 Artist's impression of an AEHF satellite | |
| Manufacturer | Lockheed Martin Northrop Grumman |
|---|---|
| Country of origin | United States |
| Operator | United States Space Force |
| Applications | Military communications |
| Specifications | |
| Bus | A2100M |
| Launch mass | 6,168 kg (13,598 lb) |
| Regime | Geosynchronous orbit |
| Design life | 14 years (planned) |
| Production | |
| Status | Operational Active |
| On order | 0[1] |
| Built | 6[2] |
| Launched | 6 |
| Operational | 5 |
| Maiden launch | 14 August 2010 (USA-214) |
| Last launch | 26 March 2020 (USA-298) |
Advanced Extremely High Frequency (AEHF) is a constellation ofcommunications satellites operated by theUnited States Space Force. They are used to relay secure communications for theUnited States Armed Forces, theBritish Armed Forces, theCanadian Armed Forces, theNetherlands Armed Forces and theAustralian Defence Force.[3] The system consists of six satellites ingeostationary orbits. The final satellite was launched on 26 March 2020. AEHF is backward compatible with, and replaces, the olderMilstar system and will operate at 44GHz uplink (extremely high frequency (EHF) band) and 20 GHz downlink (super high frequency (SHF) band).[4] The AEHF system is a joint service communications system that provides survivable, global, secure, protected, and jam-resistant communications for high-priority military ground, sea and air assets.
AEHF satellites use many narrow spot beams directed towards theEarth to relay communications to and from users. Crosslinks between the satellites allow them to relay communications directly rather than via aground station. The satellites are designed to provide jam-resistant communications with a low probability of interception. They incorporatefrequency-hopping radio technology, as well asphased array antennas that can adapt theirradiation patterns in order to block out potential sources ofjamming.
AEHF incorporates the existing Milstar low data-rate and medium data-rate signals, providing 75–2400bit/s and 4.8 kbit/s–1.544 Mbit/s respectively. It also incorporates a new signal, allowing data rates of up to 8.192 Mbit/s.[5] When complete, the space segment of the AEHF system will consist of six satellites, which provides coverage of the surface of the Earth betweenlatitudes of 65° north and 65° south.[6][7] For northern polar regions, the Enhanced Polar System acts as an adjunct to AEHF to provide EHF coverage.[8]
The initial contract for the design and development of the AEHF satellites was awarded toLockheed Martin Space Systems andNorthrop Grumman Space Technology in November 2001, and covered the System Development and Demonstration phase of the program. The contract covered the construction and launch[9] of three satellites, and the construction of a mission control segment. The contract was managed by the MILSATCOM Program Office of theSpace and Missile Systems Center. Like the Milstar system, AEHF are operated by the4th Space Operations Squadron, located atSchriever Space Force Base and the148th Space Operations Squadron atVandenberg SFB.
It extends the "cross-links" among AEHF of earlier Milstar satellites, which makes it much less vulnerable to attacks on ground stations. As ageosynchronous satellite over theequator, it still needs to be supplemented with additional systems optimized for polar coverage in high latitudes.
In the April 2009 Defense Department budget request, Secretary of DefenseRobert Gates said he planned to cancel theTransformational Satellite Communications System, still in the design phase, in favor of additional AEHF capacity. Individual AEHF satellites, exclusive of launch expenses, cost US$850 million.
Prior to the AEHF, United States and allied military satellite communications systems fell into one of three categories:[10]
AEHF, however, converges the role of its widebandDefense Satellite Communications System (DSCS) and protectedMILSTAR predecessors, while increasing bandwidth over both. There will still need to be specialized satellite communications for extremely high data rate space sensors, such asgeospatial andsignals intelligence satellites, but their downlinked data will typically go to a specialized receiver and be processed into smaller amounts; the processed data will flow through AEHF.
