<P> Countermeasures of various types have long been a key part of warfighting strategy . However, with SDI they attained a special prominence due to the system cost, scenario of a massive sophisticated attack, strategic consequences of a less - than - perfect defense, outer spacebasing of many proposed weapons systems, and political debate . </P> <P> Whereas the current United States national missile defense system is designed around a relatively limited and unsophisticated attack, SDI planned for a massive attack by a sophisticated opponent . This raised significant issues about economic and technical costs associated with defending against anti-ballistic missile defense countermeasures used by the attacking side . </P> <P> For example, if it had been much cheaper to add attacking warheads than to add defenses, an attacker of similar economic power could have simply outproduced the defender . This requirement of being "cost effective at the margin" was first formulated by Paul Nitze in November 1985 . </P> <P> In addition, SDI envisioned many space - based systems in fixed orbits, ground - based sensors, command, control and communications facilities, etc . In theory, an advanced opponent could have targeted those, in turn requiring self - defense capability or increased numbers to compensate for attrition . </P>

Why did the soviet union object to the american strategic defense initiative (sdi)