Active VLF Transmission Experiments Between the DSX and VPM Spacecraft

This study presents results from magnetic field line conjunctions between the medium-Earth orbiting Demonstration and Science Experiments (DSX) satellite low-Earth (LEO) very low frequencies (VLF) Propagation Mapper (VPM) satellite. DSX transmitted at VLF toward VPM, which was equipped with a single-axis dipole electric antenna, when two spacecraft passed near same line. VPM did not observe signals in any of 27 attempted conjunction experiments; goal this study, therefore, is to explain why were received. Explanations include (a) predicted power LEO transmissions too for observe; (b) VPM's trajectory missed “spot” highest intensity due focused ray paths reaching LEO; or (c) rays mirrored before VPM. Different combinations these explanations are found. We present ray-tracing analysis each event predict distribution wave normal angles vicinity altitudes. find that, low-frequency (below 4 kHz) transmissions, nearly all mirror LEO, resulting amplitudes LEO. For mid- high-frequency (∼8 28 kHz respectively), above noise threshold receiver (between 0.5 μV/m 1 μV/m). conclude that antenna efficiency plasmasphere model critical determining also most significant sources uncertainty could apparent discrepancy observations.