Study of the Interaction Between the ROSETTA Orbiter and the Cometary Plasma

ESA's Technology Research Programme; Ref. Contract 12398/97/NL/MV with CNRS/CETP (F) and ONERA (F) 1999

 

Introduction

This activity consists of a study of the equilibrium floating potential of the ROSETTA orbiter in the plasma and solar fluxes conditions that are expected during the ROSETTA mission. Numerical simulations have been used to model the plasma sheath surrounding the orbiter and the solar panels and to determine the floating potential of the spacecraft. Several cases with various distances of the orbiter to the comet nucleus and of the comet to the sun were modelled, first in a 2D approximation, then in a full 3D configuration.

The simulations were validated by ground experiments in the JONAS plasma facility at ONERA Toulouse in configurations as close as possible to flight configurations. Results of this study shows that the floating potential of the spacecraft will be several Volts positive in most situations, except in the nearest vicinity of the nucleus. This is a consequence of the photo-emission from the large sunlit area of the solar panels which needs a high positive potential to be counterbalanced by the collection of thermal electrons in a low density plasma. The consequence of this positive floating potential in a plasma with typical particle energies of a few tens of millieV at most is that plasma instruments and ion spectrometers onboard the ROSETTA orbiter may not be able to perform correct measurements of the plasma parameters and ion composition. Furthermore, the calibration of the instrument may turn very difficult without sophiticated 3D modelling. Some solutions to overcome these difficulties are proposed in conclusion.

 

Products & Information

The products expected to be delivered are:

  • Study report
  • Simulation results
  • Plasma chamber test results on mock-up

 

By-products

  • Comparison of numerical simulations using the ONERA code SILEX and plasma chamber tests which validated the code.
  • Proposal for a technique to minimize spacecraft potential perturbation on cold ion measurements.

 

Team

CNRS/CETP Jean-jacques Berthelier Technical manager and CNRS/CETP main contact
ONERA/DESP Jean-Francois Roussel ONERA/DESP main contact
ESTEC A. Hilgers Initiator and Technical officer