Functional modelling with subsystems

Table of Contents

All models will contain some Element Definitions which describe the Spacecraft Subsystems as a whole. These Element Definitions, following ECSS modelling standards, represent the functional respresentation of a subsystem. They are therefore not describing physical components, but the function of each subsystem is captured through them.

At the beggining of the CDF study, when the design of the Mission and the Spacecraft are not clear, these Element Definitions can be used to provide a mass and power estimate for a complete subsystem.

To add values to a subsystem:

  1. Locate the subsystem in the Element Definitions browser.

  2. Expand the subsystem.

  3. Fill in the three values in the Manual column.
    1. Mass = estimated total mass for entire subsystem.
    2. Maturity margin = 20% - assumed for functional subsystem level figures.
    3. Mean consumed power = estimated power consumption for entire subsystem.
  4. Check that in the Switch column the value is set to Manual.

Subsystem Functional Modelling

NOTE: When a value is changed on COMET, it turns blue , showing the system has registered the change.

Experts are expected to provide estimates for the mass, power and margin of their subsystem at the beginning of the study. These values do have to be provided with a very high level of confidence, they should represents best guess estimates. The iterative CDF process will ensure the solution converges over time.

Hide Example
At the beginning of the study the Power expert may not know anything specific about their equipment. However, with a few basic inputs from the Systems team, such as a first estimate on the total power consumption, what the likely orbit will be etc., the Power expert can make some first guesses about the total size of the power subsystem.

This corresponds to the Power expert filling in the mass, power and margin in the Power subsystem in COMET.

Functional power model


Each expert will do the same to create a first guess giving an order of magnitude for the mass and power. All these first guesses can then be combined into a Functional Representation of the spacecraft.

Spacecraft functional model


As the design will be iterated multiple times if the initial guesses are incorrect this is not a problem, as the results will converge to a solution across the iterations.