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At 1817 75°W time on June 24, 1961, a two‐frequency pulsed radio sounder (ionosonde) was carried to an altitude of about 1060 km, east of Wallops Island, Virginia, by means of a fourstage, solid‐propellant rocket (NASA 8.15). Reflections from the topside of the ionosphere were obtained on one or both frequencies during 13 minutes of the flight. The objective of the experiment was to test the sounding system that is to be used in a satellite‐borne, fixed‐frequency topside sounder scheduled to be placed in orbit in 1962. The purpose of this short communication is to present the topside soundings obtained during the flight and to describe some preliminary results of the experiment.