Advanced Dusty Sail Concepts

Of course, changing the size and makeup (i.e., mass density) of the dust grains, or changing the dust grain density in the magnetic balloon, can have a major impact on the mass loading. One of the critical parameters in this calculation is the dust density. High dust densities ( $n_d > 10^5 m^{-3}$) are needed to ensure efficient light scattering to enhance the acceleration of the magnetic balloon. However, at these high densities, the mutual screening between the dust particles reduces the total charge that can be accumulated upon each grain. This competes against the fact that a relatively high grain charge is required to confine the dust within the balloon.

Figure 3: Left panel: Inverted gray-scale photograph of 3 micron diameter dust particles suspended beneath the anode of the Auburn University Dusty Plasma Experiment. Right Panel: Theoretical charge per dust grain as a function of dust grain density.

The scaling of the mass of the dust particles in the balloon and the effective charge on the grains is shown in figure 3. The figure indicates that even for the highest dust densities, the mass loading remains well below the target value of 1 gm/m$^2$. To address the issue of confinement, it may be possible to use non-spherical dust (e.g., cylindrical or conical) in order to promote strong coupling effects between the dust particles, thereby reducing the need toward larger dust grain charges. Additionally, the use of magnetic materials for the dust particle may sufficiently increase the magnetic field within the balloon to allow the dust particles to be confined, even with the lower charge. These are just some of the issues that will be addressed as part of this proposed project.

While the dust-filled magnetic balloon initially appears to satisfy the mass loading criterion of this AO, numerous basic physics and engineering issues must be addressed in order to demonstrate the feasibility of these ideas. Some of the most critical areas for investigation will be laboratory investigations of the confinement and density distribution of dust within the magnetic balloon and optimization of the choice of dust material (size, mass, coating, magnetic properties, etc.). Nonetheless, the initial calculations suggest that the addition of dust to the magnetic balloon can be a viable technique.