Thrust from a multicycle pulse detonation engine operating at practical flight altitudes will vary with surrounding environment pressure. We have carried out the first experimental study using a detonation tube hung in a ballistic pendulum arrangement within a large pressure vessel to determine the effect that the environment has on the single-cycle impulse. Air pressure decreased below 100 kPa, whereas initial pressure of the stoichiometric ethyleneoxygen mixture inside the tube varied between

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... 100 and 30 kPa. The original impulse model (Wintenberger et al., ) was modified to predict the observed increase in impulse and blowdown time as the environmental pressure decreased below 1 atm. Comparisons between the impulse from detonation tubes and ideal steady-flow rockets indicate incomplete expansion of the detonation tube exhaust, resulting in a 37% difference in impulse at a pressure ratio (ratio of pressure behind the Taylor wave to environmental pressure) of 100.