  Multi-messenger observations of the transient sky to detect cosmic explosions
and counterparts of gravitational wave mergers critically rely on orbiting
wide-FoV telescopes to cover the wide range of wavelengths where atmospheric
absorption and emission limit the use of ground facilities. Thanks to
continuing technological improvements, miniaturised space instruments operating
as distributed-aperture constellations are offering new capabilities for the
study of high energy transients to complement ageing existing satellites. In
this paper we characterise the performance of the upcoming joint SpIRIT +
HERMES-TP/SP nano-satellite constellation for the localisation of high-energy
transients through triangulation of signal arrival times. SpIRIT is an
Australian technology and science demonstrator satellite designed to operate in
a low-Earth Sun-synchronous Polar orbit that will augment the science
operations for the equatorial HERMES-TP/SP. In this work we simulate the
improvement to the localisation capabilities of the HERMES-TP/SP when SpIRIT is
included in an orbital plane nearly perpendicular (inclination = 97.6$^\circ$)
to the HERMES orbits. For the fraction of GRBs detected by three of the HERMES
satellites plus SpIRIT, the combined constellation is capable of localising 60%
of long GRBs to within ~ 30 deg$^2$ on the sky, and 60% of short GRBs within ~
1850 deg$^2$. Based purely on statistical GRB localisation capabilities (i.e.,
excluding systematic uncertainties and sky coverage), these figures for long
GRBs are comparable to those reported by the Fermi GBM. Further improvements by
a factor of 2 (or 4) can be achieved by launching an additional 4 (or 6)
SpIRIT-like satellites into a Polar orbit, which would both increase the
fraction of sky covered by multiple satellite elements, and enable $\geq$ 60%
of long GRBs to be localised within a radius of ~ 1.5$^\circ$ on the sky.
