Editing Strategic Defense Initiative (section)

===Strategic Defense System===
Faced with this report and accompanying negative press, SDIO changed direction. Beginning in late 1986, Abrahamson proposed that SDI would be based on the system he had previously dismissed, a version of High Frontier now named the "Strategic Defense System, Phase I Architecture". The name implied that the concept would be replaced by more advanced systems in future phases.

Strategic Defense System (SDS) was the low-earth orbit (LEO) [[Smart Rocks]] concept with an added layer of ground-based missiles sited in the US. These missiles were intended to attack warheads that the Smart Rocks missed. In order to track them below the [[radar horizon]], SDS added more LEO satellites that would feed tracking information to both the space-based "garages" as well as the ground-based missiles.<ref>{{Cite web |access-date=2024-07-05 |website=U.S. Department of Defense |language=en-US|author=Missile Defense Agency |authorlink=Missile Defense Agency |url=http://www.defenselink.mil/specials/missiledefense/history.html |title=History of the Missile Defense Organization}}</ref> Later [[Ground-Based Midcourse Defense|ground-based systems]] trace derived from this concept.

LLNL then introduced the [[Brilliant Pebbles]] concept. This was essentially the combination of the sensors on the garage satellites and the tracking stations. Advancements in sensors and [[microprocessors]] allowed this to be packaged in a small missile nose cone. Subsequent studies suggested that this approach would be cheaper, easier to launch and more resistant to counterattack, and in 1990 Brilliant Pebbles was selected as the baseline model for SDS Phase 1.