Estimated shuttle loading emissions

As space shuttle tanks are loaded with N2O4, pressurization gas is displaced and at the same time N2O4 entering the tank evaporates and mixes with the pressurization gas remaining in the tank. Further addition of N2O4 to the tank requires venting of this mixture of N2O4/NO2 vapor and pressurization gas, which must be scrubbed prior to atmospheric release. A computer analysis was performed to estimate concentrations, flow rates, and total quantities vented during the planned fast fill/slow fill cycles of 125 gallon and 640 gallon space shuttle tanks. With helium as the pressurization gas, total vent quantities were estimated to be 4.5 and 24 pounds N2O4, respectively, for the two tank sizes.