Around fifty LORAN (LOng RAnge Navigation) transmitters in the northern hemisphere currently launch continuously pulsed 100 kHz radio waves into the Earth's atmosphere for marine navigation. It is discovered that the 100 kHz radio waves from the LORAN transmissions can be detected by the DEMETER satellite at an altitude of ∼660 km above the transmitters. These novel electric field measurements in space enable the determination of the nocturnal transionospheric attenuation by comparison with ground based electric field measurements. The electric field measurements on the satellite indicate that the nocturnal transionospheric attenuation of 100 kHz radio waves from LORAN transmissions is equivalent to a nocturnal subionospheric attenuation of the 100 kHz radio waves at a distance of ∼7–9 Mm. The radio waves exhibit an average subionospheric attenuation of ∼5 dB/Mm and it is concluded that the nocturnal transionospheric attenuation of 100 kHz radio waves is ∼35–45 dB. This result enables future space missions to quantify the intensity of lightning discharges associated with transient luminous events and terrestrial γ-ray flashes.