and reflected solar UV radiation and terrestrial IR radiation in order to obtain a better understanding of the driving forces of the Earth-atmosphere system. The primary instrumentation consisted of five bolometers in the form of hollow silver hemispheres that were thermally insulated from, but in close proximity to specially aluminized mirrors. The hemispheres thereby behaved very much like isolated spheres in space. Two of the hemispheres had black coatings and responded about equally to solar and terrestrial radiation. A third hemisphere, coated white, was more sensitive to terrestrial radiation than to solar radiation. A fourth, which had a gold metal surface, was more sensitive to solar radiation than to terrestrial radiation. The fifth hemisphere, protected from direct sunlight, was used to measure the reflected sunlight. A glass-coated bead thermistor was mounted on the top of each hemisphere to measure the temperature. A complete set of four temperature observations and one reference sample required 30 seconds. Thus, in each orbit, about 180 temperature measurements could be obtained. The experiment was a success, and usable data were obtained from launch until 28 February 1961. Significantly, it also carried Dr. Verner E. Suomi's flat-plate radiometer, improved with the help of Robert Parent, that took the first Earth radiation budget measurements from space and initiated the era of satellite studies of the climate. It made the first coarse maps of "the solar radiation reflected by the Earth and the infrared radiation emitted by the Earth". Using both satellite observations of the Earth's heat balance and atmospheric cooling rates measured by net flux radiosondes, Suomi established the important role played by clouds in absorbing radiated solar energy. These observations established that Earth's energy budget varies markedly due to the effect of clouds, the surface albedo, and other absorbing constituents. Using these instruments, Suomi and his team discovered that the Earth absorbed more of the Sun's energy than originally thought and demonstrated that it was possible to measure and quantify seasonal changes in the global heat budget. Explorer 7 was unable to detect solar X-rays due to its sensors being saturated by background radiation in the Van Allen radiation belt. Trapped Radiation and Solar Protons Two omnidirectional Geiger counters (Anton 302 and 112) were used to conduct a comprehensive spatial and temporal monitoring of total cosmic-ray intensity, geomagnetically trapped corpuscular radiation, and solar protons. The detector was sensitive to protons (E >20 MeV) and electrons (E