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Design of Thermal Control Sub-System(TCS)

Picosat course

May 18, 2006

IAA,National Cheng Kung University, Tainan

J. H. Chou

Department of Engineering Science

National Cheng Kung University

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OutlineI. Review of TCS key concepts

II. Design considerations

III. YamSat thermal design

IV. Summary

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I. Review. Why do we need TCS for PicoSat?

. Working Temperature: sensors, electronics

and materials

. Temperature uniformity: thermal stress

. PicoSat environment: cold and near vacuum

. Energy source and sink

. Thermal balance and heat transfer path

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Picosat thermal environments

. Three phases:

.launch

.mission lifetime

.reentry self-destruction

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Key issues:

. Environment

. Components temperature specification

. Heat source

. Heat sink

. Heat transfer path and mechanisms

. Control techniques

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Typical temperature range for selected satellite components

Components Typical temperature range, ℃

Batteries 5 to 20

Electronics 0 to 40

Infrared detectors - 200 to – 80

On-board computer - 10 to 50

Propellant, hydrazine 7 to 35

Solar arrays - 100 to 100

Structures - 45 to 65

 

Note: reference only. Check manufacturer’s data for details.

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Requirements

-Temperature Limits

-Survivability

Thermophysical Property Values

Electrical Power Dissipation

Spacecraft Geometry

Spacecraft Orientation and Attitude

Radiation Property Values

Comparison

Predicted Thermal Performance

Thermal Analyzer Computer Program

(Thermal Math Model)

Thermal Control Hardware Elements

Radiation Computer Program

(Geometric Math Model)

System-Level Tests

Component-Level Tests

Radiation Absorbed on

Exterior Surface

Radiation Exchange Factors and View Factors

II. TCS design considerations

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Some heat sources:

. Solar and planetary radiation

. Planetary reflection

. Equipment heat sources: electronic devices

batteries

propulsion

. Reentry atmospheric frictional heating

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P

Earth

Mean value of Direct Solar Flux 1385+5 W/m2

Gs

Emitted Radiation

Earth Infrared 237+21 W/m2

Albedo (30+5)% of Direct Solar, a

q1

Low-Earth Orbit Spacecraft

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Typical heat sinks:

. Satellite space environment (ultimate):

cold and near vacuum condition

. Equipment heat sink (intermediate):

special designed

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Basic heat transfer path and mechanism:

. Solid material: conduction

. Space: radiation

. Atmospheric air: convection (launch &

reentry)

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Available thermal control techniques:

passive control vs active control

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0.25 mil Mylar + 0.001mil aluminized surface

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212 )1(

cos

HF

]

1

21[

2

1 2

12 H

HHF

RhH /

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Qloss = Qabs,ex + Qabs,in

Qe= Qa

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Tokyo Institute of Technology

"CUTE" (CUbical Titech Engineering satellite) •Size : 10 cm x10 cm x10 cm &Weight : 1 kg •COTS(Commercial off-the-shelf) components

.Sun-synchronous polar orbit, Height 650km

Thermal analysis by ANSYS finite element method package with space temperature of 3K

Estimate the max temperature is about 80 Celsius degree, and the mininum temperature is -40 Celsius degree

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Aalborg University, Denmark

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23/47Taken from AAU

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III. YamSat thermal design, NSPO

. New generation of sensors (payload)

.Smaller

. Cheaper

. Faster

. Better

. 10 cm3 x 1 Kg

. Internal space & power limited

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. Mission life duration: 1 month

. Altitude: 650 Km

. Orbit period: 16267 hours

. Power: GaAs and Si solar cells

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YamSat

Thermal Management: passive control, black painting inside the satellite

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The YamSat TCS ensures the proper thermal environment for YamSat and thermal interface control with the instruments.

Component Thermal Control

The TCS shall provide thermal control for all thermally sensitive YamSat components.

Thermal Passive Control

The thermal control shall be achieved through passive elements, as thermal blankets, insulation, and surface finishes.

Thermal Margins

For all components, an uncertainty margin of 5°C shall be included in all cases so that the maximum or minimum expected flight temperature can be determined.

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Selection of Thermal Control Materials

. Materials with low-outgassing characteristics to avoid the contamination of other spacecraft equipment.

. All electrically conductive layers of thermal finishes shall be grounded to the vehicle structure.

. Thermal finishes and materials with low degradations in solar absorptance.

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衛星軌道環境

Solar constant (W/m2)

Earth radiation(W/m2)

Albedo coefficient

Cold case

1321.0 275.0 0.35

Hot case 1423.0 201.0 0.25

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Direct Incident Solar Solar Constant1423 W/m2 (Hot Case)1321 W/m2 (Cold Case)

Earth IR275 W/m2 (Hot Case)201 W/m2 (Cold Case)

AlbedoAlbedo Coefficient0.35 (Hot Case)0.25 (Cold Case)

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元件 Tmin （ﾟC ）

Tmax （ﾟC ）

電池（充電） 0 45

電池（放電） -20 60

CPU -40 85

Micro-spectrometer

-20 40

Magnetometer -40 85

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. Structure: 7075 T6 Al Plate.Surface properties. Isolators

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Significant conduction heat loss from components to structure panels and may cause some unit temperatures, especially the battery, lower than their allowable temperature limits.

Thermal isolators were used for screws that fix components to structure panels to avoid substantial conduction heat loss.

An appropriate combination of surface properties of outer and inner sides of structure panels to maintain component temperatures within their ranges.

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Component

Structure Panel

Isolator

Isolator

Application of thermal isolator

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Qualification margin

Acceptance margin

Uncertainties

Predicted

temperature

range

Uncertainties

Acceptance margin

Qualification margin

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. Satellite environments

. Heating by sun and power dissipation

Worse hot and cold conditions

. COTS components vs ASIC

. Scale down vs New design

. Modular approach

. Passive thermal control:

Thermal isolators

Surface finishes/paints

Controlled duty cycles to manage power dissipation

. Reentry self destruction by atmospheric heating

VI. Summary

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TCS design home work:

1. Specify your PicoSat’s missoin thermal environment

2. Following the analysis of AAU, estimate your PicoSat’s maximum and minimum temperature

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References

1.Fortescue, P. W. and Stark, J. P. W. (eds.), Spacecraft Systems Engineering, 2nd edition, Chapter 8.5 and Chapter 12, John Wiley and Sons, 1994

2.Gilmore, D. G. (ed.), Satellite Thermal Control Handbook, The Aerospace Corporation Press, 1994

3.Larson, W. J. and Wertz, J. R. (eds.), Space Mission Analysis and Design, Chapter 11.5, Microcosm, Inc. and Kluwer Academic Publishers, 1992

4.Any basic heat transfer book for undergraduates

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5.Holmes, W. C., et al., TU Sat 1: A novel communication and scientific satellite, 16th AIAA/USU Conference on Small Satellites, 2002

6.Schaffner, J. A., The electronic system design, analysis, integration and construction of the Cal Poly State University CP1 CubeSat, 16th AIAA/USU Conference on Small Satellites, 2002 7.Tsai J-R, “Thermal Analytical Formulations in Various satellite Development Stages”, 8th AIAA/ASME Joint Thermophysics and Heat Transfer Conference, St. Louis, Missouri, USA, June 2002.8.Tsai J-R, “Satellite Thermal System Verification - Thermal Balance Test and Thermal Vacuum Test”, 4th pacific International Conference on Aerospace Science and Technology, Kaoshiung, Taiwan, May 2001.