Wireless System for TPS SensorsPresented 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 SpecsTransmission Type Radio Frequency

Data Rate 4 Hz

Data Transfer Real Time

Power Source 2 AA

System Life Power 8 days constant transmission

Temperature Resolution +/- 1% readout

Temperature Range 0 – 1128 degrees Celsius

Transmitter Size 3 ¼” x 2 ¾” x ¾”

Weight 3.2 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

% Error for Range of Temperatures

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 500 1000 1500 2000

Temperature (F)

% E

rro

r

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