  In two previous papers we presented the LARES 2 space experiment aimed at a
very accurate test of frame-dragging and at other tests of fundamental physics
and measurements of space geodesy and geodynamics. We presented the error
sources of the LARES 2 experiment, its error budget and Monte Carlo simulations
and covariance analyses confirming an accuracy of a few parts in one thousand
in the test of frame-dragging. Here we discuss the impact of the orbital
perturbation known as the de Sitter effect, or geodetic precession, in the
error budget of the LARES 2 frame-dragging experiment. We show that the
uncertainty in the de Sitter effect has a negligible impact in the final error
budget because of the very accurate results now available for the test of the
de Sitter precession and because of its very nature. The total error budget in
the LARES 2 test of frame-dragging remains at a level of the order of 0.2%, as
determined in the first two papers of this series.
