On May 28, 1966, a vidicon spark-chamber detector was successfully flown for 6 hours at an altitude of 125 000 ft from the National Center for Atmospheric Research Balloon Flight Station at Palestine, Texas.Preliminary to the actual flight, extensive helicopter tests of the television telemetry system and thermal vacuum tests of the entire package were performed. Radio-frequency interference (RFI) from the spark discharges necessitated very careful shielding of the chamber from the electronic components.During the flight, while video data were being telemetered and recorded on kinescope film and magnetic tape, a constant visual check was kept on the television monitor to ensure that all systems were operating properly. In-flight solar calibration of an on-board magnetic compass yielded azimuth accuracies of [Formula: see text].Subsequently to the flight, a careful investigation was performed to determine the feasibility of incorporating a vidicon spark chamber into an Explorer-type satellite. Using slow-scan television, a design has been evolved that can satisfy the weight, size, power, and telemetry requirements of an Explorer-type system. With the proper vidicon system, sparks can be located to an accuracy of 0.1% and the resolution of two sparks to 0.5% to 1% of full sweep (1 to 2 mm in a 20-cm × 20-cm chamber). Only spark locations and intensity are stored in an on-board tape recorder and on command are telemetered to a ground station.