Electric field sensors - electric probes - are miniaturized copies of electric probes used for many spatial experiments in Former Soviet Union, starting from 1971. The theoretic study allowed to substantiate the possibilities of size reduction without sensitivity losses for ionospheric missions. The presented versions can provide the measurements of AC electric fields in frequency band from 0.1 Hz to 200 kHz in low Earth's orbits spatial experiments. Further development of electric probes able to provide the DC electric fields measurements too is now carried out.