Understanding Projectile Geometry Effects on Momentum Enhancement during Hypervelocity Impacts

In 2022, the primary mission of the Double Asteroid Redirection Test (DART) mission will be achieved: the impact of the DART spacecraft with Dimorphos, the secondary body of Didymos. This impact will alter the orbital period of Dimorphos through a transfer of momentum, to test the efficacy of a kinetic impactor for planetary defense. The excess momentum that is transferred to a body when impacted at hypervelocity is characterized by the momentum enhancement factor (β). For hypervelocity impacts, it has been shown that β is greater than 1, and perhaps much larger, potentially on the order of 10.[1] The enhanced momentum transfer is due to crater ejecta leaving the impacted body, which acts like a thruster and pushes the target body. However, there is significant quantitative uncertainty in understanding β due to a lack of experimental data and uncertainty in the applicability of commonly used impact scaling laws. One major source of uncertainty stems from the geometry and scale of an impactor. Experimental hypervelocity studies are generally reported for simple projectile geometries - a sphere on a plate, for example. The DART impact will not be such a simple use case, and given previous work that has shown the sensitivity of β on impactor properties, it is necessary to investigate how realistic shapes and reduced geometries behave in a DART-like impact. Here, we use CTH to examine this in more detail by investigating the effects of the spacecraft's geometry on: β, crater shape, crater size and ejecta properties (mass and velocity distribution) by varying the projectile shape and density. Preliminary 2D results suggest that variations in simple projectile geometries do not produce a variance in β that is larger than the computation error resulting from the conditioning, stability and accuracy of CTH.

[1] C. R. Nysmith and B. P. Denardo, "Experimental Investigation of the Momentum Transfer Associated with Impact into Thin Aluminum Targets," National Aeronautics and Space Administration, 1969.