The P78–1 satellite was launched on February 24, 1979, into a 580-km sun-synchronous polar orbit. This U.S. Air Force Space Test Program mission is currently operational and continues to collect important earth and solar-related data.
Gamma ray spectrometers supplied by Lockheed (Palo Alto) measure sources with excellent spatial (≈100 km), spectral (3.5 keV FWHM at 511 keV), and temporal resolution (32 ms). Characteristics of energetic particle fluxes in the vicinity of the satellite are also monitored by Lockheed. Cosmic γ ray bursts have been observed with fine energy resolution. Mappings have been made of several bremsstrahlung X ray events resulting from electron precipitation, events which varied strongly with time (flux changes by 1–2 orders of magnitude in 5–10 s) and which extended coherently over distances of several hundred kilometers. Energy spectra of precipitating electrons have been observed with peaks as narrow as 20 keV, suggesting wave-particle interactions with waves of very narrow bandwidth (<1 kHz).