Spacecraft Thermal Control Handbook
Spacecraft must protect their components from environmental elements and prevent excessive heating from them, this includes minimizing heat lost to space and eliminating dissipated environmental fluxes.
SmallSats often employ passive thermal control elements such as multilayer insulation (MLI) blankets to maintain component temperature limits. MLI blankets serve two important purposes – they both prevent heat losses into space as well as overabsorbence of solar radiation by components.
Introduction
Spacecraft thermal control is an integral component of any space mission, ensuring that components stay within their temperature limits at all times. This handbook introduces fundamentals of spacecraft thermal control as well as current technologies.
It covers essential aspects of spacecraft design, analysis, integration, and testing as well as cryogenic cooling systems. It aims to motivate early career engineers as well as students enrolled in space-related courses to begin conducting thermal analyses and contributing their designs into spacecraft systems.
Chapter 1: The Space Environment
Space environments are integral parts of every spacecraft design, ensuring its components operate at acceptable temperature ranges. They include sunlight, albedo and planetary radiation as well as internal heat sources like integrated circuits.
Spacecraft must also accommodate aerodynamic heating during launch and reentry, as well as effects such as plasma interactions, micrometeoroid/orbital debris environments, electrostatic charging and upper atmospheric drag; all these elements have an effect on thermal control design and spacecraft materials.
Chapter 2: Heat Transfer Processes
Spacecraft thermal control can be achieved through balancing the energy it receives from space and dissipates internally through equipment, while simultaneously compensating for energy dissipation from it. This energy comes from sources like solar radiation intensity JS, albedo radiation intensity JA and infrared radiation intensity JP.
To ensure temperature management systems (TMSs) are suitable for an orbital environment, their thermophysical properties must be tested in a simulated ground environment. This information will aid the design of passive and active technologies and materials.
Chapter 3: Thermal Design
Most sophisticated space equipment requires a certain temperature range in order to function optimally, and TCS’s role is to keep everything onboard the spacecraft within those pre-defined limits throughout its mission phases.
Passive thermal control methods like multi-layer insulation (MLI), thermal coatings and heat pipes are employed to restore equilibrium within an environment.
Efficiency depends on physical characteristics of the blanket (number and types of layers) as well as how well distributed it is on the spacecraft surface.
Chapter 4: Thermal Control Hardware
Spacecraft thermal control focuses on maintaining the physical integrity and optimal performance of electronic equipment in space, to safeguard its physical integrity as well as performance. Temperature regulation must be achieved to avoid damage due to extreme temperatures while making sure critical components such as optical sensors or atomic clocks operate within their optimal temperature ranges.
Due to their size and limited electrical energy, traditional thermal control elements like louvers and heaters do not scale well with satellite designs, making passive thermal control technologies increasingly essential in this domain.
Chapter 5: Thermal Analysis
All spacecraft equipment must operate within its temperature range for proper functioning. This range is determined by how much solar radiation is absorbed, as well as the heat transferred and dissipated through its journey through space.
This chapter presents basic formulas and modeling methods for thermal analysis of LEO satellites. These techniques are simple enough that spreadsheets or software tools may be utilized. Engineers can utilize thermal analysis of electronic subsystems without resorting to costly EEE component-level FEA modeling techniques.
Chapter 6: Thermal Testing
Spacecraft manufacturers and customers rely on ground-based thermal testing to ensure their products will perform as promised in space’s harsh environments. Such tests often use thermal shock chambers or vacuum chambers to simulate the harsh thermal environments and extreme temperatures that could occur while orbital flight.
Coatings are paint or more advanced chemicals applied to a spacecraft’s exterior in order to minimize its absorption of environmental fluxes and maximize heat emission to spacecraft environment. Most commonly these coatings use materials with low solar absorptivity and high infrared (IR) emittivity as components of their composition.
Spacecraft are subjected to an array of thermal environments, which necessitate unique design considerations for them. These may include long interplanetary journeys near or far from the Sun, descent through hostile atmospheres or extended eclipse durations.
