  NASA's Double Asteroid Redirection Test (DART) mission will impact its target
asteroid, Dimorphos, at an oblique angle that will not be known prior to the
impact. We computed iSALE-3D simulations of DART-like impacts on asteroid
surfaces at different impact angles and found that the the vertical momentum
transfer efficiency, $\beta$, is similar for different impact angles, however,
the imparted momentum is reduced as the impact angle decreases. It is expected
that the momentum imparted from a 45$^\circ$ impact is reduced by up to 50\%
compared to a vertical impact. The direction of the ejected momentum is not
normal to the surface, however it is observed to `straighten up' with crater
growth. iSALE-2D simulations of vertical impacts provide context for the
iSALE-3D simulation results and show that the ejection angle varies with both
target properties and with crater growth. While the ejection angle is
relatively insensitive to the target porosity, it varies by up to 30$^\circ$
with target coefficient of internal friction. The simulation results presented
in this paper can help constrain target properties from the DART crater ejecta
cone, which will be imaged by the LICIACube. The results presented here
represent the basis for an empirical scaling relationship for oblique impacts
and can be used as a framework to determine an analytical approximation of the
vertical component of the ejecta momentum, $\beta-1$, given known target
properties.
