ABSTRACT The objective was to measure the neutron spectrum and total prompt gamms ray flux pro- duced by the detonation of a nuclear device of low yield at an altitude of about 90,000 feet. This information was to be obtainad by suitable detectors in the vicinity of the nuclear device and telemetered to the ground to be recorded and subsequently analyzed. The theory and instrumentation for measurement of neutron spectrum and total prompt~ gamma-ray flux from a nuclear device detonated at an altitude of 85,000 feet is described. Measurementof neutron time of flight with a Li'T scintillator-photodiode detector, with a similar Lil detector for gamma-ray correction of the Litt detector, was planned. The measurement was to have extended to plus 120 msec. A Cal scintillation detector, whose output was integrated for the first 10 usec after the zero time, and a KBr crystal, whose darkening was measured as a function of time for 120 msec after zero time, were to he used to detect gamma flux. The detector outputs were to have been electronically encoded and recorded on a magnetic-tape recorder programmed to record for 120 msec after zero time, reduce its speed to Ne of the recording speed, and continuously play back the data. The recorder output modulated a 70-ke voltage-controlled oscillator used in a standard frequencymodulated telemetering system. A ground station received and recorded the signal. The Bendix command system shared by this project and Projects 1.10 and 8.2 failed, and no data was obtained.