AérospatialULB

Troubleshooting and redesign of a vibration isolator for Space Truss (ESA-ULB-MicroMega)

Dec.2002 – Aug.2003, Research Engineer, Département des constructions mécaniques et robotiques, Active Structure Laboratory, UNIVERSITY OF BRUSSELS (BRUSSELS, Belgium)

Description:

For the European Space Agency (ESA), MicroMegaDynamics and ULB were developing an active control vibration isolator based on the so called Stewart Platform: a specific 6 degrees of freedom positioning device.

This vibration isolator is intended to be installed between the structural truss of a satellite and high precision measuring systems, typically laser metrology or telescopes, typically used for inter-satellite optical/laser communication or to observe stellar objects in the deep/early universe.

The noise sources onboard a satellite typically come from reaction positioning wheels, stepping motors, cryocoolers, thermal ‘crinkling’, optics motion, micro-thrusters, Field-Emission Electric Propulsion propellers.

ULB developed and built such Stewart platform BUT some undesired side-effects badly perturbed the expected dynamic isolation behavior of the structure.

I knew the CEO of MicroMegaDynamics, Nicolas Loix, and after some discussions together, I accepted to lead the team trying to get rid of those problems, bringing my knowledge and competences learnt at LMS.

 

The problem were solved by:

  • building a few experimental test benches to measure with laser beams the real dynamic behavior of each element of the assembly and of the whole assembly,

  • Building an accurate Finite element model (SAMCEF) of each element and of the entire assembly

  • Updating the FEM so that the theoretical behavior perfectly matches the reality

  • Accurately understanding the parasitic behaviors: the lateral stiffness of the membrane of the actuators needed to be improved with a decrease of the axial stiffness, and very important, the joints between the actuators and the platform needed to be stronger and with the least stiffness.

 

  • by use of the FEM and a matlab program, optimize those critical elements with design for experiment with a fully parametrized calculation chain.

Results:

  • proposed a new design for the membrane and for the joints, with a specific super elastic material, the NiTiNol, developed by NASA as as Shape Memory Alloy:
  • Construction of the new membrane and of the new joint,
  • Tested and validated the parasitic behavior disappeared.

 

Responsibilities:

  • Technical lead of a 4 people team to resolve the issue, team work coordination within the department and with the client
  • Experimental analysis, FE modelling and FEM updating,
  • Calculation chain and design optimisation
  • Follow-up of suppliers, construction and validation of the modified prototype