Military Strategic And Tactical Relay
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Milstar (Military Strategic and Tactical Relay) is a
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...
of
military A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. Militaries are typically authorized and maintained by a sovereign state, with their members identifiable by a d ...
communications satellites A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. ...
in
geosynchronous orbit A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...
, which are operated by the
United States Space Force The United States Space Force (USSF) is the space force branch of the United States Department of Defense. It is one of the six United States Armed Forces, armed forces of the United States and one of the eight uniformed services of the Unite ...
, and provide secure and jam-resistant worldwide communications to meet the requirements of the
Armed Forces of the United States The United States Armed Forces are the military forces of the United States. U.S. federal law names six armed forces: the Army, Marine Corps, Navy, Air Force, Space Force, and the Coast Guard. Since 1949, all of the armed forces, except the ...
. Six spacecraft were launched between 1994 and 2003, of which only five were operational after launch; the third launch failed, both damaging the satellite and leaving it in an unusable orbit.


History

Milstar Block I spacecraft, or Milstar Developmental Flight Satellite (DFS)-1 and -2, were designed with a Low Data Rate (LDR) payload in the wing of the satellite that broadcast in the
Super High Frequency Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one ...
(SHF) and
Extremely High Frequency Extremely high frequency (EHF) is the International Telecommunication Union designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). It is in the microwave part of the radio spectrum, between t ...
(EHF) ranges, and also a classified communication payload in the wing. The DFS-1 satellite was launched on 7 February 1994 aboard the first Titan IV(401)A rocket, but with the classified 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 Ballast is dense material used as a weight 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 ...
in the form of a precision machined
aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
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 March 2025, over 25 years since they were launched. 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 A centaur ( ; ; ), occasionally hippocentaur, also called Ixionidae (), is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse that was said to live in the mountains of Thessaly. In one version o ...
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. 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 The Military Satellite Communications Directorate is a United States Space Force organization headquartered at Los Angeles Air Force Base, California. It is one of several wings and other units that make up the Space and Missile Systems Center ( ...
(MCSW) division of the
Space and Missile Systems Center Space Systems Command (SSC) is the United States Space Force's research and development, space development, Military acquisition, acquisition, space launch, launch, and Military logistics, logistics field command. It is headquartered at Los An ...
, located at
Los Angeles AFB Los Angeles Air Force Base (LAAFB) is a United States Space Force base located in El Segundo, California. Los Angeles Air Force Base houses and supports the headquarters of the Space Systems Command field command of the United States Space Fo ...
was responsible for development and acquisition of the Milstar space and mission control segments. The
Electronic Systems Center The 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 intellige ...
at
Hanscom AFB Hanscom Air Force Base (AFB) is a United States Air Force base located predominantly within Bedford, Massachusetts, with portions extending into the adjoining towns of Lincoln, Concord and Lexington. The facility is adjacent to Hanscom Fie ...
is responsible for the US Air Force portion of the terminal segment development and acquisition. The
4th Space Operations Squadron The United States Space Force's 4th Space Operations Squadron (4 SOPS) is a satellite operations unit located at Schriever Space Force Base, Colorado. 4 SOPS is part of Space Delta 8 and responsible for command and control of the Milstar/Adv ...
at
Schriever SFB Schriever may refer to: * Schriever, Louisiana, census-designated place named for John G. Schriever (see below) ** Schriever (Amtrak station) * Schriever Township, South Dakota * Schriever Air Force Base, a US military base near Colorado Springs, C ...
and the
148th Space Operations Squadron The United States Air Force's 148th Space Operations Squadron (148 SOPS) is a satellite control unit located at Vandenberg AFB, California. The 148th SOPS is tasked with back-up command and control of the MILSTAR satellite constellation. Missio ...
at
Vandenberg SFB Vandenberg Space Force Base , previously Vandenberg Air Force Base, is a United States Space Force Base in Santa Barbara County, California. Established in 1941, Vandenberg Space Force Base is a space launch base, launching spacecraft from the ...
are responsible for providing real-time satellite control and communications payload management. In August 2010 control of the Milstar system was transferred to the
Advanced Extremely High Frequency Advanced Extremely High Frequency (AEHF) is a constellation of communications satellites operated by the United States Space Force. They are used to relay secure communications for the United States Armed Forces, the British Armed Forces, the C ...
program, in preparation for the launch of the first AEHF satellite,
USA-214 USA-214, also known as Advanced Extremely High Frequency-1 or AEHF-1, is a military communications satellite operated by the United States Air Force. It is the first of six satellites to be launched as part of the Advanced Extremely High Freque ...
. Advanced Extremely High Frequency satellites are intended to replace Milstar.


