The computer programs for population defense would span thousands of computers all over the planet and in space. They would constitute the single largest software system ever written. There is absolutely no way we could ever be sure that the software would work correctly. To begin with, we cannot anticipate every possible scenario in a Soviet attack. Human commanders cope with unexpected situations by drawing on their experience, their common sense, and their knack for military tactics.
Computers have no such abilities.
They can only deal with situations they were programmed in advance to expect. Even if we could specify exactly what we want the computers to do, the task of translating that specification into flawless computer pro- grams would be beyond our capabilities for many, many years, possibly forever. Such testing is clearly not an option. To make nuclear weapons impotent and obsolete, SDI would have to be perfect. To shoot down Soviet satellites, to thin out a pre-emptive strike on U.S. missile fields, or to develop exotic new weapons for the conventional battlefield, SDI will only need to succeed on a much more modest level.