  According to the cold dark matter scenario, a large number of dark subhalos
should be located within the halo of each Milky-way sized galaxy. One promising
possibility for detecting such subhalos is to try to observe their
gravitational lensing effects on background sources. Dark matter subhalos in
the 10^6 - 10^10 M_solar mass range should cause strong gravitational lensing
on the (sub)milliarcsecond scales, which can be observed only using space VLBI.
We study the feasibility of a strong-lensing detection of dark subhalos by
deriving the image separations expected for density profiles favoured by
current simulations and comparing it to the angular resolution of both existing
and upcoming observational facilities. We show that the detection of subhalos
is likely much more difficult than suggested in previous studies, due to the
smaller image separations predicted for subhalo density profiles more realistic
than the singular isothermal sphere models often adopted.
