close enough to catch it, making it much more expensive than the ICBM. The SDIO argued that such a response by the Soviets would be welcome; while the Soviets were deploying their fleet of new missiles to counter Pebbles, SDI would be on its way to deploying new systems based on directed energy weapons that could defeat those missiles. Critics noted that this meant the SDIO was arguing that Pebbles would lead to an offensive arms buildup, precisely the opposite of what they had previously claimed was the point of the entire SDI concept and contrary to the Nitze criterion. Another issue raised was that the existing Soviet A-135 anti-ballistic missile system could be fired at the Pebbles. By timing such an attack moments before an ICBM launch, the A-135 system's 100 missiles could temporarily "punch a hole" for their ICBMs to fly through. Because of the absentee ratio, 1,000 additional pebbles would have to be added to the fleet to counter this possibility, while costing the Soviets nothing at all. Finally, there was another overarching technical issue that affected all of the space-based weapons. Since the late 1970s, the Soviets had used ground-based lasers to "paint" United States satellites on a number of occasions, in some cases temporarily blinding them. The APS report noted that the amount of energy needed to do this was very low, far less than the amount of energy needed to destroy a missile. This meant that while it was still unknown whether one could ever build a useful directed-energy anti-ICBM weapon, it was already possible to build an anti-SDI weapon that would blind such a system's sensors. One commentator went so far as to note that protecting the optics was "impossible". Notes References Citations Bibliography Further reading Space Based Missile Interceptor Sizing Methodology, has a detailed examination of the weight and performance tradeoffs inherent to any kinetic-kill vehicle. Suggests that empty weight was around 20 kg and all-up weight including the life jacket was about 1850 kg. Based on this, they estimate the total cost of a fleet of 2600 pebbles would be $76 billion. Strategic Defense Initiative Missile defense