Last updated
Artist's impression of a Milstar Block I spacecraft
Manufacturer Lockheed Martin (prime)
Boeing (formerly Hughes)
Country of origin United States
Operator U.S. Air Force
ApplicationsMilitary communications
Bus Milstar Block I
Milstar Block II
Design life10 years
Launch mass4,500 kilograms (9,900 lb)
Regime Geosynchronous
StatusOut of production
Operational5[ citation needed ]
First launch USA-99, 1994-02-07
Last launch USA-169, 2003-04-08

Milstar (Military Strategic and Tactical Relay) [1] is a constellation of military communications satellites in geostationary orbit, which are operated by the United States Air Force, and provide secure and jam-resistant worldwide communications to meet the requirements of the Armed Forces of the United States.[ not verified in body ] Six spacecraft were launched between 1994 and 2003, of which five are currently operational;[ not verified in body ] the third launch failed, both damaging the satellite and leaving it in an unusable orbit.

Satellite constellation group of artificial satellites working in concert

A satellite constellation is a group of artificial satellites working in concert. Such a constellation can be considered to be a number of satellites with coordinated ground coverage, operating together under shared control, synchronized so that they overlap well in coverage, the period in which a satellite or other spacecraft is visible above the local horizon.

Military satellite artificial satellite used for military purpose

A military satellite is an artificial satellite used for a military purpose. The most common missions are intelligence gathering, navigation and military communications.

Geostationary orbit Circular orbit above the Earths equator and following the direction of the Earths rotation

A geostationary orbit, often referred to as a geosynchronous equatorial orbit (GEO), is a circular geosynchronous orbit 35,786 km (22,236 mi) above Earth's equator and following the direction of Earth's rotation. An object in such an orbit appears motionless, at a fixed position in the sky, to ground observers. Communications satellites and weather satellites are often placed in geostationary orbits, so that the satellite antennae that communicate with them do not have to rotate to track them, but can be pointed permanently at the position in the sky where the satellites are located. Using this characteristic, ocean-color monitoring satellites with visible and near-infrared light sensors can also be operated in geostationary orbit in order to monitor sensitive changes of ocean environments.



Milstar Block I spacecraft, or Milstar Developmental Flight Satellite (DFS)-1 and -2, were designed with a Low Data Rate (LDR) payload in the +X wing of the satellite that broadcast in the Super High Frequency (SHF) and Extremely High Frequency (EHF) ranges, and also a classified communication payload in the -X wing. The DFS-1 satellite was launched on 7 February 1994 aboard the first Titan IV(401)A rocket, but with the classified -X wing payload deactivated. It was followed by the DFS-2 spacecraft on 7 November 1995. DFS-2 was similar to DFS-1, but the classified payload was replaced by ballast in the form of a precision machined aluminum block to maintain the weight and balance characteristics of the satellite. Both Block I satellites (USA-99 and USA-115) are still operational as of August 2016, over 20 years since they were launched.

Titan IV family of rockets which were used by the U.S. Air Force

The Titan IV family of rockets were used by the U.S. Air Force. They were launched from Cape Canaveral Air Force Station, Florida, and Vandenberg Air Force Base, California. At the time of its introduction, the Titan IV was the "largest unmanned space booster used by the Air Force."

Ballast material that is used to provide stability to a vehicle or structure

Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship, submarine, or other floating structure that holds water is called a ballast tank. Water should move in and out from the ballast tank to balance the ship. In a vessel that travels on the water, the ballast will remain below the water level, to counteract the effects of weight above the water level. The ballast may be redistributed in the vessel or disposed of altogether to change its effects on the movement of the vessel.

