With concerns rising over nuclear-war-head capability in a number of countries, missile defense has become a core security strategy for the US and other nations. By using sensors that can receive infrared radiation, for example, demonstration satellites for the Space Tracking and Surveillance System (STSS) are able to detect and track ballistic missiles through all phases of flightfrom boost through the mid-course and terminal phases. They also can provide continuous target tracking and communications with missile-defense command and control systems. Recently, a communications crosslink for the STSS demonstration satellites was activated and successfully tested by Northrop Grumman Corp., prime contractor, and Raytheon Co., which provided the sensor payload. In a separate demonstration, the satellites also showed that they are ready to participate in Ballistic Missile Defense System (BMDS) tests.

In terms of the communications crosslink, the RF relay can keep a spacecraft that is out of view of a ground station connected to the system by means of a second satellite, which is in range of the ground station (see figure). As a result, the satellites' range of communications is expanded. Such enhanced communications will enable the destruction of targets as early as possible during their flight.

The missile-tracking capability that is being shown by the STSS demonstration program will further the design and concepts of operation for a future constellation. That operational constellation will be designed to enable earlier intercepts of threat missiles. In doing so, it should significantly improve missile- defense capabilities for the US, deployed forces, and allies.

Recently, the STSS demonstration satellites also showed that they are ready for Ballistic Missile Defense System (BMDS) tests. On-orbit calibration of the acquisitions and track sensors was completed for both spacecraft. The data generated during the BMDS tests is expected to validate value projections for spacebased sensors for missile tracking. It also will validate the models used to define an operational system. Among the missile-tracking capabilities that will be shown, for example, are boosting missile detection and tracking; mid-course object tracking and characterization; missile track handover between the two space vehicles; and interceptor cueing via downlink communications to the ground station.