Spacecraft thermal control

The temperature control system or thermal control system of a satellite or spacecraft is any technical systems and control measures, control and regulate the temperature on board in all phases of flight.

Since a spacecraft is exposed to the vacuum of space, a recording and mainly supply energy in the form of heat to the surroundings by conduction is not possible. This is one of the essential factors that must be taken into account already in the design of a satellite as this is the temperature (or better to the upcoming thermal equilibrium ) of a satellite can be controlled only by irradiation and radiation (see also Gray or black body ). In order to prevent that some parts of the systems and the satellite or the entire satellite overheating or freezing, a careful planning and control is necessary. Depending on the nature of the spacecraft (extremely between the sun and deep space probe ) are necessary partly extensive measures to prevent consumption or generation of heat or loss thereof.

Influencing the temperature

To influence the temperature of a spacecraft or its systems it is only possible to change one of the following sizes:

• Heat supply: From the outside receptacle ( absorption ) of the radiation from the sun, or other celestial bodies nearby,
• From inside: waste heat from on-board equipment (dissipation )

It is possible to control by means of the following measures:

• Passive: on the surface properties (coating, polishing, roughening ), thermal insulation, heat shield (eg gold foils), blinds or shutters, heat-conducting materials, surface geometry
• Semi- passive: on phase transformation (eg, heat pipe ), Bimetallschuppen
• Active: about heating elements, cooling circuits, air conditioners (especially manned satellites), orientation of the satellite

Target of temperature control is to keep the components within the intended temperature range for storage and operation, and optionally a suitable temperature for a human crew.

The typical allowable operating temperatures from satellite components differ and are used in chemical processes for engines from 10 to 120 ° C in tanks at 10 to 40 ° C ( Einstofftanks ), in the case of batteries at -10 to 25 ° C, for electrical components for transponders 10 to 45 ° C, earth sensors at -10 ° to 55 ° and mechanical components in momentum wheels at 0 to 45 ° C and at antennas at -170 to 90 ° C.

Theoretical model of temperature change

To avoid that individual components suddenly stop in its intended temperature range are (overheating, freezing ), simulations are carried out. In this case the satellite is called node (as assumed isothermal sections ) is divided exchanging with each other and with the environment heat. For each of these nodes, the heat exchange variables are added.

If the satellite is in thermal equilibrium ( ie no longer be heated or cooled, and thus the change in the temperature goes to zero ), the following applies:

Where P is the power, m is the mass and heat capacity.

In many cases, these numerical simulations are supplemented or completed by tests. For this, find thermal vacuum chambers, possibly with solar simulation, using.

The temperature development of the individual components of a satellite in near Earth be influenced by the following factors:

Heat absorption

Heat can be absorbed by the following sources:

• Solar radiation:

• Albedo ( sunlight reflected from the Earth ):

• Geothermal energy:

• Space radiation:

• Dissipation:
• Aerodynamic heating: For very terrestrial planets or near railways also an absorption of energy by friction at the Earth's atmosphere has to be considered ( aerodynamic heating ) possible and with.

Heat transfer to other components

Heat transfer to other parts of the spacecraft can be effected by:

• Convection
• Heat conduction
• Heat radiation

Heat dissipation into space

The only way to heat in space to release it again, is the radiation into space:

Mostly for special radiators are used, which then may not be exposed to sunlight. For sun near missions it may be necessary to tune the whole satellite design on the design of the radiating surfaces.