An interface between the MBSE tool OCDT and the thermal analysis software Thermisol is proposed. Goal of this new interface is to automate and accelerate iteration cycles within early mission design studies, following the new space approach.
ESA - European Space Agency
MBSE - Model Based system engineering
OCDT - Open Concurrent Design Tool
S/C - Spacecraft
TCS - Thermal Control System
TMM - Thermal mathematical model
TROPICS - TheRmal OCDT Parameter InterfaCe Script
In the framework of phase 0 and A studies, the concurrent design approach has become state of the art within the European space industry. The design philosophy of this concept is based on fast iterations and decision making of all subsystems. ESA applies this approach for phase-0/A studies at the Concurrent Design Facility (CDF). These fast iterations require a dedicated tool for data exchange among the responsible subsystem experts, the system engineers and the customer. An open-source tool which fulfils this purpose is OCDT, which is used and developed by ESA. This data model is used to exchange and store parameters, which describe the spacecraft’s specification for every subsystem and high-level mission information. Such parameters are for example mass, mode-depending power consumption and temperature limits.
The thermal subsystem has various interfaces to all other subsystems of a spacecraft and therefore strongly relies on their inputs during an early design phase. On the other hand, the power subsystem requires inputs from the TCS. All these corresponding parameters can be modelled and exchanged by using OCDT.
The TROPICS interface enables the user to generate a simple TMM directly from system model and to perform first design calculations like radiator and heater sizing by extracting relevant data from OCDT. This process is illustrated in the figure below.
In order to use TROPICS, the modelling of the S/C in OCDT must follow certain rules defined in a model methodology, which allows to ensure the connection and correct interpretation of the model-data by the TROPICS interface. This methodology is designed to not restrict the S/C model in OCDT to other modelling aspects.
The model philosophy introduces a parameter called “thermal node” on the 4th level of the OCDT model, also known as the equipment level. This parameter is used to collect physical parameters (heat capacity, dissipation, ...) and map them to the nodes of the TMM, which forms the common ground for both models. The TROPICS interface then uses these nodes to semi-automatically setup up a thermal mathematical model in Thermisol, to perform basic thermal design calculations. Subsequent design iterations can be computed based on the above described model setup.
Having the task of setting up a simple TMM performed early in a study allows to prepone the study model iterations including the thermal subsystem. This accelerates the design process by having early and fast iterated thermal design parameters.
The thermal subsystem specialist of an early mission study is now able to react fast to changes in the system and to communicate the impact on the TCS back to the other subsystem specialists and the system engineers by transferring the Thermisol results directly back into OCDT. “What-if” scenarios can be performed without implementing major changes to an extensive TMM.