Spacecraft radiators are dedicated surfaces designed to dissipate excess heat through radiative transfer. Their properties are defined by both solar absorptivity and infrared emittivity – qualities which a spacecraft radiator must possess in order to operate effectively.
Paints, coatings and tapes can be used to alter the surface properties of spacecraft. SmallSats with limited surface areas require special thermal control structures.
Thermal Conductivity
Thermal conductivity of radiators determines their efficiency at rejecting spacecraft’s dissipated power, with higher conductivities providing more effective rejection while reducing their weight and cost. Materials with both high and low thermal conductivities are used in spacecraft components and thermal control systems – including louvres, thermal straps, sunshades, copper layers on circuit boards, interface conductance materials and thermal paints and coatings – to increase or decrease efficiency accordingly.
Spacecraft radiators are generally designed to radiate on both sides, though only one may be exposed during certain missions. Radiator temperatures can also be managed passively using passive thermal management techniques – this technology requires lower mass, volume and risk than powered equipment and can be especially helpful for SmallSats with limited launch resources. Examples of passive thermal control techniques are MLI, coatings/surface finishes thermal straps as well as maintaining specific orientation for science operations – although their capacity and suitability depend upon mission type and temperature limitations may limit their usage as they may not suit every mission type perfectly!
Emissivity
Spacecraft radiators are dedicated surfaces used for dissipating heat through radiative transfer. Their primary characteristics are low solar absorptivity and high IR emissivity – often referred to as their “radiator properties”. Radiators should typically be stored during transit or when not needed, and deployed when electronics waste heat levels rise.
Spacecraft equipment generates waste heat at various rates and temperatures. To prevent increases in spacecraft temperatures from occurring, this waste heat must be eliminated through various means; radiators are one effective means but must be activated when required.
Switchable radiators offer spacecraft the advantage of reduced mass and power requirements by only activating when necessary. Their performance can be assessed through direct emitted power measurements (considering both normal and hemispherical emissivity). These measurements are then compared with near-normal optical measurements which do not take into account angular dependence in their measurement process.
Rejection Temperature
Spacecraft power systems and components generate heat that must be dissipated to avoid overheating. The heat generated from these components is dispersed into a coolant that circulates within the spacecraft before being transferred out through pumps or transported directly to radiator panels located outside. Once there, these radiator panels then release their heat through thermal radiation into space environment, dispersing its effects evenly throughout space.
Radiators’ ability to reject heat depends on their rejection temperature, which must exceed that of their ambient environment for it to work effectively. Furthermore, radiators have fixed sizes which limit how much heat they can reject over time. When spacecraft temperatures near their lower permissible limit for radiation rejection, survival heaters must be used to keep equipment operating temperatures steady; this additional power consumption reduces propellant available for acceleration; therefore advanced TCS technology must be developed so as to maximize energy efficiency and resilience even at lower temperatures.
Louvers
PCM provides the opportunity to reduce mass for passive thermal management systems that could serve in place of heaters, such as PCM radiators. A heater requires constant power consumption as well as complex data and command lines to track its temperature control over time.
Spacecraft designers rely on thermal blankets to retain and regulate internally generated waste heat, thus avoiding overheating and protecting structural and electronic equipment from micrometeorites.
The Europa Clipper spacecraft contains eight large louvers mounted to its radiator panel that open during hot environments to dissipate excess heat into space and close when temperatures decline – helping keep power consumption within its allowable flight temperatures for efficient operations.