HokieSat Thermal System

Michael BelcherThermal Lead

December 11, 2002

Introduction

• Thermal modeling

• Software

• Calculations

• Results from analysis

• Conclusions

• Future plans

Heat Transfer Fundamentals

• Convection• Q = hconvectionA(T)

• Conduction• Q = G(T)

• Radiation• Q = A (T2

4-T14)

• Heat transfer in space occurs through conduction and radiation only

Thermal Model

• Predicts temperatures of spacecraft components

• Identifies problem areas

• Useful in analyzing existing design

• Usually software based• TSS, SINDA, TRAYSIS, SSPTA, I-DEAS

SSPTA

• Simplified Space Payload Thermal Analyzer

• Evaluation/ Educational Software from Swales Aerospace

• Consists of several smaller programs, which calculate view factors, radiation couplings, absorbed heat loads

• Used in conjunction with SINDA

SINDA

• Systems Integrated Numerical Differential Analyzer

• Freeware

• Calculates temperatures based on a network of thermal nodes

• Solves network using finite difference method

SSPTA Models

SSPTA Models

SSPTA Models

Radiation Surface Properties

Irridite Aluminum 0.01 0.11

300 Series Stainless Steel 0.47 0.14

Delrin AF 0.96 0.87

GaInP2/GaAs/Ge (Solar Cells) 0.92 0.85

Ultem 2300 (PPTs) 0.3 0.3

Conduction Couplings

• Calculated in Excel

• Q = G(T)

• G = hA

• Value of h dependant upon:• Interface type• Conduction coefficient

Conduction Couplings

h (W/m2°C)

Interface type Low High

Bolted 300 1000

Pressure contact 15 30

Thermal interface filler 10,000 15,000

Thermal Models

• Created separately for independent verification and ease of use

• Stand-alone models• Battery box• CEE• External

• Integrated model• Internal, external, battery box, CEE

Hot and Cold Case Parameters

Hot Cold

Peak powerrequirements

Average powerrequirements

Maximum orbitalincident fluxes

Minimum orbitalincident fluxes

Model Results: CEE

• Preliminary results showed need for a thermal filler around bolted interfaces

Component

Min Ave Max Cold Hot

Boards 35.2 38.3 46.6 -40 80

Cells 30.0 30.0 30.2 -40 80

Predicted Temps (°C) Operational Limits

Overall Model: Cold Case

Component

Min Ave Max Cold Hot

Batteries 43.2 43.8 44.6 5 20

Boards 20.6 24.0 32.0 -40 80

PPU 11.8 19.1 24.7 -55 125

PPT Capacitors -28.1 -13.1 6.6 N/A 125

Thrusters -26.8 -10.7 10.4 -40 100

Predicted Temps (°C) Operational Limits

Overall Model: Cold Case

Component

Min Ave Max Cold Hot

Cameras -25.2 3.3 53.7 -20 60

Rate gyros 10.3 11.4 12.6 -40 80

Magnetometer -8.7 20.0 51.2 -40 85

D/L transmitter 16.4 36.3 61.9 -20 70

U/L receiver 6.4 33.3 52.2 -20 70

Predicted Temps (°C) Operational Limits

Overall Model: Cold Case

Component

Min Ave Max Cold Hot

GPS filter -8.3 3.8 20.7 0 50

GPS isolator -18.1 -16.2 -14.3 0 50

GPS NCLT 21.4 21.6 21.8 0 50

GPS preamp -7.9 4.0 20.1 0 50

GPS switch -18.1 -16.1 -14.1 0 50

Predicted Temps (°C) Operational Limits

Overall Model: Hot Case

Component

Min Ave Max Cold Hot

Batteries 48.7 49.3 50.0 5 20

Boards 26.0 29.2 37.2 -40 80

PPU 56.4 63.3 68.6 -55 125

PPT Capacitors -20.4 -6.0 13.1 N/A 125

Thrusters -20.0 -4.5 16.0 -40 100

Predicted Temps (°C) Operational Limits

Overall Model: Hot Case

Component

Min Ave Max Cold Hot

Cameras -21.2 7.3 57.8 -20 60

Rate gyros 15.6 16.7 17.9 -40 80

Magnetometer -3.1 25.3 56.4 -40 85

D/L transmitter 23.5 42.9 68.3 -20 70

U/L receiver 11.6 37.9 56.5 -20 70

Predicted Temps (°C) Operational Limits

Overall Model: Hot Case

Component

Min Ave Max Cold Hot

GPS filter -4.7 7.2 24.1 0 50

GPS isolator -14.2 -12.4 -10.5 0 50

GPS NCLT 45.4 45.5 45.7 0 50

GPS preamp -4.2 7.5 23.5 0 50

GPS switch -14.3 -12.3 -10.4 0 50

Predicted Temps (°C) Operational Limits

Parametric Study: Battery Box

Batteries

Min Ave Max Cold Hot

Hot Case 17.3 22.8 28.5 5 20

Cold Case 11.8 17.5 23.3 5 20

Predicted Temps (°C) Operational Limits

• Assumed thermal filler (h = 14000 W/m2°C) used at bolted interface between battery box frame and nadir panel

Parametric Study: Effect of h

• Assumed h = 1000 W/m2°C at all bolted interfaces

• Variance of less than ±2 °C in most component temperatures

• In general, the variance indicated that a lower value of h is conservative

Plans

• Verify G’s with CEE, battery box testing

• Study effects of MLI

• Procure interface materials (indium tape)

• Examine possibility of heater control for cold components

• Study survival and shuttle bay environments

Recap

• Thermal models

• Results from models

• Parametric studies

• Future plans

Conclusions

• Detailed thermal model of HokieSat has been generated and tested

• Additional analyses are necessary

• Verification of model with test data desired

• Some changes to the thermal design are required