Spacecraft Model Based System Testing – Correlation of Test & Simulation

In 2019, the three Radarsat Constellation Mission (RCM) satellites were successfully launched into orbit. These satellites demonstrate the benefits of a seamless collaboration of simulation and test for complex space systems.

Using the example of the Falcon 9 satellite, the paper, Spacecraft Model Based System Testing – Correlation of Test & Simulation, Maya HTT presented at IMAC XXXIX, shows how modal simulation is used to prepare the test and how simulation can achieve more productive and realistic testing. Test-simulation correlation deals with four main challenges:

  • How to be sure the analysis model is accurate
  • How to prescribe a cost-effective test
  • How to compare FEM and test, qualitatively and quantitatively
  • How to update the FEM to match reality

How well does a Finite Element (FE) model of a spacecraft represent reality?

One way to find out is to perform modal testing and to compare, or correlate, the test and simulation results.

This is particularly important in the space industry, as launch loads are derived from validated models of the launch vehicles and the spacecraft. A poor model means uncertain loads and increased program risk.

Before performing a modal test, requirements must be defined and the required modes clearly identified. How many sensors and exciters are required? Where are they located, and in which directions do they point? For test engineers to visualize test mode shapes, a wire frame mesh must connect the sensor and exciter nodes. Finally, the test article configuration and boundary conditions must be investigated.

What if the simulation and test results did not correlate properly?

Test and simulation FRFs and mode shapes are compared based on quantitative and qualitative tools (MAC, MODMAC and Orthogonality). Once correlation establishes the differences between both representations, the FE model must be updated to more accurately represent reality.

Updating the FE model is done based on an optimizer, which can handle large numbers of variables (physical and material properties). However, in the case of the RCM satellites, the update is complicated by the test boundary conditions, in which the spacecraft was bolted to a concrete floor. We attempted to account for the flexibility of the interface plate and for the effect of the floor and of the underlying soil in the updating process.

Multi-discipline analyses are then performed on the updated FE model to validate the design against specific loading conditions (acoustic, vibro-acoustic, dynamics, etc.).

To learn more about the challenges of the modal simulation-test interaction in simulating space systems and how a fully integrated workflow can reduce iteration-engineering loops and improve simulation-test interactions, contact a Maya HTT expert.

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