% 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

Test # 8 & 5, Test For Repeating Data

0

50

100

150

200

250

0.3

50.7

100

135

272

193

315

352

474

494

515

551

600

635

656

691

784

Seconds

Te

mp

era

ture

(°C

)

0.6

0.2

0.4

0.8

Test 5, Depth 0.6

Test 5, Depth, 0.2

Test 5, Depth 0.4

Test 5, Depth 0.8

Calibration and Test 2

0

50

100

150

200

250

0.03

7.63

15.2

22.8

30.4 38 46

53.5

61.1

69.2

76.8

84.5

92.1

99.6

107

115

122

130

138

145

Time (s)

Te

mp

atu

re(˚

C)

0.6

Box

0.4

0.8

Goals

Acknowledgements

Design ConsiderationsPrototype Design

Testing

Results

Joe Law- Faculty AdvisorDavid Atkinson- Faculty AdvisorAustin Howard- Graduate AdvisorJustin Schlee- Student AssociateRaj Venkatapathy- NASA ClientDavid Hash- NASA ClientJohnny Fu- NASA / Sierra Lobo

Motivation

Calibration

X-Jet The inclusion of thermal protection system (TPS) sensors into a spacecraft’s TPS material allows for the measurement of different aerothermal and aerodynamic properties in-flight.  However, the presence of sensor wiring can add complexity to the system due to the process of routing wires in the spacecraft and the difficulty of jettisoning the heat shield after entry.   Many current and past spacecraft engineers have decided not to fly embedded sensors in an effort to mitigate the risk of spacecraft failure during entry.  A wireless instrumentation system could collect the required measurements needed for scientists and engineers to improve future spacecraft design while lowering the overall risk in upcoming entry vehicles.  In addition, a wireless sensor system can be easier to install compared to a wired system, thus making the inclusion of TPS sensors easier to accommodate during spacecraft assembly.

• Design a wireless system using off-the-shelf components

• Research present wireless technologies and choose specific components

• Characterize the system and how it responds to environmental noise

• Implement thermocouples in a TPS material and test at NASA Ames’ X-Jet

PCB Layout

Actual Prototype

Schematic

-Plasma Torch in side a vacuum chamber to simulate atmospheric entry

-Plasma torch can reach heat flux of 1000 W/cm^2

-Used for initial TPS senor validation and testing

-X-Jet is located at NASA Ames Research Center

Transmission Testing

-The above plot is from when the initial transient of the X-Jet ignition caused interference disrupting transmission

-The graph shows that transmission was recovered in the range of 2.2 sec

-The above percent error was calculated using the type K thermocouple voltage-temperature table

-The prototype was given a precise voltage at the thermocouple input and then compared the expected temperature from the table

-the above graph represents two separate X-Jet tests with exactly the same testing parameters

-from the recorded temperatures you can see that each test was almost identical

-Data shows secondary heating during calibration test of thermocouples closest plasma torch

-from the graph it can be interpreted that the 0.8” depth thermocouple was malfunctioning, but other three were unaffected

Future Work

Introduction

•Size Reduction of Wireless System

•Mesh Networking of Wireless System

•Transmission through a pressurized crew compartment

•Incorporating data storage

•Determine signal to noise ratio

•Programming Wireless hardware with sleep mode

•Characterize hardware time to recover signal

Initial testing followed pre-determined procedure to test for susceptibility to interference using different antennas and power levels to verify data results. Testing was conducted using LI-900 shuttle tile with thermocouples embedded at four different radial depths. The thermocouples were then connected to the prototype for all X-Jet testing. Below are the graphs of various tests that we conducted.

First three types of wireless links were evaluated, Radio Frequency, Near-Field Magnetics, and Infrared light. Radio frequency was chosen because there was no line of sight for infrared, and near-field magnetics is an undeveloped technology. A comparison between current wireless standards was done, and can be seen in the comparison table. Zigbee became the best choice for the wireless solution because of its low-power and mesh networking properties.

•From calibration of the circuit it was found that temperature data was accurate to ±1% of the reading temperature.•From the X-Jet testing, it was found that the wireless link using the Zigbee protocol was strong and therefore a very feasible solution to the wired sensor problem.•Temperature data in repeated experiments lead to repeatable data, this data, plus the fact that electromagnetic noise is unpredictable, enforces the idea that the transmission was unaffected by noise.•The circuit was found to be able to recover from noise interferences and resume regular transmission of data within 2.2 seconds. •Further development into implementing Zigbee technology into sensor data collection on future probes is recommended.

ZigBee 802.11 Bluetooth UWB (Ultra Wide Band

Wireless USB

IR Wireless

Data Rate 20, 40, and 250 Kbits/s

11 and 54 Mbits/sec

1 Mbits/s 100-500 Mbits/s

62.5 Kbits/s 20-40 Kbits/s

115 Kbits/s

Range 10-100 meters 50-100 meters

10 meters <10 meters 10 meters <10 meters (line of sight)

Networking Topology

Ad-hoc, peer to peer, star, or mesh

Point to hub

Ad-hoc, very small networks

Point to Point

Point to Point

Point to Point

Operating Frequency

900-928 MHz (NA), 2,4 GHz

2.4 and 5 GHz

2.4 GHz 3.1-10.6 GHz 2.4 GHz 800-900 nm

Complexity Low High High Medium Low Low

Power Consumption

Very Low

(Low power is a design goal)

High Medium Low Low Low

Repeatability

• Mass reduction and space savings provided by wireless sensor system

• Heat shield jettison can be accomplished without having to sever sensor wires

• Reduction of complexity in installation of embedded sensors

• Greater flexibility in placement of sensors

• A wireless system reduces wire routing holes increasing structural integrity

Time Data Was Interfered With

Se

c

0.6

75

1.3

5

2.0

25

2.7

3.3

75

4.0

5

4.7

25

5.4

6.0

75

6.7

5

7.4

25

8.1

8.7

75

9.4

5

10

.12

10

.8

Interference

LI-900 Layout

LI-900

Prototype and TPS used in X-Jet Testing. Prototype is located in ThermaSense box.