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Aerospace Engineering Faculty

Space Systems EngineeringComputer Engineering Laboratory

Feb. 11, 2009

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Intra-Spacecraft Wireless

Sensor/Actuators Network

Rouzbeh Amini

Promoter:Prof. Eberhard Gill (LR)Daily supervisor:Georgi Gaydadjiev (EWI)

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Aerospace Engineering Faculty &Computer Engineering Laboratory

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Contents

1. Project Objectives2. Wireless on-board communication

3. Power management

a. Simulation environment

b. Attitude determination

c. Power management

4. Conclusion

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Project objectives

i. Determining useful COTS wireless standards foronboard communication

Evaluating WiFi, Zigbee and Bluetooth as three potential

candidates (COTS standards)ii. Design a system level power managemer for a set of

Attitude Determination and Control System sensorsand actuators onboard spacecraft and evaluate theenergy efficiency of the system and functionality for agiven operation scenario.

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Part I

Wireless on-board

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Motivation

Wired CDHS designs [1]:

Wires/connectors failure

Costly late design change

Development time overhead Undesired ground loops

EMC and crosstalk

Test/integration difficulties

Limited design flexibility

Mass overhead of cables/wires (6-10 %)

Final installation of Spacecraft harness atLockheed Martin

[1] Amini, R., et al.., "New generations of spacecraft data handling systems: Less Harness , More Reliability", In the Proceedings of IAC06, 2006

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Wireless on-board

Fly-by-wireless plane (AIVA) developed in Portugal(2m Long 4m Wingspan 25kg)

1- Practically, not every subsystem canenjoy a wireless communication link2- Power management plays a great role in increasing autonomy

Possibilities:

1. Developing a new standard2. COTS standards, e.g., WiFi, Zigbee and Bluetooth

In both cases the following issues should be evaluatedfor each subsystem:

Communication bandwidth Computational overhead

Data integrity and fault tolerance

Volume, mass and power usage overhead

Power management and autonomy

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Wireless Standard selection

Onboard data traffic can be categorized to:

1. Payload data2. House-keeping data3. ADCS data

The different data traffic types impose various requirements on the data handlingsystem:

1. Data rate2. Data robustness3. Fault tolerance4. Reconfigurability

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WiFi is more suitable for long range and high data rate communication

Bluetooth and ZigBee are low power and low data rate standards

ZigBee is more flexible and configurable Bluetooth supports a higher data rate and consumes more power [2]

Comparison of standards

[2] Amini, R., Gaydadjiev, G, Gill, E., "The Challenges of Intra-Spacecraft Wireless Data Interfacing", In the Proceedings of IAC07, India 2007

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Onboard Wireless Sensors/ActuatorsNetwork (OWSAN)

Wireless Sensor Network Wireless Ad-hoc Network OWSAN

Number of nodes >100 (1000s) 10-100

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Part II

Power Management

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Power Management

Goal to achieve: Maximizing power usage efficiency of Attitude

Determination System (ADS) of a microsatellite in a realisticscenario

Three scenarios are designed:

1- Pointing mode: the spacecraft points to a certain location on Earth for ashort period of time. High accuracy requirements (< 1deg)

2- Tracking mode: the spacecraft tracks the ground station. The accuracydemand is lower than the pointing mode. Medium accuracy requirements(< 3deg)

3- Spacecraft stabilization: the spacecraft is only stabilized to perform thescience mission. Low accuracy requirements(< 10deg)

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ADS accuracy defines: Type of employed sensors energy consumption

Sampling frequency data rate energy consumption

Onboard computation load energy consumption

Following sensors are selected:

3-axis magnetometer

3-axis Gyroscope

6 sunsensors

Simulation Environment

Matlab/Simulink

- Environment simulation- Spacecraft simulation

- Attitude determination tools- Power manager

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Simulation environment

Case study: BIRD satellite

Dimension: 620x550x620mmWeight: 92kg

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Following models are build and tested:

Orbit propagator (SGP4)

Ephemeris (Sun, Earth, Eclipse)

Magnetic field model (IGRF) Spacecraft dynamics and kinematics

External disturbances (radiation and gravity)

Deterministic determination algorithms

Kalman filter determination algorithms

Determination is quaternion based

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Power managementPossible power management schemes:

i. Simple and decentralized approach:

Sensor node may turn off its transmitter after transmitting amessage and go to idle mode. Sensor goes to idle modewhen not enough power is available

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ii. Dynamic centralized approach Changes the sensing

accuracy to reduce data rate

Changes the durationof the idle/on/off time

Uses an algorithm to

estimate the sensor's data

Decides which set ofsensors should be used touse the least power toachieve the acceptable accuracy

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iii. Dynamic de-centralized: Similar to centralized approachbut the decision making is put on the sensors side.Sensors should communicate and find the best solution

Neural network decision making (Training andlearning)

Fuzzy logic decision making

Seems to be suitable for space apps due tocalm and predictable nature of space and ADS

in our case. Etc.

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Conclusion

Examining more Eclipse scenarios to improve the ADS and tune it

Examining different scenarios of absence of sensor measurements

Examining Unscented filters for ADS

Designing predictive power management schemes to maintain theperformance

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0211_Rouzbeh