Attitude, Orbit, Guidance, Navigation Control (AOGNC)

The AOGNC domain in a CDF study will mostly use COMET to design and model their equipment for the spacecraft. The following steps use the example of a Reaction Wheel to be modelled in the Tutorial COMET model:

  1. Connect to Citrix and open the COMET Application. To do so, follow the steps outlined here.

  2. Connect to the CDF COMET server and open the model Tutorial COMET. To do so, follow the steps outlined here.

  3. Also open the model AOGNC catalogue. To do so, follow the steps outlined here.

  4. Open the Element Defintion browser for both the Study Model and the Catalogue Model. You can do that by following the steps outlined here.

  5. Use the Generic Equipment from the catalogue to define the Reaction Wheel Element Definition in the Tutorial COMET model. To do so, follow the steps outlined here.

    NOTE: Normally, the Catalogue Model should first be searched to see if there already is an Element Definition describing the equipment in question. In this case, it is assumed this was done and no matching Reaction Wheel equipment was found. Therefore, this tutorial makes use of the Generic Equipment

  6. Use the Reference Data Library to add the additional parameter torque to the Element Definition. To do so, follow the steps outlined here.

  7. Populate the Manual fields of the Parameter Values for the parameters mass, maturity margin, power while on and the newly created torque parameter. To do so, follow the steps outlined here.

  8. Create 4 Element Usages of the Reaction Wheel in the Spacecraft Element Definition. To do so, follow the steps outlined here.

  9. The tutorial model contains 2 Options: the “Default” Option describing the baseline spacecraft design and the “Expanded” Option describing a larger version of the spacecraft with a larger payload. This requires some changes in the AOGNC design:
    1. The Reaction Wheel in the “Expanded Option” should have a larger torque and therefore this parameter needs to be Option dependent. To do so, follow the steps outlined here.
    2. Introduce different values for the torque parameter in the two Options.
    3. The “Expanded Option” will also require a 5th Reaction Wheel inside the Spacecraft which is not necessary in the “Default” Option. To do so, follow the steps outlined here.
  10. Creating a power budget in COMET requires the use of Finite States modelling the system modes of the spacecraft. In this tutorial model only two system modes are defined as Finite States: the Safe Mode and the Operational Mode. To model the varying power consumption of the Reaction Wheel during both modes:
    1. Introduce State Dependence to the parameter power duty cycle of the Reaction Wheel. To do so, follow the steps outlined here.
    2. Populate the power duty cycle parameter by providing values for the different Finite States.

Example Equipment - AOGNC

In the above steps the COMET Application was used to directly interact with the Study Model. However, one of the key advantages of storing data on the COMET server is that it also offers the possibility to interact with the Study Model using standard Excel workbooks and using the COMET server as an interface between the workbooks of the different domains. In the following steps, an overview on how this link between the Study Model and Excel can be achieved with the Excel COMET Plugin is provided. A specific Excel workbook for the AOGNC domain has been set-up by the AOGNC experts from previous CDF studies and should be available in the Study Folder of the CDF Working drive (accessible from Citrix). In this tutorial, for the sake of simplicity, a blank Excel workbook will be used to demonstrate the basic functionality:

  1. Use the COMET Application to subscribe to the parameter wet mass of the Spacecraft Element Definition. To do so, follow the steps outlined here. This parameter will be needed for the Excel computations.

  2. Connect to Citrix and open an instance of Excel with the COMET Excel Plugin. To do so, follow the steps outlined here.

  3. In Excel use the COMET Excel Plugin to connect to the CDF COMET server and open the model Tutorial COMET. To do so, follow the steps outlined here.

  4. Execute a Rebuild and find the wet mass parameter Actual Value cell in the Parameters sheet. To do so, follow the steps outlined here.

  5. On a new sheet in the Excel workbook perform a simplified calculation to compute a value for the mass parameter of the Reaction Wheel making use of the cell name referring to the Subscription of the wet mass parameter. To do so, follow the steps outlined here.

  6. Attribute a cell name to the result field including the calculated mass parameter. To do so, follow the steps outlined here.

  7. In the Parameters sheet insert the cell name as a formula in the Computed field of the mass parameter and set the Switch accordingly. To do so, follow the steps outlined here.

  8. Use Submit to “push” the computed value to the Study Model. To do so, follow the steps outlined here.

  9. Switch back to the COMET Application and verify the new value is introduced in the mass parameter and marked as ready for publication (highlighted in blue).