Cryocoolers are refrigerators that are designed to reach cryogenic temperatures (-130  ). They are designed in tabletop sizes and have an input power of less than 20 kW. 

A cryogenic refrigerator has four major components:

• Compressor
• Heat exchanger
• Expansion device
• Evaporator

In the first stage, the gas gets compressed and goes to the heat exchanger. Here any residual heat from the gas is removed and is expanded due to a sudden drop in the pressure or lack of compression. The expansion device then expands the gas furthermore which results in the formation of a cryogenic liquid due to the process of condensation. The cryogenic liquid is used to keep the objects cool for their intended purposes. The liquid is then subjected to the evaporator where the temperature and the pressure are increased substantially. The increased temperature and pressure result in the formation of gas from the cryogenic liquid as a result of evaporation which is then redirected again to the compressor where the whole process repeats itself. This whole process takes place in a close cycle manner, which means the mass of the working gas throughout all stages is kept constant.

Initially, a cryogen (liquid nitrogen or liquid helium) was required to keep an object under subzero temperatures and they were expensive to procure as well. However, with the introduction of cryocoolers, cryogens are not required anymore. Cryocoolers are low maintenance, reliable, and comparatively cheap. They are usually lightweight and have a small volume. Cryocoolers have a rapid cool-down time and offer a vibrationless operation. Additionally, cryocoolers have a long shelf life.

Sensors and lenses attached to a satellite or a space telescope require extremely cold temperatures to function. However, in space, unadulterated sunlight can substantially increase the overall temperature of these sensors which might cause them to not function efficiently. Hence, cryocoolers are used in space to keep sensors and lenses extremely cold and functional so that satellites and space telescopes can take the reading & pictures required.

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