Space Tracking and Surveillance System (STSS)

- , August 2020

Quick Facts

Mobility Deployed in Low Earth Orbit (LEO)
Role Demonstration for future space sensor capabilities; Track and discriminate missiles in all phases of flight and provide data for missile defense interceptors
Status Operational in LEO
Producer Northrop Grumman, Raytheon


The Space Tracking and Surveillance System-Demonstration (STSS-D) satellites were designed as demonstration satellites with a four-year in-orbit lifespan. The original four-year lifespan has been surpassed, with the satellites celebrating a decade in orbit in 2019. Additionally, despite original plans, there are currently no plans to replace or launch additional satellites within the STSS-D program. However, STSS-D serves as a demonstration capability for the birth-to-death tracking of cold objects in space, particularly ballistic missiles. The two satellites work as a part of the Missile Defense Agency’s risk-reduction mission and have been used continuously since their launch in 2009 in tandem with numerous missile defense projects and tests and their capabilities have also been used as the basis for developing future space sensors.

The aim of the STSS-D is to track ballistic missiles through all three phases of flight (boost, midcourse, and terminal); discriminate between warheads and decoys; transmit data to other systems that will be used to cue radars and provide intercept handovers; and provide data for missile defense interceptors to hit their target. During its time in orbit, STSS-D has operated in conjunction with tests that have included several other missile defense and offense programs, such as Terminal High Altitude Area Defense (THAAD), IBCM-III Minute Man, AEGIS, and the Ground-Based Interceptor (GBI).

STSS-D is able to track missiles against the cold background of space, particularly during the midcourse phase of flight, which is one of the biggest challenges of ballistic missile defense. STSS-D designers created the system to operate in conjunction with other U.S. missile defense and missile tracking systems, filling in gaps left by these systems. STSS-D is able to relay information to other systems, providing up-to-date information to guide missile defense interceptors and monitor possible missile threats. STSS-D has three main components: a wide-view acquisition sensor, a narrow-view tracking sensor, and a signal and data processor subsystem.[i]

The wide-view acquisition sensor detects an enemy ballistic missile just after launch when it is in the boost phase and its burners are hot. The acquisition sensor provides high-resolution, horizon-to-horizon detection capability and consists of a wide field-of-view scanning refractive telescope and a short-wave infrared focal plane array.

Once the missile has completed its post-boost phase and passes into its midcourse phase, the narrow-view tracking sensor picks up the threat and follows it as it travels through space. The tracking sensor includes a narrowly focused telescope that provides coverage above and below the horizon line. Even though a midcourse-phase ballistic missile does not have heat-producing rocket discharge, the narrow-view tracking sensor can detect the dim warhead.

As the wide- and narrow-view acquisition sensors and the narrow-view tracking sensor follow the enemy missile along its trajectory, the signal and data processor subsystem receives and filters the incoming data and transmits it to ground command centers such as the Command and Control, Battle Management and Communications (C2BMC) System fielded by numerous U.S. commands around the world.

MDA had originally planned a follow-on to STSS-D, the Precision Tracking Space System (PTSS), which would have used a simpler satellite that focused on cold-body missile tracking during the midcourse phase of flight, leaving the target acquisition role to SBIRS-High satellites. PTSS also planned to use a larger telescope than STSS, relying on subtle movements in space for tracking.[ii] Due to fiscal restraints and sequestration, however, the Pentagon terminated PTSS in its FY14 budget request.

Development– The MDA, NASA, and the Air Force launched the two satellites that make up the STSS-D constellation into low earth orbit from Cape Canaveral, FL in September 2009. The two satellites orbit at 1350 km, with a 58-degree inclination, and a 120 minute orbital period.[iii] The satellites are under the control of the Missile Defense Space Development Center (MDSDC) and completed an Early On-orbit Test series in November 2010, as well as additional interoperability tests with other systems such as Aegis and various parts of the Ballistic Missile Defense System. While the STSS-D satellites provide excellent theater coverage and tracking of missile launches, as many as thirty satellites would be needed to provide worldwide coverage.[iv]

Current Developments

Currently, MDA plans the keep the STSS-D satellites in operation for the foreseeable future. As a part of the maintenance and support of the satellites, Northrop Grumman Aerospace Systems was issued a contract in 2015 to provide on-orbit operations and sustainment for the STSS-D program. The program has also received regular financial support from the government through the Fiscal Year budgets and is set to receive an estimated $34.144 million dollars in the FY21 budget.

