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. Later ground-based systems trace derived from this concept.
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. Later ground-based systems trace derived from this concept.