Explorer 19 was the second in a series of 3.66-m inflatable spheres placed into orbit to determine atmospheric densities. Explorer 19 was launched while Explorer 9, the first satellite in the series, was still active, so that densities in two different portions of the atmosphere were sampled simultaneously. The satellite consisted of alternating layers of aluminum foil and plastic film. Uniformly distributed over the aluminum outer surface were 5.1-cm dots of white paint for thermal control. A 136.620-MHz tracking beacon, which was powered by four solar cells and was mounted on the spacecraft skin, used the electrically separated hemispheres of the balloon as an antenna. The spacecraft was successfully orbited, but its apogee was lower than planned. The beacon did not have sufficient power to be received by ground tracking stations, making it necessary to rely solely on the SAO Baker-Nunn camera network for tracking.