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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Brilliant Pebbles | 4/9 | https://en.wikipedia.org/wiki/Brilliant_Pebbles | reference | science, encyclopedia | 2026-05-05T13:24:19.440513+00:00 | kb-cron |
=== 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 1 gram (0.035 oz). But if one considered armored ICBMs, a practical lower limit would be a burnout weight around 1.5 to 2.5 kilograms (3.3–5.5 lb), 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 down into the $100,000 range, even the fully expanded system would cost $10 billion. Launch costs were not part of that estimate. If the empty weight was on the order of a few kilograms, then a single Space Shuttle could launch dozens, perhaps hundreds. They were so light that some consideration was given to launching them from the ground using a railgun. Such lightweight designs would have a limited "cone of action", carrying so little rocket propellant that they could only attack targets right in front of them. A larger interceptor with more propellant could attack more targets, so smaller numbers would be needed to provide coverage. In any event, launch costs would be greatly reduced compared to the baseline system that required hundreds of battle stations, each of which weighed 30 short tons (27 t) and could only be launched one at a time. Starting the next year, Wood had the former Excalibur team begin a more detailed study. By the fall of 1987, he had blueprints of the proposed design, a physical model to show, and computer simulations of the system in action. He also came up with a clever play on the Smart Rocks name, calling the newer, smaller, smarter concept Brilliant Pebbles. In another clever turn of phrase, one skeptical congressman would later refer to them as "loose marbles".
=== Pebbles becomes the Strategic Defense System ===
With Teller's help, Wood was able to brief Abrahamson on the concept in October 1987. Abrahamson was impressed enough to visit Livermore to view the mockups and watch the animated simulation they had created. This led to increased funding for further studies of the concept. In March 1988, Teller and Wood were able to directly brief President Reagan on the concept, taking the model pebble with them and theatrically hiding it under a black cloth when reporters were allowed to take pictures. Teller reiterated that the price for the system would be on the order of $10 billion. In May 1988, Abrahamson initiated the Space Based Element Study in order to refine the design of SDS's Space Based Interceptor (SBI). As part of this study, he had Livermore's work considered as one of the interceptor concepts. This study agreed with the basic concept that all the required sensors could be placed on the missile. While this was going on, the United States Air Force Space Division began a similar study on the baseline Space Based Interceptor. They also concluded that the sensors could be on the missiles, greatly simplifying the stations. For the next year, Wood and Teller ceaselessly advocated for Pebbles, to the point of it becoming something of a joke in Washington. During a briefing for reporters and congressional staff members, Charles Infosino, deputy director of the SDI architecture and analysis office, was quoted as saying "You may have seen Lowell Wood, who is responsible for this program, running around town with [a mockup] ... on a little cart." There were concerns about the changing estimates through this period; cost estimates for the pebbles were initially $100,000, but by the end of 1988 this had already risen to $500,000 to $1.5 million. Additionally, the sensor alone cost several million dollars and there was scepticism about whether this could be scaled down by a factor of 10 as Wood's estimates required.
=== Moving towards production ===