Satellite thermal control systems use various techniques to maintain acceptable operational temperatures throughout each mission phase for spacecraft components. Surface finishes, insulation materials, radiators and louvers are often employed as methods of temperature regulation.
Coatings
Coatings can help satellites maintain consistent internal temperatures by reflecting and absorbing solar radiation, helping prevent overheating of key components and maintaining consistent internal temperatures over time.
Thermal control coatings can be applied to various surfaces, including satellite structures and electronics. The ideal choice depends on factors like geometry, material requirements and thermal requirements – aerogels provide lightweight insulation while keeping sensitive electronic components cool.
Metallic coatings, on the other hand, are designed to reflect sunlight and dissipate heat efficiently while withstanding rapid temperature changes found in space. Manufacturers conduct tests on thermal shock resistance, thermal conductivity and emissivity (the latter of which involves subjecting coated samples to solar irradiance in an evacuated chamber at cold temperatures) in order to assess performance of such coatings.
Sunshields
Space thermal environments vary across planetary orbit or interplanetary missions, with most spacecraft components having temperature ranges they must stay within throughout their flight phases. The amount of solar and infrared (IR) radiation a spacecraft absorbs and radiates back out is dictated by Eq. 1.
Solar absorptivity and total hemispherical IR emissivity aS/eH are among the key properties that play into heat exchange between spacecraft and their respective planets. These two properties determine what proportion of an object’s infrared radiation is emitted into space compared to what would happen with an ideal blackbody emitter at that temperature.
To maintain spacecraft component temperatures, active devices are needed to expel heat away from its components into space. These must be lightweight and consume no power when operating; louvers are commonly used as these active devices – though other devices such as variable emissivity materials and thermochromic materials could also work.
Louvers
Given the increasing sophistication of instruments on small spacecraft with long missions, thermal control is becoming an indispensable technology. Since smaller volumes absorb and release heat more rapidly than larger bodies do, game-changing solutions must be found to maintain stable thermal environments aboard spacecraft.
Louvers are an efficient passive thermal control component designed to maintain internal spacecraft temperature stability by creating a difference of several watts between closed and open louvers, dissipation difference created between closed and open louvers, and creating power dissipation differences of several watts between their closed and open states. Their design is inspired by full-sized radiators modified for CubeSat form factor; bimetallic clock springs whose thermal expansion rates differ between their fused metals create bimetallic clock springs which open upon heating; once the springs expand upon rising temperatures when temperatures increase springs expand opening the louvers while changing average surface IR emittivity of radiator surface by altering its average surface average surface average IR emission level by several percent or so.
Other passive thermal control technologies include thermal straps made of Mylar foil or Boyd’s k-core pyrolytic graphite sheets. Utah State University has utilized these straps to increase thermal rejection and zonal temperature regulation on satellite busses and payloads.
MLI
Spacecraft components must maintain specific temperatures in order to meet survival and functional requirements across all mission stages, which requires balancing heat absorbed, stored, produced, dissipated or exchanged via solar absorptivity, infrared (IR) emission from surface optical properties or thermal capacitance.
Passive thermal control enables spacecraft with limited cost, volume, weight, and power requirements such as SmallSats and CubeSats to maintain component temperatures without using powered equipment, making this approach particularly appealing. Passive technologies include MLI (Mass Loaded Instrumentation), coatings/surface finishes thermal straps interface conductance as well as sunshades.
MLI blankets are typically constructed of multiple layers of thin material with low infrared (IR) emissivity that have been embossed or alternated with thinner netting to limit conduction, as well as perforations to vent trapped air once in orbit. MLI offers high TRL ratings and fits many different SmallSat form factors, though its performance drops considerably when compressed into compact sizes, potentially creating hazards when deployed via pusher spring deployers found on some SmallSats.
