Mark Moretto
University of Colorado, Boulder
Comets represent valuable targets for scientific exploration. Their nuclei are believed to contain the most chemically pristine materials remaining since the formation of the Solar System; thus, comets represent a snapshot of the solar nebula at the time and location of their formation. Understanding comets is essential to understanding planetary formation and the distribution of volatiles and organics throughout the Solar System. Similarly to asteroids, comets can also impact the Earth, and though collisions are less common, they are usually higher energy, making it important to understand comets from a planetary defense perspective as well. The use of spacecraft to make in-situ observations of comets is necessary to study their nuclei and inner comae. Sample return from the pristine interior of a cometary nucleus is of great interest to NASA and the scientific community. Modeling the coma and its effect on a spacecraft orbiting the comet, the full 6 degree-of-freedom problem, in a robust and operationally efficient way is a major technological hurdle that, once addressed, will result in higher quality engineering and science. This problem is essential to proximity operations at a comet, especially sample collection.
I propose to use numerical and analytical techniques to characterize the dynamical environment of a spacecraft about an active comet and to apply this to science, navigation, operations, and mission planning, in order to enable the acquisition of high value science in close proximity to comets. This will involve building upon spherical harmonics and discrete jet models to describe the coma without using CFD. A generic method to describe the aerodynamic properties of the spacecraft (the coefficients of lift, drag, and moment) as a function of orientation and coma composition will also be developed. The dynamical environment will be characterized and dynamical phenomena will be correlated to coma properties. These models will be incorporated into navigation filters. Applications to operations and mission planning will be highlighted. A full touch and go sampling maneuver will also be simulated. Rosetta will serve as a test case to validate and calibrate both coma and spacecraft models. Coma properties will be backed out from Rosetta navigation data, enhancing the science data. Applications to Enceladus, Europa, and beyond will also be explored.