Characteristics

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$ The United States dollar (Currency symbol, symbol: Dollar sign, $; ISO 4217, currency code: USD) is the official currency of the United States and International use of the U.S. dollar, several other countries. The Coinage Act of 1792 introdu ...
800 million each. Each satellite has a design life of 10 years. Six were built, of which five reached their operational
geosynchronous orbit A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...
s, and remain in service. Launches were made using
Titan IV Titan IV was a family of heavy-lift space launch vehicles developed by Martin Marietta and operated by the United States Air Force from 1989 to 2005. Launches were conducted from Cape Canaveral Air Force Station, Florida and Vandenberg Air Forc ...
rockets with Centaur upper stages, and all six occurred from Space Launch Complex 40 at the
Cape Canaveral Air Force Station Cape Canaveral Space Force Station (CCSFS) is an installation of the United States Space Force's Space Launch Delta 45, located on Cape Canaveral in Brevard County, Florida. Headquartered at the nearby Patrick Space Force Base, the sta ...
. The satellites are designed to provide communications which are hard to detect and intercept, and to be survivable in the event of
nuclear warfare Nuclear warfare, also known as atomic warfare, is a War, military conflict or prepared Policy, political strategy that deploys nuclear weaponry. Nuclear weapons are Weapon of mass destruction, weapons of mass destruction; in contrast to conven ...
. The spacecraft have a mass of , and are equipped with
solar panel A solar panel is a device that converts sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that produce excited electrons when exposed to light. These electrons flow through a circuit and produce direct ...
s which generate eight
kilowatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...
s of
electric power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...
to power its
transponders In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight trans ...
. 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 The Q band is a range of frequencies contained in the microwave region of the electromagnetic spectrum. Common usage places this range between 33 and 50 GHz, but may vary depending on the source using the term. The foregoing range corresponds ...
, while their downlinks operate within the K band. The uplink corresponds to the
extremely high frequency Extremely high frequency (EHF) is the International Telecommunication Union designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). It is in the microwave part of the radio spectrum, between t ...
band while downlink corresponds to the
super high frequency Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one ...
radio band.


Spacecraft


See also

*
Advanced Extremely High Frequency Advanced Extremely High Frequency (AEHF) is a constellation of communications satellites operated by the United States Space Force. They are used to relay secure communications for the United States Armed Forces, the British Armed Forces, the C ...
*
Defense Satellite Communications System The Defense Satellite Communications System (DSCS) is a United States Space Force satellite constellation that provides the United States with military communications to support globally distributed military users. Beginning in 2007, DSCS began ...
*
Transformational Satellite Communications System The Transformational Satellite Communications System (TSAT) program was a United States Department of Defense (DOD) program sponsored by the U.S. Air Force for a secure, high-capacity global communications network serving the Department of Defense, ...
* Wideband Global SATCOM system


References

* King, Mak and Riccio, Michael J. (Spring 2010). "Military Satellite Communications: Then and Now". ''Crosslinks Magazine''. Aerospace Corp.


External links


U.S. Air Force fact sheet on MILSTARMILSTAR 3 / Advanced Extremely High Frequency (AEHF)
{{USAF system codes Communications satellites Post–Cold War military equipment of the United States Lockheed Martin satellites and probes Military space program of the United States Equipment of the United States Space Force Military equipment introduced in the 1990s ja:アメリカ軍の衛星通信#MILSTAR