For the first time, remote bremsstrahlung X ray spatial, temporal, and spectral mappings from a satellite are presented for a strong energetic electron precipitation event following a sudden commencement. After the sudden commencement of July 13, 1982, and at the beginning of a magnetospheric substorm, X rays were observed over a period of more than 4 min from the P78-1 spacecraft at 600-km altitude. The X rays above 21 keV were emitted over a magnetic local time (MLT) interval spanning 6 hours. Five precipitating temporal spikes were observed with coherency over wide longitude intervals of 3 hours or more in MLT near midnight. The energy spectra over broad longitude intervals tended to be harder simultaneously at the times of greatest X ray intensity. The power input to the atmosphere from precipitating electrons that produced the X rays emitted within 2200--2230 MLT is estimated to have reached values of 5¿1016 ergs/s over an area of about 3¿104 km2, leading to an average energy deposition rate of about 160 ergs/cm2 s. The precipitation inputs at other magnetic local times displayed nearly simultaneous sharp maxima in time but with lower power inputs. ¿ American Geophysical Union 1987