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Space Tracking and Surveillance System

The Space Tracking and Surveillance System (STSS) started service in 2009. Consisting of low-orbiting infrared satellites designed to detect and track ballistic missiles in all stages of flight, STSS data will allow U.S. interceptors to engage enemy missiles as early as possible in their trajectories and discriminate between warheads and their decoys.

Decades ago,  Pentagon realized that if it wanted to provide an effective defense against ballistic missile attack, it needed to create a quick and efficient method of detecting and tracking enemy launches. In other words, it needed to build an array of infrared satellites that would serve as the watchtower for the entire Ballistic Missile Defense System.

During the 1980s, a program to create a constellation of low-orbiting satellites known as “Brilliant Eyes” began under the auspices of the Strategic Defense Initiative Office (SDIO). In 1996, Brilliant Eyes was transferred to the U.S. Air Force, which had been given the responsibility of building a new Space-Based Infrared System (SBIRS) to replace the old defense Support Program (DSP). SBIRS, an integrated “system of systems,” was to include constellations of high- and low-orbiting satellites and a robust ground command center.

The initial plan for SBIRS had two concepts: (1) a Space-Based Infrared System-High (SBIRS-High) component – six large satellites deployed at 22,000 miles above the Earth; and (2) a Space-Based Infrared System-Low (SBIRS-Low) component (formerly Brilliant Eyes) – 20-30 smaller satellites in low-earth orbit roughly 621 to 930 miles above the Earth. In 2001, SBIRS-Low was transferred to the Missile Defense Agency (MDA) and in 2002 was renamed the Space Tracking and Surveillance System (STSS). Northrop Grumman is its prime contractor.

STSS has the responsibility of tracking enemy missiles against the cold background of space, one of the biggest challenges of ballistic missile defense. It is designed to observe its targets with great detail. To accomplish this mission, each satellite consists of three main components: a wide-view acquisition sensor, a narrow-view tracking sensor, and a signal and data processor subsystem.

In a combat scenario, the wide-view acquisition sensor will detect an enemy ballistic missile just after it has been launched, i.e. in its vulnerable boost phase when its rocket engines are burning hot. The acquisition sensor will provide high-resolution horizon-to-horizon detection capability. It will consist of a wide field-of-view scanning refractive telescope and a short-wave infrared focal plane array.

Once the enemy missile has completed its post-boost phase and passed into its midcourse phase, the narrow-view tracking sensor will pick up the threat and follow it through the cold vacuum of space. The tracking sensor will include a narrowly focused telescope that will provide coverage above and below the horizon line. Even though a midcourse-phase ballistic missile will not have heat-producing rocket discharge, the narrow-view tracking sensor will be cooled to cryogenic temperatures so that it will be able to detect the dim warhead.

As the wide- and narrow-view acquisition sensor and the narrow-view tracking sensor follow the enemy missile along its trajectory, the signal and data processor subsystem will receive and filter the enormous amount of incoming data. The processor will be capable of filtering 2.1 gigabits of data per second, which some have likened to reading an entire set of encyclopedias six times in one second. It will be able to simultaneously detect and track more than 100 objects in real time, and will differentiate missiles and warheads from decoys, debris, clutter, and noise. All the while, STSS will transmit this data to ground command centers to allow for quick and efficient interceptor launches.

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