Solar Cell EfficiencyFlight Readiness Review Teddy Bounds Angela Dunn Joel Sasser
Design Constraints Payload weight: 450 g Payload dimensions: 20cm x 20cm x 8cm Payload includes two holes that pass through the width of the payload for vehicle interface.
Component Mounting Internal components are mounted with screws, washers, and nuts to the cardboard on the exterior of the payload. Solar cells are attached to a piece of foam core with polyurethane adhesive and the foam core is mounted with screws, washers, and nuts to the cardboard on the exterior of the payload.
Thermal Control ¾ inch foam insulation is used for the exterior walls of the payload to reduce heat loss through conduction. Reflective tape is attached to the exterior of the insulation to reduce heat absorbed through radiation.
Thermal Testing The expected temperature range of the payload exterior is 0 – 100 degrees C because of the large amount of heat dissipated from the solar cells. The finished payload was placed in dry ice for 1.5 hours and remained operational throughout. The payload material was placed in a furnace at 125 degrees for 1 hour and was undamaged. Above: Thermal tests (5/3/07)
Strength Dove tail joints were used to increase contact surface area and thus increase the strength of the payload. Cardboard was added to the surfaces where components were mounted to prevent mounting hardware from damaging the foam insulation.
Structural Testing An Impact test was done from 30ft on the payload prior to mounting the solar cells and remained intact.
Pre-Flight Checklist • Open Compartment, inspect all connections on the interior and exterior of the box. Inspect that the solar cells and pyranometer are properly attached. • Connect all batteries and connect Balloon-Sat to computer via parallel port. Verify that exterior switch is in “on” position. • Run Pre-Flight program to zero all vales within the memory. Run flight program and observe whether all readings are in agreement with expected values (no zeros or maxed values and temperatures showing room temp.).
Pre-Flight Checklist • If any readings are different from expected values, troubleshoot and fix faulty connection. Repeat steps 2 and 3 until all readings are reporting correct values. 5) Reload Pre-Flight program to clear memory. Reload Flight program and switch payload off. Disconnect parallel port cable. • Inspect all interior connections again and close the box. Inspect all exterior connections. Payload is ready to be attached to the balloon. • Just prior to attaching payload to balloon, switch the power on. If possible, check that the switch is still in the “on” position just prior to launch.
Post-Flight Checklist • Upon retrieval of payload, switch power off. • Once ready for data retrieval, open Basic Stamp Editor with Post-Flight program ready, connect the payload to the computer, and switch on the power. Run post flight program within a 5 min time frame. • Turn off power, close Basic Stamp Editor, and open Term232 program. Select “save retrieved text to file.” • Turn power back on. Data should automatically import into saved file. • Import saved file into MS Excel, using spaces to set column boundaries.
Data Analysis • Temperature measured inside the box and from the thermistors on the pyranometer and cells • Time recorded, followed by a series of voltage readings as resistance varies. • Data stored to EEPROM and output to excel for analysis • Max power output at each interval calculated, as well as internal resistance • Efficiency at varying altitudes, temperatures, and pressures calculated Top Right: Expert data analysts (5/2/07) Bottom Right: Retrieving data from payload (5/2/07)