Populating equipment Parameter Values

Table of Contents

1. Maturity Margin
2. Power Duty Cycle
3. Redundancy Concept
4. Number of Items

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After the equipment has been created as Element Definitions, ensuring all the necessary parameters are included, it is important to start giving values to those parameters. In the scope of concurrent engineering, the values given to parameters owned by one domain can be useful for other domains and should therefore be kept up to date. At the beginning of the modelling exercise it may not be possible to provide accurate values for parameters due to the high uncertainties within the model. However, towards the end of the study, values should become more accurate as more calculations will be completed which will reduce the uncertainties within the model.

To deal with this reality, each parameter has a Manual, a Computed and a Reference field that can be filled in. In general:

Manual is for a value based on initial best guess at the beginning of the study. Later in the study, the value can also be filled with a value resulting from calculations.

Computed is for a value which resulted from an analysis or computation. This is typically closer to the final solution, as it is the result of some calculation, but is still expected to change as the overall design is iterated.

Reference: a value used for comparison that originates e.g. from a data sheet or a previous study.

⚠️ WARNING: The Computed value cannot be typed into COMET directly. It can only be populated by pushing it through external tools such as the COMET Excel Plugin (see here)

1. To assign a Parameter Value to a parameter, navigate to that parameter in the Element Definitions browser and fill in the value in the appropriate slot (Manual or Reference). Make sure that the Switch value is set to corresponding entry. Manual, Computed and Reference can all be populated with a value but, while they all remain visible to other domains, only the one indicated by the Switch will be published.

   

   NOTE: It is expected that all parameters are given a value where possible.

2. When assigning values to parameters, be careful to ensure the input value is in the correct units as indicated by the Scale.

3. There are four special parameters that are often used when modelling in COMET. These are tackled below.

Maturity Margin

The maturity margin is one of the 24 standard parameters and it reflects the design maturity of the equipment. In the CDF, it should be employed as specified in the CDF Standard Margin Philosophy (only accessible within ESA VPN) and it is advised to read this document prior a CDF study.

1. In general, the parameter takes the following values:

   	Maturity Margin	ECSS-E-ST-10-02C Product Category
   5%	For off-the-shelf equipment with no modifications	A
   10%	For off-the-shelf equipment with modifications	B or C
   20%	For newly designed and developed equipments	D

2. The parameter is populated normally, as any other parameter would be:

   

⚠️ WARNING: Do not confuse the maturity margin with the System Margin. The maturity margin is populated in each equipment by the experts. The System Margin is added by the systems team to the system as a whole, on top of the maturity of each equipment

Power Duty Cycle

The power duty cycle is one of the 24 standard parameters and it is closely related to the concept of Finite States, which is tackled here. This parameter describes the percentage of time the equipment is active during a given state. It can take the following values:

Value	Meaning
0 ≤ power duty cycle ≤ 1	A percentage of the time the equipment is consuming power during the given state. A value of 0 means the equipment is on Standby and does NOT mean the power consumed during the state is 0 W
-1	The equipment is off for the entire duration of the state and will consume 0 W of power

NOTE: The calculation of the mean consumed power, which is dependant on the power duty cycle, follows the (simplified) equation:
P_mean = [ P_on * DC + P_Stby * (1 - DC) ] * [ 1 + MM ]
where: P_mean is the mean consumed power, P_on is the power while on, DC is the power duty cycle, P_Stby is the power in standby and MM is the equipment maturity margin.

Values for the power duty cycle are applied as they would for any other parameter.

NOTE: The example of the Power expert modelling the solar array that has been used so far is not applicable here because the power duty cycle parameter does not apply to a solar array. For this reason, in the figure below, the power duty cycle has been applied by the Instruments expert to the payload equipment:

Redundancy Concept

The redundancy concept is one of the 23 standard parameters and it allows redundancy to be modelled in the system. It is composed of four sub-parameters:

Name	Value	Meaning
redundancy.scheme	active passive standby	hot redundancy - all units always on cold redundancy - k units on and n-k off k units on and n-k standby
redundancy.type	internal external	redundant units all in single package/box Only one Element Usage in COMET redundant units explicitly modelled in design n Element Usages in COMET
redundancy.k	integer >= 1	number of units needed for nominal operation
redundancy.n	integer > k	total number of units in the system

NOTE: The example of the Power expert modelling the solar array that has been used so far is not applicable here because the redundancy concept parameter does not apply to a solar array. For this reason, in the figure below, the redundancy concept has been applied by the Instruments expert to the payload equipment. In this case, the payload contains two identical components internally, both of which are always on but only one of which is required for nominal operation:

NOTE: For more in-depth information on the redundancy concept parameter, see the advanced section

Number of Items

Finally, the parameter n_items is used to model equipment which appears multiple times in the model. For example, if 2 identical solar arrays are required on the Spacecraft, the n_items parameter can be set to 2 in the Element Definition of the solar array. The mass and power parameters will be acconuted for n times when this parameter is used.

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Hide Example

The Power expert can now input values for the parameters in the blueprints. After this step, the Power expert has some very detailed and representative blueprints, ready to be added to the overall system.

This corresponds to adding values to parameters in all Element Definitions in COMET.