Transcript Peer Review 5/30/03 - Colorado Space Grant Consortium

Thermal Control Subsystem
•Objective:
To maintain all the components of the satellite within their
respective temperature limits during all modes of operation.
Guide to Our Journey
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Formulate Objective
Identify the enemy
Gear for Battle
Plan of Attack
Rally Cry
Sources of Thermal Energy
 Solar Radiation
 Albedo
 Earth emitted
infrared
 heat generated
by onboard
equipment.
Methods of Control
• Passive Control relies
on conductive and radiative
heat paths and relies on no
electrical or mechanical input.
• Active Control relies on
pumps, thermostats, moving
parts, and rely on electrical
power.
Passive Control Components
Radiator
 Device with a large surface area used to radiate heat into space.
 Sizing depends on heat loads and temperature requirements.
 This is the primary system of heat rejection on spacecraft.
Passive Control Components
Phase Change Devices
 Absorbs thermal energy by
changing from a solid to a liquid.
 Useful for electrical equipment that
experiences short power spikes.
 Disadvantaged by inability to
absorb heat upon melting.
 A common type consists of some
sort of wax in an aluminum
container, resting between the heat
dissipating device and a cold plate.
Thermal Control Coating
 Coatings such as white/black, or gold
or silver foil, have special radiation
properties which govern heat transfer
through applied surface.
 It is desirable to have a highly
emissive and minimally absorbing
surface to reject as much heat into
space as possible without collecting
much.
 Very efficient and light weight, but
its performance will degrade over its
lifetime.
Passive Control Components
Multi-Layer Insulation
 Closely spaced layer of aluminized
Kapton or Mylar alternated with a
course netted material.
 Reduces the amount of heat flow
per unit area between two boundary
surfaces and prevents a large heat
influx.
 Sensors and payloads can be
wrapped with MLI, to thermally
isolate them and reduce thermal
control requirements.
Thermal Doublers
 Effectively a heat sink, a highly
conductive material is placed in
thermal contact with a material.
 Prevents severe cooling/heating.
 Commonly used to control
temperature of electrical equipment
that is subject to cyclical power
dissipation.
 Also can be used to spread heat out
over radiator surfaces.
Passive/Active Control
Components
Cold Plates
 Used for mounting heat dissipating equipment.
 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 the cycle again
 In a passive system, the cold plate is usually combined with the radiator.
Active Control Components
Heat Pipe
 Heat dissipated by evaporation and condensation.
 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
upon condensing back to a liquid.
 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.
Active Control Components
Louvers
 Mounted on the surface of the radiator, they act like
Venetian blinds that can be opened and closed.
 Different thermal coatings are applied to the blades
and the base plate .
 The absorptive and emmissive thermo-optical
properties of the radiator can be varied by opening and
closing the blades by use of actuators.
 Offer a controlled rate of heat transfer, but can result in
high temperatures if pointed toward sun.
 Second Surface Mirrors are more cutting edge and
have all but replaced louvers in industry. Instead of
louvers with different coatings, mirrors act to reflect
incident radiation while radiating out internal energy
Active Control Components
Thermal Switch
 Provides a direct conduction path
between a heat source and the
equipment mounting plate when
the switch is closed.
Electrical Heater
 Controlled by a thermostat, and
used to heat cold regions of the
satellite.
 Heat is generated by running
current through a resistor.
 Generally used for fine temperature
control and for short periods of
time.
Design Process
 Begin with Passive System, adding
components as needed
 Use active system if there is only a
few degrees of tolerance in the
required temperature or if several
kilowatts are to be dissipated
 Design is typically modeled for the
coldest case
 Typical industrial results are for the
thermal subsystem to make up 34% of the overall weight and cost
of the satellite.
Conclusion
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Teamwork is essential to survival
Ideas must be communicated
References
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http://www.esa.int/est/prod/prod0661.htm
http://www.srh.noaa.gov/lch/prep/heat.jpg
http://engineering.dartmouth.edu/~dartsat/albedo.jpg
http://www.tsgc.utexas.edu/archive/subsystems/thermal.pdf
Barter, Neville J. “Space Data” Northrup Grumman Space
Technology, 5th ed. (2002)
• Wertz, James R. and Larson, Wiley J. “Space Mission Analysis and
Design”, Microcosm Press, 3rd ed. (1999)