Spherical Probes for Measurements of Electric Fields on the INTERBALL-2 Satellite in the IESP-2M Instrument

The reliability and precision of satellite measurements of electric fields are significantly determined by the performance of probes used for these purposes. For measurements of the vector of the constant electric field and three components of the variable electric field in the frequency band from 0.1 Hz to 20 kHz on the INTERBALL-2 satellite, the method of a double probe and the scheme of three pairs of sensors are used. In manufacturing the sensitive units of the probes, an original Bulgarian technology for glass-carbon coating on their spherical surfaces was used. The results of measurements (by the Siesmann–Kelvin method) of variations of electron work function from the surface of the spherical probes with glass-carbon coating have shown mean statistical variations W < 0.006 eV. To minimize the errors in measuring electric fields, a construction of the probes as monoblocks with balancing and guarding electrodes was developed and used. The guarding electrodes are under a bias voltage in the limits from 0 to 12 V to decrease the influence of currents caused by photoelectrons emitted by different units of the satellite construction. The value of this bias was determined by choosing the working point of the voltage–current characteristic. The optimum value of the bias current for the auroral area was in the limits 70–100 nA. Output signals from the sensors of the IESP-2M instrument were used in measuring electric fields by the MEMO and NVK-ONCh instruments included in the wave complex.