Simulating the Double Asteroid Redirection Test (DART): Effects of impact parameters on momentum enhancement from a kinetic impactor
Abstract
The Double Asteroid Redirection Test (DART) is a NASA mission concept to test the kinetic impact deflection of an asteroid. DART would target the moon of the binary system Didymos ("Didymoon"), impacting at 6 km/s to change the moon's orbital period. DART represents the first direct test of the kinetic impactor theory for planetary defense. The momentum enhancement of Didymoon from the DART spacecraft is parameterized by _ and depends on the initial spacecraft momentum (pspacecraft) and the momentum of ejecta excavated during crater formation (pejecta): _=1+(pejecta/pspacecraft), with momenta tracked in the direction of intended deflection. An important part of mission development is determining the expected outcome of the impact, including crater formation and momentum enhancement from the impact. Impact modeling is one of the primary tools to be used to interpret the results of the kinetic impact deflection, to infer the physical properties of the target asteroid, and to advance our understanding of impact processes on asteroids. The DART team utilizes several state-of-the-art hydrocodes to simulate possible outcomes of the encounter.Target properties, including cohesion, porosity, and internal structure, may have significant effects on the momentum enhancement from a kinetic impact used to deflect an asteroid. Initial statistical analyses and modeling efforts suggest that the yield strength of the material, porosity, target cohesion and internal friction, and internal structure are the most important parameters to consider. Material porosity can come in the form of "microporosity" where there is void space among grains in the material, or "macroporosity" where the void space is along large-scale cracks or between large boulders if the asteroid is a "rubble pile". Both of these porosity types will affect the ejecta generated following impact, and thus the eventual momentum enhancement from the kinetic impact. Simulations of impacts into rubble piles show a wide range of momentum enhancements depending on the particulars of the internal structure, internal porosity, and where the impact occurs. Depending on the structure of the target (e.g., amount, size, and location of large boulders), impact outcomes can vary significantly. If the spacecraft were to impact onto a large, strong boulder, for instance, the cratering process and ejecta flow field will be significantly different than if the spacecraft were to impact into weaker granular matrix between boulders. In general, crater size and ejecta material (and thus, β_) are dominated by boulder material and whether the impactor strikes matrix or boulder material first. The internal damage propagation within the target is also sensitive to the presence of boulders, which may imply that disruption behavior is different.Further simulations are underway in order to fully explore this parameter space and map out the possible outcomes for the DART impact, and to estimate _ from the measured deflection of Didymoon. Portions of this work were prepared by LLNL under Contract DE-AC52-07NA27344. LLNL-ABS-746064.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E3263S