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 origins of the e ...
of
military
A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. It is typically authorized and maintained by a sovereign state, with its members identifiable by their distinct ...
communications satellites
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a Transponder (satellite communications), transponder; it creates a communication channel between a source transmitter and a Radi ...
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 service branch of the U.S. Armed Forces, one of the eight U.S. uniformed services, and the world's only independent space force. Along with its sister branch, the U.S. Air Force, the Space ...
, 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. The armed forces consists of six service branches: the Army, Marine Corps, Navy, Air Force, Space Force, and Coast Guard. The president of the United States is the ...
. Six spacecraft were launched between 1994 and 2003, of which five are currently operational; 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 to ...
(SHF) and
Extremely High Frequency
Extremely high frequency (EHF) is the International Telecommunication Union (ITU) designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). It lies between the super high frequency band and the ...
(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 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, ...
in the form of a precision machined
aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It 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 August 2016, over 20 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 ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse.
Centaurs are thought of in many Greek myths as being ...
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 (SM ...
(MCSW) division of the
Space and Missile Systems Center
Space Systems Command (SSC) is the United States Space Force's space development, acquisition, launch, and logistics field command. It is headquartered at Los Angeles Air Force Base, California and manages the United States' space launch ...
, 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 United States Space Force's Space Systems Command (SSC), which w ...
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 intelligenc ...
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 Field ...
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 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/Advanced Ext ...
at
Schriever AFB
Schriever Space Force Base, previously Schriever Air Force Base, Falcon Air Force Base, and Falcon Air Force Station, is a base of the United States Space Force located approximately east of Peterson Space Force Base near Colorado Springs in ...
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 AFB
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 th ...
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 (symbol: $; code: USD; also abbreviated US$ or U.S. Dollar, to distinguish it from other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American dollar, or colloquially buck) is the official ...
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 For ...
rockets with Centaur upper stages, and all six occurred from
Space Launch Complex 40
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 Space Force Station, Florida.
The launch pad was used by the United States Air Force for 55 Titan III a ...
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 statio ...
. 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 theoretical military conflict or prepared political strategy that deploys nuclear weaponry. Nuclear weapons are weapons of mass destruction; in contrast to conventional warfare, nuclear ...
.
The spacecraft have a mass of , and are equipped with
solar panel
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
s which generate eight
kilowatt
The watt (symbol: W) is the unit of 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 quantify the rate of energy transfer. The watt is named after James Wa ...
s of
electric power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...
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 (ITU) designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz (GHz). It lies between the super high frequency band and the ...
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 to ...
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 is be ...
*
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
The Wideband Global SATCOM system (WGS) is a high capacity United States Space Force satellite communications system planned for use in partnership by the United States Department of Defense (DoD), Canadian Department of National Defence (DND) ...
References
* King, Mak and Riccio, Michael J. ''Military Satellite Communications: Then and Now.'' Crosslinks Magazine. Aerospace Corp. Spring, 2010.
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