Thermal Desktop model

93

Copper 0,64 0,15

Solder mask blue 0,7 0,88

Steel 1 0,70

Table 9: ESA-uProp 3 model - Optical properties

During the study of the possible solutions for the thermal protection of the critical systems of the platform, components with materials different from those used in the previous version of the project were used in the analysis. The innovations concern the electronic boards in aluminium, which have been the subject of study as they are characterized by a better heat conductivity, and therefore greater ease of heat

dissipation compared to the classic FR4 avionic boards. The other novelty was the use of thermal pads with the gap filler function that allows to fill the air gap between uneven surfaces. Thermal gap pads provide a thermal interface between heatsinks and electronic devices. As can be seen from the table of thermophysical properties, the performances of the Gap Filler 707-4597 were analysed, as it is already available in the laboratory, and a generic gap filler, to which the parameters of thermal conductivity and thickness were changed during the various simulations, in order to simulate the different thermal pad solutions on the market. There are no optical properties of the gap fillers as they are located in the centre of a sandwich structure between the electronic boards and the panels of the structure.

94 data collected regarding other ePS models, even if often not very detailed.

Furthermore, it is considered that reaching high propulsive powers should increase the efficiency of the propulsion systems, therefore the efficiency value considered is a conservative estimate downwards of those actually found on the ePS that will be tested.

Figure 44: ePS integrated in CTP structure

Subsequently, the two battery packs of the CTP were integrated with the

propulsion system, including their respective battery drawers. The modelling of these components was based on those already implemented on the 6U platform. In fact, in terms of size, each battery pack is similar to that present in the previous version of the model. They are assembled on the + X and + Y sides of the service module, one

connected to the + Z panel and the other to the -Z one. Compared to version 2 of ESA-uProp, therefore, the battery packs have been doubled, effectively doubling the availability of electricity that can be stored on board, and both use the same type of batteries. Since the performance of the latter has not yet been defined, during the thermal analyses the thermal power dissipated by the batteries will be a variable parameter.

95

Figure 45: integration of battery packs on-board CTP

Finally, the avionics module of the CTP was modelled, including a volume of 2U.

Compared to the previous version of the platform, this is the part that has undergone the most changes. The electronic boards are no longer assembled vertically one above the other to occupy 1U of volume, but are divided into two distinct series, and

arranged horizontally between them. To model the structural support that holds them in place, the cylindrical solid element was again used, already used in the previous model to model the four support bars for avionics. These supporting structural

elements have been connected at one end to the structural panel + X, and at the other to the bulkhead that separates the service module from the propulsion module.

The two electronic boards positioned in + Z and in series with each other are those belonging to the EPIS system, and are respectively the EPIS power and the Data Logger.

The first has the function of power interface towards the propulsion system, regulating the input voltage to the ePS through the DCDC step-up circuit component, while the DL is responsible for the communication, data and command interface towards the ePS.

Three electronic boards are positioned in series on the -Z side: EPS, CDH and COMSYS. The first manages the electrical energy on board, acting as an interface with the batteries, with external energy sources and with the EPIS power system. It also supplies electricity to the other CDH and COMSYS avionics boards via the 5V and 3.3V power buses. The CDH and COMSYS boards with regard to thermal modelling are similar to the respective ones implemented in the 6U model of ESA-uProp 2.

96

Figure 46: Avionics boards disposition

Figure 47: Avionics module integration

97 As explained in detail below, the configuration of the avionics module is not

uniquely defined, but is changed during the thermal analysis campaign.

In the next sections dedicated to thermal analysis and the design of the thermal control system, the boards responsible for the electrical management on board the CTP will be of particular interest: EPS and EPIS power.

These two electronic components, due to the high electrical power required for the operation of the ePS and the other electronic elements, are responsible, together with the ePS itself and the batteries, for the greatest heat dissipation on board the CTP.

Therefore, their modelling requires high detail and precision, in order to study their thermal performance as accurately as possible, and how to adequately protect them from the high temperatures reached by their components.