Space Engineering Institute (SEI) Space Based Solar Power Space Engineering Research Center Texas Engineering Experiment Station, Texas A&M University By: Bryan Babbitt, Nate Broughton, Will Dixon, Stephanie Hasskarl, Travis LaCour, Veronica Medrano, Joseph Noska, and Mindy Watts NASA Mentor: Dr. G. D. Arndt TAMU Mentor: Dr. Frank Little

Project Goal Develop a design for a sandwich solar power satellite module with retrodirective wireless power transmission system for inclusion in Japanese LEO to earth solar power satellite demonstration Demonstrate software-controlled retrodirective wireless power transmission system

Module System Sandwich Design Antenna Array Photovoltaic Cells Energy Storage & Power Conversion Retrodirective Control logic Thermal Management

Fall 2009 Goals Perform case studies for the preliminary design concept with software tools such as Satellite Tool Kit and Thermal Desktop Determine hardware components for: – Solar energy collection – Power system – Transmission system – Antenna

STK / Photovoltaic Cells Chose 35° angle of inclination circular orbit, based on orbits of other Japanese satellites of similar size. Chose a single crystal Si photovoltaic cell that has an efficiency of 17% We modeled the top surface of our satellite ( 1 m^2) at this orbit and found: – Found that the average energy acquired for every month is 126X10^6 Joules — ~3X10^6 Joules per test transmission Determined experiment dates and times for beaming to College Station – Satellite passes within 45° of normal – Maximum transmission length of 170 seconds – Eclipse requirement limits transmission times, but is still feasible.

STK Image of Reception Cones

Power Transmission and Antenna Power Transmission – Determined a 40 km reception area required to achieve a beam coupling efficiency of 90% – Estimated a transmitting power of 2kW necessary for minimum ground pattern detection signal of 0.1nW – Identified hardware components for transmitter subsytem Microstrip Patch Antenna – Maximum 450 element phased array – Capable of achieving 2kW transmitting power – Required area of elements is small enough to fit in the allowable area of 3/4 m^2 without the possibility of inducing side lobes – Polarization and power handling capability meets SPS requirements – Inexpensive and uncomplicated to manufacture

Transmitting Antenna Corporate Feeding Employs uniform amplification and phase shift to a 3x3 element subarray 5880 Duroid Substrate and copper rectangular patches

Silicon Solar Array Saft MPS Li-ion Battery Misc. Components of Retro Directive Control and Housekeeping Power Transmission System (Solid State Amplifiers) Terma Array Power Regulation Module Terma Battery C/D Regulation Module IRF E-Series DC-DC Converter 28V Bus Satellite Bus and Electronics The Saft MPS battery has a nominal energy of 480 Wh and an end of charge voltage of 32.8 V DC-DC Converter, Regulation modules and battery have an efficiency of over 90% Less than 6 Kg. for DC-DC Converter, Regulation modules and battery

Thermal Management Goal is to ensure that equipment is kept within designated temperature ranges (-20°C to 60°) Hot Case: Transmitting produces about 3 kW of heat – Plan to transmit during eclipse – Use loop heat pipes to transfer heat to radiator on bottom of satellite – Use thermal storage with phase change material Cold Case: Shaded by earth and not transmitting – Use thermal energy stored from transmission time to heat electronics – Use resistance heaters if additional heat is needed

Thermal Desktop Image

Transient Temperature Response Heating of electronics during transmission with assumed mass of 20 kg and assumed radiator size of 0.25 m 2. Cooling of electronics after transmission, with assumed mass of 20 kg and assumed radiator size of 0.25m 2.

Retrodirective System Hardware Retrodirective Control Method – Researched control technique that uses a 2 nd harmonic transceiver to double and conjugate received pilot beam – Requires that a receiving antenna be nested within the transmitting antenna array – Requires a pilot signal of 2.9 GHz Software Retrodirective Control Method – Use logic to establish conjugate phase of received pilot signal – Use logic to implement phase conjugation and redirect transmit beam in the direction of the received pilot signal. – Preliminary design and required components have been identified – Method requires same antenna configuration as hardware method – Frequencies of pilot signal less limited

Retrodirective System

Summary Determined solar energy data for a 35° inclination orbit Determined power level of 2 kW required for transmitting detectable signal Plan to transmit during eclipse to meet thermal requirements Selected hardware components that meet power requirements Developed design of electronics hardware Developed preliminary design of satellite, but final design is to be determined with further analysis Gained knowledge of Thermal Desktop and can model accurately thermal behavior of satellite when it is updated.

Plan for Spring 2010 Integrate systems into a unified design Conduct trade studies for different system configurations. Maximize photovoltaic and antenna area while allowing sufficient space for radiators. Perform test demonstration of retrodirective system