Lauchie Scott, Defense R&D Canada; Paul Bernhardt, University of Alaska Fairbanks; Andrew Howarth, University of Calgary
Keywords: plasma waves, ionosphere, conjunctions, space debris, non-traditional object sensing
Abstract:
This study describes in-situ experimentation to measure Very Low Frequency (VLF) plasma waves (3-30 kHz) at times when a space physics satellite equipped with a radio plasma wave receiver conjuncts with other space objects to learn if a secondary space objects rapid passage is detectable. Objects in Earths ionosphere develop a region of ion density rarefactions in the wake of their orbital motion. In 2022 in-situ experimentation attempted detection of these ion density rarefactions as broadband VLF plasma wave noise during a space-based radio plasma sensors rapid traversal of a secondary space object wake. This was undertaken to answer whether or not space objects are detectable by the plasma ion density disturbances that their orbital motion incurs in Earths ionosphere. The Canadian space physics satellite CASSIOPE activated its radio plasma physics package and recorded electric field data at times prior to, during and after a known close approach was forecast between CASSIOPE and a secondary object. CASSIOPE is designed to measure Earths aurora, particles and fields and has an eccentric 330 x 1408 km orbit which fortuitously samples a variety of plasma regimes in Earths ionosphere. Also, for the Space Domain Awareness community, this orbit regularly crosses the altitudes of highly populated orbital shells such as Starlink, Iridium, OneWeb and other space objects offering regular conjunction opportunities to attempt measurement of plasma oscillations during conjunctions. Prior to a conjunction, CASSIOPE collected electric field measurements from its crossed-dipole Radio Receiver Instrument (RRI) which detects plasma electric field oscillations spanning ~1-32 kHz. In 2022, 35 conjunctions were characterized. Four conjunctions exhibited VLF broadband noise energy spanning the ion cyclotron frequency (~200 Hz) to the Lower Hybrid Resonance frequency (~5-6 kHz) when the object passed through, or near, the secondary objects predicted wake. However, weak to strong correlation with the time of closest approach of the secondary object was found. Other conjunctions where secondary object passed behind CASSIOPE and the RRI did not pass through the secondary objects wake did not show wave power in excess of the ambient background emission – consistent with the prediction that plasma outside of a space objects ion-acoustic Mach cone would exhibit undisturbed plasma behavior. While density rarefactions in a space object wake appears to be weakly associated to conjunctions in the VLF range, these findings suggest that the spatial and time separation between detected wave energy and the secondary objects motion should be examined from a magnetohydrodynamic wave perspective where wave energy propagates relative to the geomagnetic field lines outside of the geometric constraints of a space object wake.
Date of Conference: September 19-22, 2023
Track: Space Debris