  High angular resolution imaging is an increasingly important capability in
contemporary astrophysics. Of particular relevance to emerging fields such as
the characterisation of exoplanetary systems, imaging at the required spatial
scales and contrast levels results in forbidding challenges in the correction
of atmospheric phase errors, which in turn drives demanding requirements for
precise wavefront sensing. Asgard is the next-generation instrument suite at
the European Southern Observatory's Very Large Telescope Interferometer (VLTI),
targeting advances in sensitivity, spectral resolution and nulling
interferometry. In this paper, we describe the requirements and designs of
three core modules: Heimdallr, a beam combiner for fringe tracking, low order
wavefront correction and visibility science; Baldr, a Zernike wavefront sensor
to correct high order atmospheric aberrations; and Solarstein, an alignment and
calibration unit. In addition, we draw generalisable insights for designing
such system and discuss integration plans.
