  Three dimensional (3D) adaptive-mesh refinement (AMR) hydrodynamical
simulations of the wind-wind collision between the enigmatic super-massive star
\etacar and its mysterious companion star are presented which include radiative
driving of the stellar winds, gravity, optically-thin radiative cooling, and
orbital motion. Simulations with static stars with a periastron passage
separation reveal that the preshock companion star's wind speed is sufficiently
reduced that radiative cooling in the postshock gas becomes important,
permitting the runaway growth of non-linear thin shell (NTSI) instabilities
which massively distort the WCR. However, large-scale simulations which include
the orbital motion of the stars, show that orbital motion reduces the impact of
radiative inhibition, and thus increases the acquired preshock velocities. As
such, the postshock gas temperature and cooling time see a commensurate
increase, and sufficient gas pressure is preserved to stabilize the WCR against
catastrophic instability growth. We then compute synthetic X-ray spectra and
lightcurves and find that, compared to previous models, the X-ray spectra agree
much better with {\it XMM-Newton} observations just prior to periastron. The
narrow width of the 2009 X-ray minimum can also be reproduced. However, the
models fail to reproduce the extended X-ray mimimum from previous cycles. We
conclude that the key to explaining the extended X-ray minimum is the rate of
cooling of the companion star's postshock wind. If cooling is rapid then
powerful NTSIs will heavily disrupt the WCR. Radiative inhibition of the
companion star's preshock wind, albeit with a stronger radiation-wind coupling
than explored in this work, could be an effective trigger.
