Ions that absorb a great deal of the solar spectrum are ideal for plasma sails. Part of the quiet acceptance of fluorescent lighting has been the improvement in spectral color caused by innovative rare earth phosphors that coat the inside of the tubes. These phosphors absorb the mercury light and reradiate it efficiently at all wavelengths. If the same rare earth materials can be incorporated into a dust particle, they may provide a large improvement in solar spectrum opacity. These, and other advanced dust materials must be tested to quantify their various strengths and weaknesses.
For this purpose, an experimental facility based on an innovative technique referred to as electrodynamic balance has been under development for a few years at the Marshall Space Flight Center. The objectives are to carry out some basic experiments for understanding the micro-physics involved in the formation, charging, growth, and destruction of cosmic dust grains and to determine their extinction coefficients (absorption and scattering characteristics) in various astrophysical or planetary environments. The current work focuses on various charging process of dust particles, and some preliminary results been obtained and presented in various international meetings (e.g., Spann et al., 2000). Plans are under consideration for supplementing the existing apparatus with optical and cryogenic facilities for measuring the optical characteristics of levitated single dust grains of known composition under controlled pressure/temperature environments. The developing laboratory facility will be employed for measurements of extinction coefficients and scattering characteristics of dust grains considered to be suitable for development of the proposed propulsion systems employing magnetic balloon concepts. The experimentally determined data of optical characteristics of dust grains of desired composition, size, and shape will permit radiative transfer modeling of the solar radiation for accurate estimation of the total thrust on the magnetic balloon in varying space environments.
A pictorial view of the laboratory facility at MSFC shown in the second
panel of figure 2, employs an innovative experimental technique
that permits suspension of single test particles in an electrodynamic
cavity (e.g., Davis, 1985; Spann, 1985). The experimental apparatus is
divided into three functional groups: the particle generator, the
particle container, and the radiation source and detector. The particle
generator utilizes inductive charging to produce a charged particle. A
solution of the particle to be studied is placed in a tube, sealed at one
end with a metal plate containing an orifice and injected at the other
with a piston. The particle container is known as an electrodynamic
balance or a quadrupole trap (Davis, 1985). An alternating electric
field is applied between a ring electrode and two cap electrodes as shown
schematically below. For a charged particle in the trap volume, the
time-averaged electric field, coupled with the particle's inertia, causes
it to be confined to a null point of lowest potential. For experiments
requiring vacuum, the particle generator is removed and the trap is
evacuated to 
torr. Once the particle is trapped, it is
balanced at the null point of the trap by adjusting the potential between
the top and bottom electrode. Measurements of the parameters required
for balancing and suspension of the dust particle permits calculation of
the charge, mass and size of the particle.
Polarized tunable laser light sources detectors, combined with a tungsten lamp blackbody light source will be used to measure the optical characteristics of test dust particles in the visible and infrared spectral range. Comparison of the measured scattered light as a function of angle to that computed from Mie theory will be used to determine the index of refraction and particle size. The Mie scattering program of Wiscombe (1979) will be used to perform the data inversion in order to determine the optical properties and size of the particle. The computations of the intensity functions employing Mie theory, with measurements of the scattered intensities as a function of angle, permit calculations of the scattering phase matrix and the Stokes parameters providing information about the angular distribution of radiation scattered by the dust grain and the polarization characteristics.