Electrostatic charging of test masses in Equivalence Principle experiments in low-Earth, near-polar orbits Original Research Article

Experiments to test the Equivalence Principle in space are typically suggested for flight in low-Earth, circular, Sun-synchronous orbits at 400–600 km altitude. In these orbits the spacecraft routinely traverses the South Atlantic Anomaly (SAA), where the fluxes of trapped charged particles are enhanced. These particles, together with energetic solar flare protons and galactic cosmic rays, will penetrate the spacecraft structure and develop into a shower of lower energy particles which deposit electrical charge, energy (heat), and momentum on the test masses. Of these, charge leads to the most serious disturbances. Estimates of the charging rates have been computed using the GEANT radiation transport code, in conjunction with realistic proton flux models.