LionSat - Power Subsystem Team

 

nLocal Ionosphere Satellite

nScientific goals

nEngineering goal

nEducational goals

 

Introduction

We were tasked with working on the power subsystem of the LionSat.  Being the first group tasked with this problem, we focused on a high level design which will help future groups.  We also worked out the optimum method and pattern for solar cell layout on LionSat.

Another project we worked on was the BalloonSat component.  The balloon satellite is a data collection module that will be tethered to a weather balloon.  The BalloonSat project will provide critical technical data concerning the output characteristics of space rated solar cells operating in a high earth atmosphere environment.  The module will gather current, voltage, and temperature data from different attitudes with respect to the direct rays of the sun.  This information will be critical for designing our peak power tracking module and knowing how our solar cells will operate.

Design Procedure

           Our research will focus on the output characteristics of space rated solar panels.  Since, the LionSat will be spinning while in orbit, the angle of each solar cell with respect to the sun will continuously change.  Therefore, we need to know what angle the solar cell is with respect to the sun while the BalloonSat module measures the voltage and current output of the solar cell.

We have designed a fly’s-eye solar panel instrument to simultaneously record the angle of incidence of the rays of the sun and the voltage/current measurements.  The fly’s-eye employ’s eight photoconductors mounted around a single solar cell which will be attached to the outside of the test box.  The angle of incident can be determined by viewing which photoconductors are conducting and the current intensity.  The output characteristics of solar cells vary with temperature and the solar arrays on the LionSat will be exposed to the differing temperatures to the Earth’s upper atmosphere.  So, we included a temperature sensor in our design to measure the effects of the environmental temperature. 

A Basic Stamp II microcontroller will act as the data collection device for BalloonSat.  The Basic Stamp II will interface with all other BalloonSat components through serial input/output communication.  We also included an EEPROM in the design for data storage.  One ADC will be located between the Basic Stamp II and the fly’s-eye and the other will act as a voltmeter for the solar cell.

The BalloonSat test box will be made of plastic.  Circuits within the box will be connected to the fly’s eye through holes punched in the end of the box.  Foam rubber will cushion the circuitry in the event that the module becomes detached from the lanyard.

The circuit is designed around a Radio Shack solar cell.  A space rated Si solar cell will be used for the actual BalloonSat flight.  This will provide data closer to values needed to design the LionSat power distribution network.

The single largest advantage of our design is that it utilizes an actual space rated solar cell.  Another advantage comes from our consideration of the angle of incidence that the rays of the sun has with the solar cell.  The fly’s-eye will allow us to calculate this angle.  We also took into account the differing performance of the solar cell at different temperatures.  So, we included a thermo-sensor in the module that will take readings simultaneously with the voltmeter/ammeter.  Our design takes into account the temperature and illumination variables that the solar cells will encounter in space.  Another advantage of our design is the low cost.  We acquired most of our parts for free, either from Dallas Semiconductor Inc. or the PSU EE stock room.  The Basic Stamp II and prototype board cost $101.15.  The whole BalloonSat design accounts for less than %20 of the LionSat total semester budget ($600).