Plasma Wave Signatures Associated with Dusty Space Debris

Space debris in Low Earth Orbit, roughly 200 km to 1000 km altitude, will continue to become an ever-increasing threat as more manmade objects inhabit space. Remediation techniques will rely on accurate detection using ground-based or space-based radio sounding and in situ measurements. Small objects of the order of cm are particularly difficult to detect but are still hazardous. Possibilities for detecting such small debris continue to be investigated and one possibility is the signature associated with a wide variety of plasma waves produced by the moving, supersonic, debris in the space plasma at this altitude. For example, past theoretical predictions include production of precursor ion acoustic solitons upstream from the debris and a typical wake field downstream. Magnetosonic waves in the magnetized LEO plasma produced by the debris have also been proposed. Some recent space-based measurements indicate electromagnetic Alfven waves and electrostatic lower hybrid waves may be observed in the vicinity of the debris. Another important phenomenon associated with the debris embedded in the LEO space plasma is charging due to fluxes of the charged particles onto the debris as well as photoemission in sunlight. It has been predicted that for debris larger than microns, there is no consequential impact on the actual orbit dynamics, however, there are possibilities for detection of the small, charged debris particles with various sensing techniques. The impact of the debris charging on the characteristics of the plasma waves must be considered. Fluctuations in the debris charge state could be important for the production and characterization of the waves produced by the debris. For example, in a dusty plasma of micron sized grains, it is known that fluctuations in the dust charge may excite or damp plasma waves. Also, as another example, plasma density and velocity inhomogeneities in the vicinity of the moving space debris have been proposed to produce plasma waves in the lower hybrid frequency band that have been observed by spacecraft. These inhomogeneities may be impacted by the debris charging as shown in the past in dust expansion across magnetized plasma. This work considers the impact of the debris charging on the production of plasma waves specifically in the lower hybrid frequency range. A hybrid Particle-In-Cell (PIC) and fluid plasma model is used to investigate production of lower hybrid waves due to motion of a debris cloud on the order of microns to centimeters through a magnetized plasma. The model uses the Orbit Limited Motion (OLM) model to describe time-varying charge on the debris cloud while the background fluid plasma density is self-consistently adjusted due to capture of plasma onto the debris cloud. The characterization of the plasma waves in the vicinity of the debris is considered for varying debris cloud and plasma parameters.