# Thermal Control of CubeSat Electronics Using Thermoelectrics
## 1 Introduction  
Thermal management is becoming a critical issue for advanced low-Earth orbit (LEO) small satellite (SmallSat) missions. However, it is one whose significance is often overlooked. This is despite the number of launched SmallSats rising considerably to >1000 per year--an order of magnitude increase over the past decade and a trend that is predicted to grow [1]. Future advanced SmallSat services, such as Earth Observation, Space Situational Awareness and Next Generation Satellite Communications (NextGenSatCom), will require increasing onboard computational power, something that will generate more heat, which must be managed [2]. A CubeSat is a class of SmallSat, built in cubic units of approximately 0.1 m \(\times\) 0.1 m \(\times\) 0.1 m, with each cube weighing approximately 1 kg. CubeSats are typically in the 1 U to 6 U range and are often assembled using off-the-shelf componentty. CubeSats often rely on the (emissivity/absorptivity) properties of their external surfaces, in combination with orbit attitude, to ensure that on-board electronics and/or other heat-sensitive components remain within the manufacturer's recommended temperature range--the maximum operating temperature being ordinarily between 85 \({}^{\circ}\)C and 120 \({}^{\circ}\)C [3, 4]. The reliability of space electronics is critical and this is closely related to operating temperature. Studies have shown that reliability decreases by 50% for every 10 \({}^{\circ}\)C increase in operating temperature [5]. [PERSON] [6] found that for every 1 \({}^{\circ}\)C decrease in the temperature of electronic chips, the failure rate of the electronic chips would decrease by about 4%. Similarly, even if the electronic chips are not damaged at elevated temperature, their life span is shortened significantly [7]. Deployable radiators can be used to dissipate larger amounts of heat, however, their use can add significant additional complexity and a greater risk of mission failure, should they unsuccessfully deploy. Likewise, their surface area is often limited [2]. It is possible to aid the performance of standard, body-mounted radiators by minimizing the thermal resistance between the heat-generating electronics and the radiators. This can be achieved by a number of methods, usually defined as either passive or active systems. Passive systems are often the preferred solution since they offer advantages in terms of simplicity, cost, mass, volume, as well as requiring no electrical power. Heat pipes are the most common heat transfer device used on SmallSats [2]. They consist of a metal pipe that holds a liquid under pressure and a wick. When one end of the pipe is heated the liquid at that end vaporizes and moves to the cooler end where it condenses and is transported back to the other end by wicking, for the cycle to repeat. This method is effective, but its use of a liquid can lead to catastrophic failure if a leak occurs. The same issue is applicable to passive systems employing phase change materials for thermal management. The major drawback for active systems is their added complexity and a reliance on input power for operation. They have however been shown to offer tight temperature control, to cool below ambient temperatures, and offer the potential for higher-performance cooling [2]. Ultimately, the choice of thermal management technology and whether to employ a passive or active system, is often a trade-off between performance benefits and the additional costs (time, risk, financial) associated with development. Thermoelectric modules are one category of active thermal management device. They exploit the Peltier effect to create a heat flux at the junction of two different types of materials. A thermoelectric cooler is effectively a solid-state heat pump that rejects heat from one side of the module to the other, while consuming electrical energy. Thermoelectric modules have found a variety of applications terrestrially.