system and these should not be the basis for selecting some other system over SDS. The final study, carried out late in 1989, was an Air Force report making one last comparison between the SDS concept with simplified "gun rack" garages versus a Pebbles system, which concluded the former would cost $69 billion and the latter $55 billion. This system included only 4,600 pebbles, and some of the savings were due to the removal of the high-orbit Boost Surveillance and Tracking System (BSTS), a role the pebbles themselves would fill. Monahan had already given the DAB a "heads up" that major changes to the SDS concept were coming, and had been told to prepare a report for them for early 1990. The new system relied on Brilliant Pebbles as the baseline design. BSTS was not cancelled outright, but instead passed to the Air Force as a replacement for their existing Defense Support Program satellites. Other parts of the original design, including the land-based ERIS missile and its host of supporting radars and low-orbit satellites, remained. Early contract tenders were sent to six suppliers for production vehicles. Testing was to run in a two-phase program, some of it in parallel. To start, LLNL would supply prototype pebbles interceptors that would be tested both on the ground and in space after launch on sounding rockets. This series would conclude in February 1993, in time to allow the President to review the system and decide whether to proceed. Information from these tests would be fed back into the production designs. The first of these prototypes would begin testing in June 1990 and end in June 1993. Global Protection Against Limited Strikes A month later, another independent review by Henry F. Cooper strongly supported Brilliant Pebbles over the alternatives. Cooper's report went much further. Considering the major changes to the strategic outlook with the ongoing dissolution of the Soviet Union, Cooper stated that the massive attack that SDS was designed to defeat was no longer the only concern, or even the main one. Instead, it was United States forces in the field that bore the brunt of the missile threat, this time from short and medium range missiles. Although the SDS system should move ahead, he suggested that the system be modified to provide defenses against these new threats. Cooper noted that pebbles in their current form were designed to operate against a missile