Fluctuations of Current onto Flat Probes of the ZOND–ZARYAD Instrument Mounted on the MIR Orbital Complex

Flat probes of the ZOND–ZARYAD instrument, which operated on the MIR orbital complex (OC), form a counterprobe (reference surface) configuration in which the alternating component of the net probe current is measured. There is no potential difference between the spacecraft (SC) body and the probes; that is, the probes are at the floating potential (FP). By measuring the alternating component of the probe current, one cannot estimate the FP value, but we can observe small-scale FP dynamics of a single probe in the OC near-surface region and estimate the fluctuations of currents flowing onto the SC. The alternating component of the current on the probes in the OC near-surface region varies in a wide range depending on ionospheric plasma parameters, the probe orientation with respect to the velocity vector, the magnetic field vector, and the direction to the Sun in the illuminated part of the orbit. In addition to the amplitude dynamics, the frequency dynamics of the alternating component of the current onto the probes is observed.