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Conventional ground-based observation methods, such as tracking radars, are unable to reliably detect and track subcentimeter orbital debris. This debris poses a risk to crewed and robotic spacecraft as it is capable of penetrating structures and damaging instruments. Tracking this debris reliably would allow for improved mitigation maneuvers to reduce mission risk. Based on recent publications, an alternate detection method could involve sensing plasma density solitary waves. These waves, henceforth “solitons,” are predicted to be produced by the interaction of the electrical charge on the lethal nontrackable debris with the local ionospheric plasma. This body of work seeks to test the feasibility of detecting the predicted soliton generated by defunct 1U CubeSats because they are already tracked using conventional methods and are predicted to produce solitons. Ground-based observers, such as incoherent scatter radars operated by the European Incoherent Scatter Scientific Association, may be able to detect the presence of solitons created by a CubeSat traveling through the ionosphere. This may be accomplished by observing the variation in electron density of the measurements near the time when the CubeSat passes through the radar beam.

Testing this hypothesis initially involves several 1U CubeSats that are propagated from their last time of observation until they overfly an incoherent scatter radar site during its operating cycle. In this observation window, the hypothesized soliton is modeled for each target of opportunity. The modeled solitons will travel with the CubeSats and are effectively pinned to them. These pinned solitons are compared with electron density measurements from the radar station. The variance in the measurements makes it unlikely to confirm an observation without a filter, but the apparently uncorrelated variance of the plasma density measurements is on the same order of magnitude as the one-dimensional soliton disturbances induced by the CubeSat. Based on this, a one-dimensional linear Kalman filter is implemented to look for positively correlated deviations of the electron density estimates when the debris is passing through the radar beam; three out of the five test targets are positively correlated and a fourth is nearly correlated.

Simulating the pinned solitons across a variation of times and altitudes indicates that there are better times of day and year to look for evidence of these solitons; the largest possible soliton for this data set is 140% the magnitude of the mean electron density. Further analysis of this best case scenario determines that it is unlikely any measurements could detect a deviation in electron density due to a soliton because of the size of the range gate and beam width relative to the signal size and strength. The range gate and beam width would need to be on the order of 1 meter as opposed to the 700 meter range gate in the test case. The sample rate would need to be less than 10 µs instead of 1 minute. Given this conclusion, the experimental evidence implies that there may be another factor causing the correlation algorithm to function as initially intended; perhaps the soliton is larger than predicted or the CubeSat itself is being detected in the measurement.