We infer the polar mesospheric cloud (PMC) mass throughout the Arctic summer using results from two sets of satellite observations and a microphysical model. Solar backscatter ultraviolet (SBUV) PMC observations in July 1999 indicate a burst of activity persisting for ~8 days after a space shuttle launch and averaging 262 ¿ 52 t near 4.7 local time. This mass is consistent with the propellant mass available from the shuttle's main engines and accounts for 22% of the total SBUV PMC mass over the season between 65¿ and 75¿N. This is the first evidence that PMCs formed by space shuttle water exhaust can contribute significantly to both the number of observed PMCs and the total PMC mass in a season. In another approach, 11 years of observations by the Halogen Occultation Experiment (HALOE) indicate that on average 90 ¿ 12 t of water ice is present near local midnight between 65¿ and 75¿N. Using simultaneous HALOE water vapor observations, we find that a one-dimensional microphysical model reproduces the start and end of the PMC season but overpredicts the ice mass by about a factor of 1.8 when compared with the observations. This overprediction is within the time-dependent variability of ice formation and the uncertainties of temperature, water vapor, and vertical winds used to initialize the model.