Additionally, in recent years, STSS has become a target of conversation as the DoD is working to convince Congress that the new HBTSS and Space Sensor Layer will not be a repeat of STSS or PTSS.

Strategic Implications

A major strategic implication of the STSS-D is its ability to demonstrate midcourse tracking from space. In March of 2011, STSS-D conducted a birth-to-death tracking of a ballistic missile launch, locking on to the heat signature of an ARAV-B short-range target missile that was launched from the Pacific Missile Range Facility in Kauai, Hawaii. Following the initial heat signature detection, the satellite then used its tracking sensor to lock on to the boosting missile, observing the target in all stages through space, atmosphere reentry, and landing in the ocean. Prior to this test, no birth-to-death tracking of ballistic missile had ever been conducted from space.[v]

Additionally, the demonstrative capabilities of STSS-D have served as the basis for the development of new missile defense systems, mainly the Hypersonic and Ballistic Tracking Space Sensor (HBTSS). Since the tests and use of STSS-D have been largely successful, the MDA is building off of its programming and capabilities, expanding the technology to be capable of tracking both ballistic and hypersonic missile threats.[vi] This allows for the MDA to have a quicker timetable for the development of HBTSS and to be more likely to achieve their expected launch date in FY23. However, this similarity between the programs has also been a cause for concern for leaders, some of whom who argue that HBTSS is going to be a repeat of STSS, PTSS, and SBIRS-low and will deal with the same technical, political, and budgetary issues. Despite this, movement on HBTSS continues forward, as the concern over increasing hypersonic and ballistic threats grows.


October 14, 2019: STSS satellites reach their tenth year in orbit, remaining in operation six years past they designed on-orbit life .[vii]

February 8, 2019: MDA awards an additional $17.4 million to Northrop Grumman for additional on-orbit operations and sustainment of STSS, bringing the total of their contract up to $1.9 billion.[viii]

March 31, 2017: Northrop Grumman completes on-orbit operations and sustainment period that began in April of 2016.

December 14, 2016: MDA announces the goal of bolstering STSS to extend the range of ground-interceptors as well as plans to extend the STSS lifespan past its planned retirement in 2017.[ix]

April 1, 2016: Northrop Grumman begins on-orbit operations and sustainment period at the Missile Defense Space Center in Colorado Springs, Colorado and Northrop Grumman Aerospace Systems in Redondo Beach, California.[x]

March 2016: Northrop Grumman awarded an $18.9 million modification to their STSS contract.

March 2015: MDA awards Northrop Grumman a $21.8 million modification for on-orbit operations and sustainment of STSS.[xi]

October 2013: The Precision Tracking Space System (PTSS) is canceled due to budget constraints.

February 13, 2013: The MDA and USS Lake Erie (CG 70) completed a successful intercept of a medium-range ballistic missile target over the Pacific Ocean by an SM-3 Block IA guided missile using STSS-D to detect and track the target, forwarding tracking data to the USS Lake Erie.[xii]

July 8, 2011: STSS-D conducts a successful test on a short-range air-launched target (SRALT).

March 16, 2011: STSS demonstrates first ever birth-to-death tracking of a ballistic launch missile.[xiii]

November 3, 2010: STSS completed a series of Early On-orbit Tests that tested 127 system functionalities and demonstrated the full calibration performance of both satellites, their crosslink systems, and ability and acquire and track sensor payloads.[xiv]

September 17, 2010: STSS successfully demonstrated autonomous handover to the tracking sensor.

June 28, 2010: STSS spotted and observed three missile-test launches and successfully relayed data about their trajectories to observers on Earth.[xv]

June 16, 2010: STSS-D satellites monitored an ICBM launch by the U.S. Air Force, detecting and tracking the Minuteman Missile as it flew 4,800 miles in 30 minutes before hitting its target near the Kwajalein Atoll in the western Marshall Islands.[xvi]

September 25, 2009: The MDA, NASA, and Air Force launched the two STSS-D satellites into low-earth orbit aboard a NASA Delta II launch vehicle from Cape Canaveral, FL.

August 13, 2007: Two significant milestone tests, the final STSS operational readiness demonstration and the testing of the ground system functions are completed[xvii]

2001: SBIRS-Low transferred to the Missile Defense Agency where it became the Space Tracking and Surveillance System.

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). Brilliant Eyes was then renamed as SBIRS-Low.

1980s:  STSS began as Space and Missile Tracking System (SMTS), also known as Brilliant Eyes under the Strategic Defense Initiative Office (SDIO).















[xiv] Ibid.


[xvi] Ibid.