STASS includes a user-friendly, three page, input and summary spreadsheet. The user may choose either the max principal or von Mises failure criteria for the design. The user may also input a minimum allowable skin thickness (as a manufacturing or fracture mechanics constraint). Primary products include internal volume calculations, skin thickness determination, and a mass summary. Using the minimum skin thickness calculated for each barrel section, STASS will then run a buckling analysis. Buckling analyses include bending moments, axial forces, shear forces, and ullage pressures. Using one of two stress methods, either the Space Shuttle External Tank Stress Report (1982) or Modified Beam Theory (Bruhn, 1973), STASS will check general instability, stringer crippling, local elastic buckling of the stringers, wide column buckling, and sheet buckling. The primary product of the buckling analysis is a margin of safety summary for each cylindrical barrel section. Microsoft Excel's add-in tool, Solver, can be used to optimize designs subject to multiple constraints.