Theater SBI cost-effectiveness ratios

To address M missiles spaced at intervals longer than the constillation reconstitution time t, the defense needs at the absentee ratio N{sub a} of SBIs to fill the belt plus the M SBIs needed for the intercepts; the resulting cost effectiveness scales as M/(M + N{sub a}). N{sub a} is large and CER small for small ranges and numbers of missiles. For several-hundred missile threats, CERs are greater than unity for ranges of interest.