR launch vehicle which deploys satellites into near polar-circular orbit as seen below. Using the complete set of orbital elements, an STK © simulation was performed. A link analysis done using STK gives the communication window shown here over a 24-hour period, centered at the ground station in Oliver Hall at SLU. Thermal Engineering Our biological payload has a strict temperature survivable range of 4 o C to 40 o C. To maintain this temperature range, a combination of passive and active thermal control was used. The PEEK payload vessel, besides having good strength characteristics, also has extremely low thermal conductivity. Consequentially, the heat transfer from the main structure to the payload is negligible, which means the payload temperature is independent of sunlight or eclipse conditions. The passive control used is the Multi- Layer Insulation shown to the right. The active thermal control system uses a Thermofoil © resistance heater pictured below (43mm dia.) that is controlled via the logic loop shown. The bio-fuel cell will be maintained in a safe range of 10 o C to 30 o C. Systems Engineering One of the most challenging and rewarding facets of the BillikenSat-II project is its interdisciplinary nature. This project incorportates Electrical and Computer Engineering students and a Chemistry graduate student, with the Aerospace Engineering students. Integrating electrical and physical requirements is a considerable task, especially when they are driven, as this project is, by a biological payload at its core. Shown below are systems interface diagrams that illustrate the interdesciplinary nature of this project. Air Tight Fill Port Wire Interface Pressurized Payload Vessel Since the payload is a biological fuel cell, it is necessary to maintain the payload at near Earth-ambient conditions. The fuel cell is air- breathing, so it must be constrained within an oxygen tank. Besides the presence of oxygen, the fuel cell must also be kept at a pressure over 1 atm. A cylindrical design was chosen for the tank (red above) because it is nearly ideal in shape for a pressure vessel (a sphere being ideal, but not feasible in this size-limited environment). The vessel is made of PEEK polymer, which has a very high tensile strength, and incorparates a wire-interface to draw information from the cell experiment. Side Panel with Solar Cells Antenna 3-view & isometric Assembled Hardware Main Structure CD&H Power Comm Battery Box Payload Thermocouple Active Thermal Control Antenna Housing Antennas Kill Switch Remove before flight pin Solar Panels Copper Coated PCB board Magnets Hysteresis Rods Structures ADCS Power Comm. C&DH Thermal Legend