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
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.