  An increasing number of blazars have been reported to show jet wobbling
(i.e., non-regular rotations of the structural position angle of their
innermost jets in the plane of the sky with amplitudes between 20 deg. and 50
deg., and time scales between 2 yr. and 20 yr.). The physical origin for the
observed jet wobbling is still poorly understood, but as this phenomenon is
triggered in the innermost regions of the jets, it must be tied to fundamental
properties of the inner regions of the accretion system. Thus, jet wobbling may
be an interesting potential tool for supermassive black hole, accretion and jet
launching studies. As part of a joint theoretical/numerical and observational
effort to characterize the observational properties and differences between
these three possible scenarios we have started a long-term polarimetric
phase-reference 43 GHz VLBA monitoring program to observe the jet structure and
the absolute motion of the jet core of four of the blazars which have shown
some of the clearest evidence of large amplitude jet wobbling: NRAO 150, OJ
287, 3C 273, and 3C 345 . Here we present this project and we argue about its
suitability for future VSOP-2 observations.
