high and very sensitive to the timeline in which interceptors must be launched. As a result it is susceptible to countermeasures such as salvo launches that either delay and reduce its coverage or squander space-based intercepts.
• In principle, a constellation of satellites equipped with boost-phase interceptors could be configured so as always to be geographically in range for an intercept. The number of satellites required depends, in part, on the burn time and altitude of the threat missiles. Shorter powered flights of solid-fueled threat missiles require many more satellites for coverage. Shorter range missiles with their shorter burn times and lower burnout altitudes cannot be engaged by space-based boost-phase intercepts.
• The total life-cycle cost of placing and sustaining the constellation in orbit is at least an order of magnitude greater than that of any other alternative and impractical for that reason alone.
Space-basing for boost-phase intercept would, in theory, solve the problems of proximity that make surface- and air-based boost-phase interceptors generally impractical. In principle, a constellation of satellites equipped with boost-phase interceptors could be configured so as always to be geographically in range for an intercept. The number of satellites required would depend in part on what threats are to be defended against. Shorter powered flight times for the threat missiles would require more satellites for coverage.
A space-based system would have to overcome objections (and, arguably, legal obstacles) to “weapons in space.” More important, a space-based system would be vulnerable to the sort of primitive ASAT device that a country capable of deploying an ICBM would probably be able to develop.
The most powerful objection to a space-based system, however, is the total acquisition cost (both initial and replacement satellite costs plus launch costs) for the large number of satellites needed for continuous coverage of potential threat launch locations because of the relative motion of satellites in orbit to Earth below (see Appendix J in the classified annex). Some 700 satellites would be required for defense against liquid-fueled ICBMs and some IRBMs, with some residual capability against solid-fueled ICBMs. For confident defense against solid-fuel ICBMs, as many as 1,600 to 2,000 satellites would be needed. The total life-cycle cost of developing, building, launching into orbit, and maintaining in orbit, even an austere and limited-capability network of 650 satellites, for example, would be approximately $300 billion (in FY 2010 dollars). The cost for greater capability would be correspondingly greater. From an annual acquisition cost perspective, these relatively high costs over the time frame estimated to provide operational space-basing for boost-phase interceptors would probably prove unaffordable.