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In spacecraft design, the function of the thermal control system (TCS) is to keep all the spacecraft's component systems within acceptable temperature ranges during all mission phases. It must cope with the external environment, which can vary in a wide range as the spacecraft is exposed to the extreme coldness found in the shadows of deep space or to the intense heat found in the unfiltered direct sunlight of outer space. A TCS must also moderate the internal heat generated by the operation of the spacecraft it serves.
A TCS can eject heat passively through the simple and natural infrared radiation of the spacecraft itself, or actively through an externally mounted infrared radiation coil.
Thermal control is essential to guarantee the optimal performance and success of the mission because if a component is subjected to temperatures which are too high or too low, it could be damaged or its performance could be severely affected. Thermal control is also necessary to keep specific components (such as optical sensors, atomic clocks, etc.) within a specified temperature stability requirement, to ensure that they perform as efficiently as possible.
The thermal control subsystem can be composed of both passive and active items and works in two ways:
Passive thermal control system (PTCS) components include:
Active thermal control system (ATCS) components include:
For a spacecraft the main environmental interactions are the energy coming from the Sun and the heat radiated to deep space. Other parameters also influence the thermal control system design such as the spacecraft's altitude, orbit, attitude stabilization, and spacecraft shape. Different types of orbit, such as low Earth orbit and geostationary orbit, also affect the design of the thermal control system.
The temperature requirements of the instruments and equipment on board are the main factors in the design of the thermal control system. The goal of the TCS is to keep all the instruments working within their allowable temperature range. All of the electronic instruments on board the spacecraft, such as cameras, data-collection devices, batteries, etc., have a fixed operating temperature range. Keeping these instruments in their optimal operational temperature range is crucial for every mission. Some examples of temperature ranges include
Coatings are the simplest and least expensive of the TCS techniques. A coating may be paint or a more sophisticated chemical applied to the surfaces of the spacecraft to lower or increase heat transfer. The characteristics of the type of coating depends on their absorptivity, emissivity, transparency, and reflectivity. The main disadvantage of coating is that it degrades quickly due to the operating environment. Coatings can also be applied in the form of adhesive tape or stickers to reduce degradation.
Multilayer insulation (MLI) is the most common passive thermal control element used on spacecraft. MLI prevents both heat losses to the environment and excessive heating from the environment. Spacecraft components such as propellant tanks, propellant lines, batteries, and solid rocket motors are also covered in MLI blankets to maintain ideal operating temperature. MLI consist of an outer cover layer, interior layer, and an inner cover layer. The outer cover layer needs to be opaque to sunlight, generate a low amount of particulate contaminates, and be able to survive in the environment and temperature to which the spacecraft will be exposed. Some common materials used for the outer layer are fiberglass woven cloth impregnated with PTFE Teflon, PVF reinforced with Nomex bonded with polyester adhesive, and FEP Teflon. The general requirement for the interior layer is that it needs to have a low emittance. The most commonly used material for this layer is Mylar aluminized on one or both sides. The interior layers are usually thin compared to the outer layer to save weight and are perforated to aid in venting trapped air during launch. The inner cover faces the spacecraft hardware and is used to protect the thin interior layers. Inner covers are often not aluminized in order to prevent electrical shorts. Some materials used for the inner covers are Dacron and Nomex netting. Mylar is not used because of flammability concerns. MLI blankets are an important element of the thermal control system.
Louvers are active thermal control elements that are used in many different forms. Most commonly they are placed over external radiators, louvers can also be used to control heat transfer between internal spacecraft surfaces or be placed on openings on the spacecraft walls. A louver in its fully open state can reject six times as much heat as it does in its fully closed state, with no power required to operate it. The most commonly used louver is the bimetallic, spring-actuated, rectangular blade louver also known as venetian-blind louver. Louver radiator assemblies consist of five main elements: baseplate, blades, actuators, sensing elements, and structural elements.
Heaters are used in thermal control design to protect components under cold-case environmental conditions or to make up for heat that is not dissipated. Heaters are used with thermostats or solid-state controllers to provide exact temperature control of a particular component. Another common use for heaters is to warm up components to their minimal operating temperatures before the components are turned on.
