Wireless System for TPS Sensors Presented By: Tye Reid and Greg Swanson

Outline Introduction Motivation Project Challenges Prototype Prototype Specs Calibration Testing Results Conclusion

Introduction Goal – to design and build a wireless system to transmit data gathered from sensors embedded into the TPS of atmospheric entry probes. Thermal Protection System (TPS) Forward Bay Cover Backshell Pressure Vessel

Motivation Reduction in Complexity (eliminates harnesses, wire routes, and wire holders) Easier and Safer Implementation (routing through safety barriers isn’t needed) Improved assembly efficiency Weight Savings

Project Challenges Transmission through RF non- transparent material Transmission through high interference environment Thermal protection of wires and circuits Size requirements associated with space flight

Prototype Zigbee RF transmitters chosen for their low power/bandwidth design Thermocouple voltage to temperature conversion chips for embedded thermocouple sensor readings Optimized PCB layout to minimize EMI Different antennas for signal strength testing

Prototype Specs Transmission TypeRadio Frequency Data Rate4 Hz Data TransferReal Time Power Source2 AA System Life Power8 days constant transmission Temperature Resolution+/- 1% readout Temperature Range0 – 1128 degrees Celsius Transmitter Size3 ¼” x 2 ¾” x ¾” Weight3.2 oz

Calibration +/- 1.2% Temperature Error Error sources –Thermocouple voltage to temperature conversion chip has a +/- 3 degree C error –Program rounds off decimals and converts to degrees F –Thermal Differences between the thermocouple to circuit connection and conversion Chip

Testing X-Jet at NASA Ames –Testing for transmission out of x-jet chamber –Antenna testing –Distance tests –Precision and Accuracy tests

Results Clear transmissions out of test environment Temperature data matched rough analytical analysis Repeatable Data Small PCB antenna worked just as well as larger antenna

Conclusions Zigbee RF technology demonstrates a solution to wiring problems Integrated sleep mode design would allow for 8 years of operation off of 2 AA batteries Initial prototype weighs 0.2 lb reducing sensor system weight by 50% Miniaturization and further development is recommended Next step will be to implement sensors on a probe flight such as the RISE program balloon