Thermal Control SubsystemThermal Control Subsystem•Objective:Objective:

To maintain all the components of the satellite within their To maintain all the components of the satellite within their respective temperature limits during all modes of respective temperature limits during all modes of operation.operation.

Formulate ObjectiveFormulate Objective Identify the enemyIdentify the enemy Gear for BattleGear for Battle Plan of AttackPlan of Attack Rally CryRally Cry

Guide to Our JourneyGuide to Our Journey

Sources of Thermal EnergySources of Thermal Energy

Solar RadiationSolar Radiation Albedo Albedo Earth emitted Earth emitted

infraredinfrared heat generated heat generated

by onboard by onboard equipment.equipment.

Methods of ControlMethods of Control

• Passive Control Passive Control relies relies on conductive and radiative on conductive and radiative heat paths and relies on no heat paths and relies on no electrical or mechanical electrical or mechanical input.input.

• Active Control Active Control relies on relies on pumps, thermostats, moving pumps, thermostats, moving parts, and rely on electrical parts, and rely on electrical power.power.

Passive Control ComponentsPassive Control Components

RadiatorRadiator Device with a large surface area used to radiate heat into space.Device with a large surface area used to radiate heat into space. Sizing depends on heat loads and temperature requirements.Sizing depends on heat loads and temperature requirements. This is the primary system of heat rejection on spacecraft. This is the primary system of heat rejection on spacecraft.

Passive Control ComponentsPassive Control Components

Phase Change DevicesPhase Change Devices Absorbs thermal energy by Absorbs thermal energy by

changing from a solid to a liquid.changing from a solid to a liquid. Useful for electrical equipment that Useful for electrical equipment that

experiences short power spikes.experiences short power spikes. Disadvantaged by inability to Disadvantaged by inability to

absorb heat upon melting.absorb heat upon melting. A common type consists of some A common type consists of some

sort of wax in an aluminum sort of wax in an aluminum container, resting between the heat container, resting between the heat dissipating device and a cold plate. dissipating device and a cold plate.

Thermal Control CoatingThermal Control Coating Coatings such as white/black, or Coatings such as white/black, or

gold or silver foil, have special gold or silver foil, have special radiation properties which govern radiation properties which govern heat transfer through applied surface.heat transfer through applied surface.

It is desirable to have a highly It is desirable to have a highly emissive and minimally absorbing emissive and minimally absorbing surface to reject as much heat into surface to reject as much heat into space as possible without collecting space as possible without collecting much.much.

Very efficient and light weight, but Very efficient and light weight, but its performance will degrade over its its performance will degrade over its lifetime. lifetime.

Multi-Layer InsulationMulti-Layer Insulation Closely spaced layer of aluminized Closely spaced layer of aluminized

Kapton or Mylar alternated with a Kapton or Mylar alternated with a course netted material.course netted material.

Reduces the amount of heat flow Reduces the amount of heat flow per unit area between two per unit area between two boundary surfaces and prevents a boundary surfaces and prevents a large heat influx.large heat influx.

Sensors and payloads can be Sensors and payloads can be wrapped with MLI, to thermally wrapped with MLI, to thermally isolate them and reduce thermal isolate them and reduce thermal control requirements.control requirements.

Thermal DoublersThermal Doublers Effectively a heat sink, a highly Effectively a heat sink, a highly

conductive material is placed in conductive material is placed in thermal contact with a material.thermal contact with a material.

Prevents severe cooling/heating.Prevents severe cooling/heating. Commonly used to control Commonly used to control

temperature of electrical equipment temperature of electrical equipment that is subject to cyclical power that is subject to cyclical power dissipation.dissipation.

Also can be used to spread heat out Also can be used to spread heat out over radiator surfaces.over radiator surfaces.

Passive Control ComponentsPassive Control Components

Passive/Active Control Passive/Active Control ComponentsComponents

Cold PlatesCold Plates Used for mounting heat dissipating equipment.Used for mounting heat dissipating equipment. In an active system there are fluid passages within the plate itself. This In an active system there are fluid passages within the plate itself. This

fluid is pumped to a radiator where it dumps its absorbed heat and begins fluid is pumped to a radiator where it dumps its absorbed heat and begins the cycle againthe cycle again

In a passive system, the cold plate is usually combined with the radiator. In a passive system, the cold plate is usually combined with the radiator.

