Tavo Ani MATERIALS AND METHODS USED IN THERMAL CONTROL SYSTEM

TEMPERATURE RANGES Divided to 3 main range: <200K cryogenic range 200 to 470 K conventional range >470 K high-temperature range

CRYOGENIC RANGE Temperatures below 200 K Used for special equipment, like optical systems

CONVENTIONAL RANGE Temperature range from 200 K to 470 K Most space applications run in this range Usually for inside components -40 to 50 C For outside components -170 to 90 C

HIGH-TEMPERATURE RANGE Range >470 K Mainly heat protection bodies For re-entry bodies

ENVIRONMENT IN SPACE Things to consider while in space: Near absolute vacuum, thus, no need to mess with Convection Background temperature about 2.7 K in shadow Large radiant fluxes

ENERGY BALANCE Thermal dissipation of the satellite Absorotion of solar energy, Earth infrared Heat leak through insulation Radiated heat Heat loss through insulation

ORBITAL CONDITIONS Need to count with shadow area of planet In case of atmosphere, friction and degradation at lower altitudes Infrared radiation from a planet Albedo effect

SOLAR CONSTANT Shows radiance of sun on Earth orbit S=S0[ *cos(360¤*n/365)] where n=day of the year S0=1371 W/m^2 Maximum radiation at perihelion (January 3rd) is 1428 W/m^2 Minimum radiation at aphelion (July 4th) is 1316 W/m^2

ALBEDO Defined as the reflection of a body Considered about for Earth Can vary from 5 to 60 % ~480 W/m^2

Solar Probe Plus Descendant of Solar Probe Launched in May 2015 Periphelion 6,000,000 km from sun Total on 24 solar passes, 961 hours of it nearer then 1,360,000 km Solar flux at it’s closest point 4,000,000 W/m^2 (1371 W/m^2 at Earth’s orbit) Sun shield will be at that moment about 1700 K TO GO WHERE NO PROBE HAS GONE BEFORE

HEAT TRANSFER (HT)

MATERIALS PROPERTIES FOR THERMAL ENGINEER

Passive methods: Simple No interface needed Doesn’t need any power Used preferably Active methods: Used only if passive methods are not sufficient Needs power Gives more error range for thermal calculations METHODS OF THERMAL CONTROL

PASSIVE METHODS Coatings Insulation: Multilayer insulation (MLI) Aerogel (sub-atmospheric missions) Radiators Phase change materials Heat switches

COATINGS

Cheapest method of getting satisfying radiative results Easiest to mount Suffers on degradation, not the best method for long-term missions α-solar absorbance ε-radiative emittance Basic rule of α/ε High α/ε factor: Radiators Low α/ε factor: Heaters PAINTS Surface coating Solar absorpti on(α) Emissivit y(ε) α/εα/ε White paint Black paint Vapor- deposited Aluminu m Gold Silver

OSR/SSM

Atomic Oxygen(AO) Major damager of the LEO environment Causes erosion of SC materials at altitudes 100 to 1000 km DEGRADATION

MLI

AEROGELS

RADIATORS

PHASE CHANGE MATERIALS (PCM) Used for high-power-dissipating components, which are turned on occasionally Concept is to prevent cooling below operating temperatures

Most heat switches are passive Switch roles between good thermal conductors and thermal insulators Allows to control the temperature of heat producing component HEAT SWITCHES

ACTIVE METHODS Heaters Louvers Pumped fluid loops Heat pipes Thermoelectric coolers

Things to use in case of non ideal circumstances Objectives: To protect components from cold- case scenarios Balancing heat not generated by turned off electronics Warming up electronics to their minimum operating temperature HEATERS

LOUVERS Allows better heat rejection if needed Able to also modulate heat transfer between internal SC components Work in shadow and sunlight Consists of 5 elements: Baseplate Blades Actuators Sensing elements Structural elements

PUMPED FLUID LOOPS Provides trasnfer of a large amount of thermal energy between two points Heat is either emitted by radiation or with coolant directly to space

Two phase liquid flow cycle Doesn’t need electrical power Able to transport relatively large quantities of heat Fixed working range Russian’s Loop heat pipes(LHP) American Capillary pumped loops(CPL) HEAT PIPES

THERMOELECTRIC COOLERS Miniature solid-state heat pump Provides localized cooling Cooling is provided via Peltiter effect

ÜLESANNE Soojusvahetus L-kujulise detaili seinte vahel, mille küljed on 100mm ja 161mm ning laius 260mm Keha kiiritatakse väiksema tahu pealt 1460 W/m^2 Materjaliks on Alumiinium 6061-T6 Leia, missugune soojusülekanne toimub L-detaili alumiselt seinalt ülemisele seinale, kui detaili paksus on 1 mm. PS! Lihtsustuseks 1mm paksustelt ribadelt eraldunud kiirgust mitte arvestada. Mis tulemus saada, kui pind üle kullata? Bulk Al6061T6 Density 2700 Specific Heat 896 Conductivity 167

REFERENCES 1.David G. Gilmore “Spacecraft Thermal Control Handbook Volume 1: Fundamental Technologies” Wilfried Ley „Handbook of Space Technology“ Peter L. Conley „Space Vehicle Mechanisms“ 4.