The four later satellites were Block II spacecraft, which featured an additional medium data-rate payload. The first Block II satellite (DFS-3m, a hybrid mix of largely Block I support systems and LDR payload and a MDR (Medium Data Rate) Block II payload) was launched on 30 April 1999, using a Titan IV(401)B rocket. Due to a database error affecting the attitude control system of the Centaur upper stage of its carrier rocket, it was placed into a lower orbit than had been planned, and damaged by deployment at excessive rates. It could not be raised into its operational orbit due to fuel limitations. Its orbit was raised as much as possible to increase the expected lifetime and then it was permanently turned off after 10 days. It was the third consecutive, and last, failure of a Titan IV rocket. The remaining three satellites (DFS-4, -5, and -6) were launched on 27 February 2001, 15 January 2002, and 8 April 2003.

Centaur (rocket stage) family of rocket stages which can be used as a space tug

The Centaur is a family of rocket propelled upper stages currently produced by U.S. launch service provider United Launch Alliance. The 3.8 m diameter Common Centaur/Centaur III is the upper stage of the Atlas V launch vehicle, and the 5.4 m Centaur V is being developed as the upper stage of ULA's new Vulcan rocket.

The Milstar system consists of three segments; the space segment which consists of the six satellites, ground terminals and users, and stations to command and control the satellites. The Military Satellite Communications Systems Wing (MCSW) division of the United States Air Force Space Command Space and Missile Systems Center, located at Los Angeles AFB was responsible for development and acquisition of the Milstar space and mission control segments. The Electronic Systems Center at Hanscom AFB is responsible for the US Air Force portion of the terminal segment development and acquisition. The 4th Space Operations Squadron at Schriever AFB and the 148th Space Operations Squadron at Vandenberg AFB are responsible for providing real-time satellite control and communications payload management.

Military Satellite Communications Systems Wing

The Military Satellite Communications Systems Wing (MCSW) is a United States Air Force organization headquartered at Los Angeles Air Force Base, California. It is one of several wings and other units that make up the Air Force Space Command's Space and Missile Systems Center (SMC).

Space and Missile Systems Center Part of the US Air Force Space Command at Los Angeles Air Force Base in California

The Space and Missile Systems Center (SMC) is a part of Air Force Space Command of the United States Air Force, located at Los Angeles Air Force Base in El Segundo, Los Angeles County, California. SMC is the Air Force's product center for the development and acquisition of space and missile systems.

Electronic Systems Center former organisation within the Air Force Materiel Command, United States Department of Defense

Electronic Systems Center was a product center of Air Force Materiel Command (AFMC) headquartered at Hanscom Air Force Base, Massachusetts. Its mission was to develop and acquire command and control, communications, computer, and intelligence systems. ESC consisted of professional teams specializing in engineering, computer science, and business management. The teams supervised the design, development, testing, production, and deployment of command and control systems. Two of ESC's most well-known developments were the Airborne Warning and Control System (AWACS), developed in the 1970s, and the Joint Surveillance Target Attack Radar System (JointSTARS), developed in the 1980s.

In August 2010 control of the Milstar system was transferred to the Advanced Extremely High Frequency program, in preparation for the launch of the first AEHF satellite, USA-214. Advanced Extremely High Frequency satellites are intended to replace Milstar.[ citation needed ]

Advanced Extremely High Frequency

Advanced Extremely High Frequency (AEHF) is a series of communications satellites operated by the United States Air Force Space Command. They will be used to relay secure communications for the Armed Forces of the United States, the British Armed Forces, the Canadian Armed Forces and the Royal Netherlands Armed Forces. The system will consist of six satellites in geostationary orbits, four of which have been launched. AEHF is backward compatible with, and will replace, the older Milstar system and will operate at 44 GHz Uplink and 20 GHz Downlink. AEHF systems is a joint service communications system that will provide survivable, global, secure, protected, and jam-resistant communications for high-priority military ground, sea and air assets. It is the follow-on to the Milstar system. AEHF systems' uplinks and crosslinks will operate in the extremely high frequency (EHF) range and downlinks in the super high frequency (SHF) range.