Active Control ComponentsActive Control Components

Heat PipeHeat Pipe Heat dissipated by evaporation and condensation.Heat dissipated by evaporation and condensation. Thermal energy absorbed by liquid contained within the pipe. Liquid is turned into gas Thermal energy absorbed by liquid contained within the pipe. Liquid is turned into gas

where it travels to the other end of the pipe, where it releases the energy to a radiator where it travels to the other end of the pipe, where it releases the energy to a radiator upon condensing back to a liquid.upon condensing back to a liquid.

Pipe is usually made of aluminum and the liquid is usually ammonia.Pipe is usually made of aluminum and the liquid is usually ammonia. Heat pipes provide a highly conductive heat path and extremely high heat transfer rates.Heat pipes provide a highly conductive heat path and extremely high heat transfer rates.

Active Control ComponentsActive Control Components

LouversLouvers Mounted on the surface of the radiator, they act like Mounted on the surface of the radiator, they act like

Venetian blinds that can be opened and closed.Venetian blinds that can be opened and closed. Different thermal coatings are applied to the blades Different thermal coatings are applied to the blades

and the base plate .and the base plate . The absorptive and emmissive thermo-optical The absorptive and emmissive thermo-optical

properties of the radiator can be varied by opening and properties of the radiator can be varied by opening and closing the blades by use of actuators.closing the blades by use of actuators.

Offer a controlled rate of heat transfer, but can result in Offer a controlled rate of heat transfer, but can result in high temperatures if pointed toward sun. high temperatures if pointed toward sun.

Second Surface Mirrors are more cutting edge and Second Surface Mirrors are more cutting edge and have all but replaced louvers in industry. Instead of have all but replaced louvers in industry. Instead of louvers with different coatings, mirrors act to reflect louvers with different coatings, mirrors act to reflect incident radiation while radiating out internal energyincident radiation while radiating out internal energy

Active Control ComponentsActive Control Components

Thermal SwitchThermal Switch Provides a direct conduction path Provides a direct conduction path

between a heat source and the between a heat source and the equipment mounting plate when equipment mounting plate when the switch is closed.the switch is closed.

Electrical HeaterElectrical Heater Controlled by a thermostat, and Controlled by a thermostat, and

used to heat cold regions of the used to heat cold regions of the satellite.satellite.

Heat is generated by running Heat is generated by running current through a resistor.current through a resistor.

Generally used for fine temperature Generally used for fine temperature control and for short periods of control and for short periods of time.time.

Begin with Passive System, adding Begin with Passive System, adding components as neededcomponents as needed

Use active system if there is only a Use active system if there is only a few degrees of tolerance in the few degrees of tolerance in the required temperature or if several required temperature or if several kilowatts are to be dissipatedkilowatts are to be dissipated

Design is typically modeled for the Design is typically modeled for the coldest casecoldest case

Typical industrial results are for the Typical industrial results are for the thermal subsystem to make up 3-thermal subsystem to make up 3-4% of the overall weight and cost 4% of the overall weight and cost of the satellite.of the satellite.

Design ProcessDesign Process

ConclusionConclusion Teamwork is essential to survival Ideas must be communicated

• http://www.esa.int/est/prod/prod0661.htmhttp://www.esa.int/est/prod/prod0661.htm

• http://www.srh.noaa.gov/lch/prep/heat.jpghttp://www.srh.noaa.gov/lch/prep/heat.jpg

• http://engineering.dartmouth.edu/~dartsat/albedo.jpghttp://engineering.dartmouth.edu/~dartsat/albedo.jpg

• http://www.tsgc.utexas.edu/archive/subsystems/thermal.pdfhttp://www.tsgc.utexas.edu/archive/subsystems/thermal.pdf

• Barter, Neville J. “Space Data” Northrup Grumman Space Barter, Neville J. “Space Data” Northrup Grumman Space Technology, 5Technology, 5thth ed. (2002) ed. (2002)

• Wertz, James R. and Larson, Wiley J. “Space Mission Analysis and Wertz, James R. and Larson, Wiley J. “Space Mission Analysis and Design”, Microcosm Press, 3Design”, Microcosm Press, 3rdrd ed. (1999) ed. (1999)

ReferencesReferences