Excess waste heat created on the spacecraft is rejected to space by the use of radiators. Radiators come in several different forms, such as spacecraft structural panels, flat-plate radiators mounted to the side of the spacecraft, and panels deployed after the spacecraft is on orbit. Whatever the configuration, all radiators reject heat by infrared (IR) radiation from their surfaces. The radiating power depends on the surface's emittance and temperature. The radiator must reject both the spacecraft waste heat and any radiant-heat loads from the environment. Most radiators are therefore given surface finishes with high IR emittance to maximize heat rejection and low solar absorptance to limit heat from the Sun. Most spacecraft radiators reject between 100 and 350 W of internally generated electronics waste heat per square meter. Radiators' weight typically varies from almost nothing, if an existing structural panel is used as a radiator, to around 12 kg/m2 for a heavy deployable radiator and its support structure.
The radiators of the International Space Station are clearly visible as arrays of white square panels attached to the main truss. [1]
Heat pipes use a closed two-phase liquid-flow cycle with an evaporator and a condenser to transport relatively large quantities of heat from one location to another without electrical power. Aerospace-grade specific heat pipes such as Constant Conductance Heat Pipes (CCHPs) or Axial Groove heat pipes are aluminum extrusions with ammonia used as the working fluid. Typical Applications Include: Payload thermal management Heat transport, Isothermalization, Radiator panel thermal enhancement [2]
A major event in the field of space thermal control is the International Conference on Environmental Systems, organized every year by AIAA. Another is the European Space Thermal Analysis Workshop
In spacecraft design, a Sun shield restricts or reduces heat caused by sunlight hitting a spacecraft. [5] An example of use of a thermal shield is on the Infrared Space Observatory. [5] The ISO sunshield helped protect the cryostat from sunlight, and it was also covered with solar panels. [6]
Not to be confused with the concept of a global-scale Sun shield in geoengineering, often called a Space sunshade or "Sun shield", in which the spacecraft itself is used to block sunlight to a planet. [7]
An example of a sunshield in spacecraft design is the sunshield on the James Webb Space Telescope. [8]
A radiator is a heat exchanger used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics.
In the study of heat transfer, radiative cooling is the process by which a body loses heat by thermal radiation. As Planck's law describes, every physical body spontaneously and continuously emits electromagnetic radiation.
Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. Thermal radiation transmits as an electromagnetic wave through both matter and vacuum. When matter absorbs thermal radiation its temperature will tend to rise. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electronic, molecular, and lattice oscillations in a material. Kinetic energy is converted to electromagnetism due to charge-acceleration or dipole oscillation. At room temperature, most of the emission is in the infrared (IR) spectrum. Thermal radiation is one of the fundamental mechanisms of heat transfer, along with conduction and convection.
In engineering, a heat shield is a component designed to protect an object or a human operator from being burnt or overheated by dissipating, reflecting, and/or absorbing heat. The term is most often used in reference to exhaust heat management and to systems for dissipating frictional heat. Heat shields are used most commonly in automotive and aerospace.
A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces.
A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and solar towers or non water heating devices such as solar cooker, solar air heaters.
Kapton is a polyimide film used in flexible printed circuits and space blankets, which are used on spacecraft, satellites, and various space instruments. Invented by the DuPont Corporation in the 1960s, Kapton remains stable across a wide range of temperatures, from 4 to 673 K. Kapton is used in electronics manufacturing, space applications, with x-ray equipment, and in 3D printing applications. Its favorable thermal properties and outgassing characteristics result in its regular use in cryogenic applications and in situations where high vacuum environments are experienced.
A radioisotope heater unit (RHU) is a small device that provides heat through radioactive decay. They are similar to tiny radioisotope thermoelectric generators (RTG) and normally provide about one watt of heat each, derived from the decay of a few grams of plutonium-238—although other radioactive isotopes could be used. The heat produced by these RHUs is given off continuously for several decades and, theoretically, for up to a century or more.
Spacecraft design is a process where systems engineering principles are systemically applied in order to construct complex vehicles for missions involving travel, operation or exploration in outer space. This design process produces the detailed design specifications, schematics, and plans for the spacecraft system, including comprehensive documentation outlining the spacecraft's architecture, subsystems, components, interfaces, and operational requirements, and potentially some prototype models or simulations, all of which taken together serve as the blueprint for manufacturing, assembly, integration, and testing of the spacecraft to ensure that it meets mission objectives and performance criteria.
Low emissivity refers to a surface condition that emits low levels of radiant thermal (heat) energy. All materials absorb, reflect, and emit radiant energy according to Planck's law but here, the primary concern is a special wavelength interval of radiant energy, namely thermal radiation of materials. In common use, especially building applications, the temperature range of approximately -40 to +80 degrees Celsius is the focus, but in aerospace and industrial process engineering, much broader ranges are of practical concern.