USA-214, known before launch as Advanced Extremely High Frequency 1 or AEHF SV-1, is a military communications satellite operated by the United States Air Force. It is the first of four spacecraft to be launched as part of the Advanced Extremely High Frequency program, which will replace the earlier Milstar system.


Milstar satellites provide secure, jam resistant, worldwide communications to meet the requirements of the United States military. They were built by Lockheed Martin Missiles and Space Corporation, at a cost of US$800 million each. Each satellite has a design life of 10 years. Six were built, of which five reached their operational geostationary orbits, and remain in service. Launches were made using Titan IV rockets with Centaur upper stages, and all six occurred from Space Launch Complex 40 at the Cape Canaveral Air Force Station. The satellites are designed to provide communications which are hard to detect and intercept, and to be survivable in the event of nuclear warfare.

Lockheed Martin Corporation is an American global aerospace, defense, security and advanced technologies company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995, and Loral Federal Systems in 1996. It is headquartered in North Bethesda, Maryland, in the Washington, DC, area. Lockheed Martin employs approximately 100,000 people worldwide as of December 2017.

Cape Canaveral Air Force Station Space Launch Complex 40 launch pad at the north end of Cape Canaveral, Florida

Cape Canaveral Air Force Station Space Launch Complex 40 (SLC-40), previously Launch Complex 40 (LC-40) is a launch pad for rockets located at the north end of Cape Canaveral, Florida.

Nuclear warfare conflict or strategy in which nuclear weaponry is used to inflict damage on an opponent

Nuclear warfare is a military conflict or political strategy in which nuclear weaponry is used to inflict damage on the enemy. Nuclear weapons are weapons of mass destruction; in contrast to conventional warfare, nuclear warfare can produce destruction in a much shorter time and can have a long-lasting radiological warfare result. A major nuclear exchange would have long-term effects, primarily from the fallout released, and could also lead to a "nuclear winter" that could last for decades, centuries, or even millennia after the initial attack. Some analysts dismiss the nuclear winter hypothesis, and calculate that even with nuclear weapon stockpiles at Cold War highs, although there would be billions of casualties, billions more rural people would nevertheless survive. However, others have argued that secondary effects of a nuclear holocaust, such as nuclear famine and societal collapse, would cause almost every human on Earth to starve to death.

The spacecraft have a mass of 4,500 kilograms (9,900 lb), and are equipped with solar panels which generate eight kilowatts of electric power to power its transponders. Both Block I and Block II satellites provide low data-rate communications at bandwidths between 75 bit/s and 2,400 bit/s, whilst the Block II spacecraft can also provide medium data-rate communications between 4.8 kbit/s and 1.544 Mbit/s. The satellites' uplinks operate in the Q band, while their downlinks operate within the Ka band. The uplink corresponds to the extremely high frequency band while downlink corresponds to the super high frequency radio band.[ citation needed ]

Each Milstar satellite serves as a switchboard to direct traffic between terminals on the Earth. The satellites process the signals transmitted to them, and can link with other Milstar satellites through crosslinks, to reduce the requirement for ground-controlled switching. The spacecraft are used for encrypted voice, data, teletype, and facsimile communications, which are interoperable between the United States Army, Navy, Air Force, Marine Corps, and Coast Guard.[ citation needed ]


USA IDNameBlockLaunch date/time (UTC) COSPAR ID RocketRemarks
USA-99DFS-1Block I1994-02-07, 21:47:01 1994-009A Titan IV(401)A
USA-115DFS-2Block I1995-11-06, 05:15:01 1995-060A Titan IV(401)A
USA-143DFS-3MBlock I/II hybrid1999-04-30, 16:30:00 1999-023A Titan IV(401)B Launch failure
USA-157DFS-4Block II2001-02-27, 21:20 2001-009A Titan IV(401)B
USA-164DFS-5Block II2002-01-16, 00:30:00 2002-001A Titan IV(401)B
USA-169DFS-6Block II2003-04-08, 13:43:00 2003-012A Titan IV(401)B

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