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衛星結構設計衛星結構設計 (II)(II)

祝飛鴻

6/17/2004

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What you should learn from this course?

低軌道小衛星發展趨勢 Why spacecraft structure fails?

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What you should learn from this course? Concept of System Engineering

Concept of Development Process

You may not have the opportunity to learn

from other courses.

These 2 concepts can be applied to any field

and will be extremely useful when you are

in a management role or decision making

position.

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Concept of System Engineering: Each system can be logically or functionally break into subsystems.

Each subsystem is not a stand alone item but interface with each

other by some means.

Best subsystem design will not lead to a best system. In some

cases, best subsystem could lead to an unworkable system.

Iterative compromise between subsystems is unavoidable in

achieving a workable system design.

A good system engineer must know the inter-relationship between

subsystems and relative importance of each key parameter.

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StructureSubsystem

EPS

• Type of solar array.• Size• Weight• Area

TT&C

C&DH

TCS

ADCS

RCS

• Radiation area• Thermal conductivity

• Tank size• Thruster alignment

• Size• Weight• Type of antenna• Field of view

• Size• Weight• Field of view• Alignment

• Weight• Size

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Concept of Design Process: Materialize the flow and steps necessary to complete the task.

Mission Orbit

Candidate LV

Target Weight

Fairing Size

System & SubsystemDesign Concept

Hardware Selection

Hardware Size

Orientation & FOVRequirement

StructureConfiguration

MechanicalLayout

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Target Weight

Candidate LV

Weight Allocation

HeritageData

Design Concept

SystemDesign

Weight Estimation

Weight Re-allocation

PreliminaryDesign

WeightCalculation

DetailDesign

WeightReduction

FinalWeight

ActualWeight

Actual HW

Over Weight

?

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低軌道小衛星發展趨勢

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Ref. 1: JPL Technology for Small Space Missions, Les Deutsch, March 29 2001

JPL Development Trend (Ref. 1)

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Formation Fly

Paradigm Shift- same mission with lighter and smaller satellite -

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Single Large Spacecraft Single Small Spacecraft

Limited by

physical law

and state-of-

the-art technology

Virtual Satellite Technology Breakthrough

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Satellite Design: Past, Present, and Future, Cyrus D. Jilla,

International Journal of small satellite Engineering, 1997. The Present:

Conventional subsystem by subsystem design

Modular design for multiple missions

Small satellite: low cost high risk design

The Future:

Multifunctional structures

Nanotechnology & MEMS systems

Distributed satellite system

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Solar Array- Specific Power

Current technology: ~200W/Kg.

Future goal: ~300W/Kg

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Li-ion

130Wh/Kg

Battery- Specific Energy

Thin-film lithium battery

300Wh/Kg

NiH2

25-40Wh/Kg

NiCd

25-30Wh/Kg

Rechargeable lithium batteries sees as future. (Ref. 2)

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ADCS: (Ref. 2)

Compact, light weight sensors and components.

Integration of components (GPS & Attitude Sensors)

Complete spacecraft autonomy

Sun Sensor

Star Tracker

Gyro

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Why spacecraft structure fails?

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Un-execusive Event

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Unforeseen Event

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Unfortunate Event

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Unlucky Event

Design Loads vs Coupled Loads Results

Random Vibration Loads

Shock loads

Load Source

Response Prediction

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Unforgivable Event

Design to failure

Analysis oversight

Over testing