Spacecraft are subjected to an array of thermal environments, which necessitate unique design considerations for them. These may include long interplanetary journeys near or far from the Sun, descent through hostile atmospheres or extended eclipse durations.
Satellite thermal control systems use various techniques to maintain acceptable operational temperatures throughout each mission phase for spacecraft components. Surface finishes, insulation materials, radiators and louvers are often employed as methods of temperature regulation.
Coatings
Coatings can help satellites maintain consistent internal temperatures by reflecting and absorbing solar radiation, helping prevent overheating of key components and maintaining consistent internal temperatures over time.
Thermal control coatings can be applied to various surfaces, including satellite structures and electronics. The ideal choice depends on factors like geometry, material requirements and thermal requirements – aerogels provide lightweight insulation while keeping sensitive electronic components cool.
Metallic coatings, on the other hand, are designed to reflect sunlight and dissipate heat efficiently while withstanding rapid temperature changes found in space. Manufacturers conduct tests on thermal shock resistance, thermal conductivity and emissivity (the latter of which involves subjecting coated samples to solar irradiance in an evacuated chamber at cold temperatures) in order to assess performance of such coatings.
Sunshields
Space thermal environments vary across planetary orbit or interplanetary missions, with most spacecraft components having temperature ranges they must stay within throughout their flight phases. The amount of solar and infrared (IR) radiation a spacecraft absorbs and radiates back out is dictated by Eq. 1.
Solar absorptivity and total hemispherical IR emissivity aS/eH are among the key properties that play into heat exchange between spacecraft and their respective planets. These two properties determine what proportion of an object’s infrared radiation is emitted into space compared to what would happen with an ideal blackbody emitter at that temperature.
To maintain spacecraft component temperatures, active devices are needed to expel heat away from its components into space. These must be lightweight and consume no power when operating; louvers are commonly used as these active devices – though other devices such as variable emissivity materials and thermochromic materials could also work.
Louvers
Given the increasing sophistication of instruments on small spacecraft with long missions, thermal control is becoming an indispensable technology. Since smaller volumes absorb and release heat more rapidly than larger bodies do, game-changing solutions must be found to maintain stable thermal environments aboard spacecraft.
Louvers are an efficient passive thermal control component designed to maintain internal spacecraft temperature stability by creating a difference of several watts between closed and open louvers, dissipation difference created between closed and open louvers, and creating power dissipation differences of several watts between their closed and open states. Their design is inspired by full-sized radiators modified for CubeSat form factor; bimetallic clock springs whose thermal expansion rates differ between their fused metals create bimetallic clock springs which open upon heating; once the springs expand upon rising temperatures when temperatures increase springs expand opening the louvers while changing average surface IR emittivity of radiator surface by altering its average surface average surface average IR emission level by several percent or so.
Other passive thermal control technologies include thermal straps made of Mylar foil or Boyd’s k-core pyrolytic graphite sheets. Utah State University has utilized these straps to increase thermal rejection and zonal temperature regulation on satellite busses and payloads.
MLI
Spacecraft components must maintain specific temperatures in order to meet survival and functional requirements across all mission stages, which requires balancing heat absorbed, stored, produced, dissipated or exchanged via solar absorptivity, infrared (IR) emission from surface optical properties or thermal capacitance.
Passive thermal control enables spacecraft with limited cost, volume, weight, and power requirements such as SmallSats and CubeSats to maintain component temperatures without using powered equipment, making this approach particularly appealing. Passive technologies include MLI (Mass Loaded Instrumentation), coatings/surface finishes thermal straps interface conductance as well as sunshades.
MLI blankets are typically constructed of multiple layers of thin material with low infrared (IR) emissivity that have been embossed or alternated with thinner netting to limit conduction, as well as perforations to vent trapped air once in orbit. MLI offers high TRL ratings and fits many different SmallSat form factors, though its performance drops considerably when compressed into compact sizes, potentially creating hazards when deployed via pusher spring deployers found on some SmallSats.