  We have used the Very Large Array (VLA) at 7 mm wavelength to image five
rotational transitions (J=1-0) from three SiO isotopologues towards Orion
BN/KL: 28SiO v=0,1,2; and 29SiO and 30SiO v=0. For the first time, we have
mapped the 29SiO and 30SiO J=1-0 emission, established the maser nature of the
emission, and confirmed association with the deeply embedded high-mass young
stellar object commonly denoted radio Source I. The 28SiO v=0 maser emission
shows a bipolar structure that extends over ~700 AU along a northeast-southwest
axis, and we propose that it traces a bipolar outflow driven by Source I. The
high-brightness isotopic SiO maser emission imaged with a ~0.2 arcsec
resolution has a more compact distribution, generally similar to that of the
28SiO v=1,2 emission, and it probably traces bulk gas flows in a region of
diameter <100 AU centered on Source I. On small scales of <10 AU, however,
compact 29SiO/30SiO v=0 and 28SiO v=1,2 emission features may be offset from
one another in position and line-of-sight velocity.
  From a radiative transfer analysis based on a large velocity gradient (LVG)
pumping model, we derive similar temperatures and densities for the optimum
excitation of both 29SiO/30SiO v=0 and 28SiO v=1,2 masers, significantly higher
than required for 28SiO v=0 maser excitation. In order to account for the
small-scale differences among the isotopologues (v=0) and the main species
(v=1,2), follow-up radiative transfer modeling that incorporates non-local line
overlap among transitions of all SiO isotopic species may be required.
