the budget continued to grow, apparently without bound, first to $60 billion, to $75 billion, and then reaching $100 billion by April 1988. Brilliant Pebbles After Excalibur's failed tests in 1986, the program was about to be defunded. At that time, Livermore had no other major SDI programs. Teller and Wood were looking for a concept that would be feasible. The two had breakfast with Gregory Canavan, a Los Alamos physicist who worked on SDI related topics. Canavan noted that ongoing improvements meant microprocessors were on the verge of delivering supercomputer performance on a single chip. These chips were powerful enough that the processing capacity that formerly required the battle stations, or even computers on the ground, could now fit in the missiles themselves. Additionally, new sensors offered the optical resolution needed to track a missile at long range and still fit within a missile nose cone. Such a design offered an enormous advantage over the SDS; by flying freely, without a garage satellite, the interceptors could not be attacked en masse. If the Soviets wished to attack the system, they would have to launch an anti-satellite weapon for every one. Wood began exploring the idea using back-of-the-envelope calculations. Wood's "O-group" had been working for some time on new computing systems in their S-1 project that aimed to produce a "supercomputer on a wafer". He combined this with a new sensor system known as "Popeye". At the speeds the interceptors and ICBMs would be approaching each other, the mass of the projectile had six times the energy of an equal weight of TNT, meaning no warhead would be needed. Considering how small such a system could be scaled, he came up with a lower limit under . But if one considered armored ICBMs, a practical lower limit would be a burnout weight around , in order to have more than enough impact energy to destroy any conceivable fuselage. Considering the numbers required, it appeared a fleet would have on the order of 7,000 missiles in orbit, which would keep about 700 over the Soviet Union at any given time. The ratio of the total number of missiles in orbit to those available for action was known as the absentee ratio. If one wanted complete coverage against any potential attack, the numbers could reach as high as 100,000 missiles in total. Since the cost of each missile was expected to scale