Underfloor heating and cooling is a form of central heating and cooling that achieves indoor climate control for thermal comfort using hydronic or electrical heating elements embedded in a floor. Heating is achieved by conduction, radiation and convection. Use of underfloor heating dates back to the Neoglacial and Neolithic periods.
Multi-layer insulation (MLI) is thermal insulation composed of multiple layers of thin sheets and is often used on spacecraft and cryogenics. Also referred to as superinsulation, MLI is one of the main items of the spacecraft thermal design, primarily intended to reduce heat loss by thermal radiation. In its basic form, it does not appreciably insulate against other thermal losses such as heat conduction or convection. It is therefore commonly used on satellites and other applications in vacuum where conduction and convection are much less significant and radiation dominates. MLI gives many satellites and other space probes the appearance of being covered with gold foil which is the effect of the amber-coloured Kapton layer deposited over the silver Aluminized mylar.
An optical solar reflector (OSR) is a component of a vehicle or machine designed to fly in outer space. The reflector consists of a top layer made out of quartz, over a reflecting layer made of metal. OSRs are used for radiators on spacecraft.
Jugnu, is an Indian technology demonstration and remote sensing CubeSat satellite which was operated by the Indian Institute of Technology Kanpur. Built under the guidance of Dr. N. S. Vyas, it is a nanosatellite which will be used to provide data for agriculture and disaster monitoring. It is a 3-kilogram (6.6 lb) spacecraft, which measures 34 centimetres (13 in) in length by 10 centimetres (3.9 in) in height and width. Its development programme cost around 25 million rupee. It has a design life of one year.
The International Space Station (ISS) External Active Thermal Control System (EATCS) maintains an equilibrium when the ISS environment or heat loads exceed the capabilities of the Passive Thermal Control System (PTCS). Note Elements of the PTCS are external surface materials, insulation such as Multi-Layer Insulation (MLI), or Heat Pipes. The EATCS provides heat rejection capabilities for all the U.S. pressurized modules, the Japanese Experiment Module (JEM), the Columbus Orbital Facility (COF), and the main power distribution electronics of the S0, S1 and P1 Trusses. The EATCS consists of two independent Loops, which both use mechanically pumped fluid state ammonia in closed-loop circuits. The EATCS is capable of rejecting up to 70 kW, and provides a substantial upgrade in heat rejection capacity from the 14 kW capability of the Early External Active Thermal Control System (EEATCS) via the Early Ammonia Servicer (EAS), which was launched on STS-105 and installed onto the P6 Truss.
Heat exchangers are devices that transfer heat to achieve desired heating or cooling. An important design aspect of heat exchanger technology is the selection of appropriate materials to conduct and transfer heat fast and efficiently.
Radiant heating and cooling is a category of HVAC technologies that exchange heat by both convection and radiation with the environments they are designed to heat or cool. There are many subcategories of radiant heating and cooling, including: "radiant ceiling panels", "embedded surface systems", "thermally active building systems", and infrared heaters. According to some definitions, a technology is only included in this category if radiation comprises more than 50% of its heat exchange with the environment; therefore technologies such as radiators and chilled beams are usually not considered radiant heating or cooling. Within this category, it is practical to distinguish between high temperature radiant heating, and radiant heating or cooling with more moderate source temperatures. This article mainly addresses radiant heating and cooling with moderate source temperatures, used to heat or cool indoor environments. Moderate temperature radiant heating and cooling is usually composed of relatively large surfaces that are internally heated or cooled using hydronic or electrical sources. For high temperature indoor or outdoor radiant heating, see: Infrared heater. For snow melt applications see: Snowmelt system.
The liquid droplet radiator (LDR) or previously termed liquid droplet stream radiator is a proposed lightweight radiator for the dissipation of waste heat generated by power plants, propulsion or spacecraft systems in space.
Integrated Science Instrument Module (ISIM) is a component of the James Webb Space Telescope, a large international infrared space telescope launched on 25 December 2021. ISIM is the heart of the JWST, and holds the main science payload which includes four science instruments and the fine guidance sensor.
The spacecraft bus is a carbon fibre box that houses systems of the telescope and so is the primary support element of the James Webb Space Telescope, launched on 25 December 2021. It hosts a multitude of computing, communication, propulsion, and structural components. The other three elements of the JWST are the Optical Telescope Element (OTE), the Integrated Science Instrument Module (ISIM) and the sunshield. Region 3 of ISIM is also inside the spacecraft bus. Region 3 includes the ISIM Command and Data Handling subsystem and the Mid-Infrared Instrument (MIRI) cryocooler.