## 3 Background
### Thermal System Overview  
All components inserted into the CubeSat design have a range of operating temperatures, and a survival range, which if exceeded, will cause failure of the component. It is, therefore, vital the temperature throughout the CubeSat is managed using a range of thermal devices. A passive thermal control system is defined as one which does not require power input from the electrical system. Passive systems are typically low cost, risk, weight, and volume with high reliability [7]. Passive systems usually comprise of Multi-Layered Insulation and specially developed  
Figure 23: Solar Sail Attached to a 3U CubeSat in Orbit [40]. Figure 24: Stowed vs. Deployed Solar Sail Configuration [40]. surface coatings manufactured by companies such as 3 M, and occasionally additional systems including heat pipes and sunshades [23]. MLI and thermal coatings have been integrated upon many notable CubeSat craft including COMPASS-1 and PICARD [2]. Thermal insulation is incorporated into CubeSat design to block incoming solar radiation, and to prevent excessive heat dissipation. It is commonly applied to maintain a set temperature range for on-board electronic equipment during orbit. The commonest form of thermal insulation is the Multi-Layer Insulation Blanket. MLI Is suited to small craft (Figure 25), where it is compressed as this drastically increases performance. Care must be taken when attaching MLI blankets, as performance drops drastically as size decreases [23]. Surface coatings are a more ideal alternative to MLI blankets for CubeSats as it is a less delicate system, and easier to incorporate into the P-POD dimensions. MLI Blankets are not necessary for faces which are not incident with solar radiation, as a coating would offer the same performance occupying less volume and reducing cost. Silver tape presents an excellent radiator as it can reflect solar heat effectively [42]. Thermal straps allow passive heat transfer to a thermal sink. Standards components are widely available constructed from thin aluminum or copper foil layers as these materials are strong thermal conductors. This heat sink then dissipates heat safely away from critical temperature components. Heat straps are ideal for cooling components exposed to solar radiation. Heat pipes are an efficient solution for passive heat transfer inside a CubeSat system. A closed loop system transfers heat via temperature gradients [23]. Heat transfer usually occurs from electrical components to cold radiator surfaces. Heat pipes can be circular or flat and are commonly constructed from steel tubing placed between aluminum plates alongside a working fluid. A range of active power-consuming systems are available for the CubeSat platform, delivering a higher precision and more effective heat transfer solution than equivalent passive systems [6] Active systems are usually integrated when passive systems cannot adequately control temperature. Actively controlled thermal straps are capable of impressive heat dissipation and cooling. The load path aerospace structures organization have developed a strap capable of 50 Wcm\({}^{-2}\) dissipation and cooling capacity of 35 W [43] Heaters have been used on several notable CubeSat missions including Compass-1 [23]. Heaters are typically used to maintain a safe battery temperature and are usually active during the eclipse phase controlled by a thermostat. Figure 25: MLI Blanket Incorporated Satellite in Orbit [41]. Cryo-coolers, Figure 26 are usually implemented to extremely temperature sensitive devices such as infra-red sensors [23]. A specially developed tank is required to store the coolant making this solution suited to larger craft of dimensions 3U and above. In 2016 the Cryo-Cube-1 was the first craft to test a cryo-cooler system [44]. The future of active thermal control systems may lie with Thermotive's Pyrovo Pyrolytic graphite film thermal straps. This design incorporates Pyrolytic graphite wrapped in an aluminized Mylar blanket.