AEHF satellites are sent into space using anAtlas V rocket under theEvolved Expendable Launch Vehicle (EELV) Program. The payload weight at launch is approximately 9,000 kg (20,000 lb); by the time it expends propellants to achieve proper orbit, its weight is approximately 6,168 kg (13,598 lb). The satellites will operate ingeosynchronous orbit (GEO) orbit; it takes over 100 days for the orbital adjustments to reach its stable geo-position after launch.
Uplinks and crosslinks are in theextremely high frequency (EHF) while thedownlinks use thesuper high frequency (SHF). The variety of frequencies used, as well as the desire to have tightly focused downlinks for security, require a range of antennas, seen in the picture:
Phased array technology is new in communications satellites, but increases reliability by removing the mechanical movement required for gimbaled, motor-driven antennas.
The low gain Earth coverage antennas send information anywhere in a third of the Earth covered by each satellite's footprint. Phased array antennas provide super high-gain earth coverages, enabling worldwide unscheduled access for all users, including small portable terminals and submarines. The six medium resolution coverage antennas (MRCA), are highly directional "spot" coverage; they can be time-shared to cover up to 24 targets. The two high-resolution coverage area antennas enable operations in the presence of in-beam jamming; the nulling antennas are part of theelectronic defense that helps discriminate true signals from electronic attack.[11]
Another change from existing satellites is using solid-state transmitters rather than thetraveling wave tubes used in most high-power military SHF/EHF applications. TWTs have a fixed power output; the newer devices allow varying the transmitted power, both for lowering the probability of intercept and for overall power efficiency.[citation needed]
The payload flight software contains approximately 500,000 lines of real-time, distributed, embedded code executing simultaneously on 25 on-board processors.[12]
AEHF provides individual digital data streams from rates of 75 bits/second to 8 Megabits/second.[5] These include and go beyond MILSTAR's low data rate (LDR) and medium data rate (MDR) as well as the actually fairly slow high data rate (HDR) for submarines. The faster links are designated extended data rates (XDR).
While there are a number of ground terminals, the airborne terminal has been part of theFamily of Advanced Beyond Line-of-Sight-Terminal (FAB-T) project. Other ground stations include theSingle-Channel Antijam Man-Portable Terminal (SCAMP),Secure Mobile Anti-jam Reliable Tactical Terminal (SMART-T), andSubmarine High Data Rate (Sub HDR) system.
With Boeing as the prime contractor andL-3 Communications andRockwell Collins as major subcontractors, the first FAB-T (Increment 1) was delivered, for use on theB-2 Spirit aircraft, in February 2009. It is planned for other aircraft including the B-52, RC-135, E-4, and E-6 aircraft. Other installations will go into fixed and transportable command posts. It successfully interoperated with legacy communications using a command post terminal and the Army Single Channel Anti-jam Man Portable Terminal,[13]
The first satellite, USA-214, was successfully launched by anAtlas V 531 launch vehicle on 14 August 2010, fromSpace Launch Complex 41 at theCape Canaveral Air Force Station (CCAFS). This occurred four years behind schedule; when the contract was awarded in 2000 the first launch was expected to have taken place in 2006.[14] The program was restructured in October 2004, when theNational Security Agency (NSA) did not deliver key cryptographic equipment to the payload contractor in time to meet the launch schedule.[15]
TheAtlas Vlaunch vehicle successfully placed the satellite into a supersynchronous-apogeetransfer orbit with aperigee of 275 km, anapogee of 50,000 km, aninclination of 22.1°.[16]
The satellite vehicle'sliquid apogee engine (LAE) provided by IHI failed to raise the orbit after two attempts.[17] To solve the problem, the perigee altitude was raised to 4700 km with twelve firings of the smallerAerojet Rocketdyne-provided Reaction Engine Assembly thrusters, originally intended forattitude control during the LAE engine burns.[16] From this altitude, thesolar panels were deployed and the orbit was raised toward the operational orbit over the course of nine months using the 0.27 NewtonHall thrusters, also provided by Aerojet Rocketdyne, a form ofelectric propulsion which is highly efficient, but low thrust. This took much longer than initially intended due to the lower starting altitude for the HCT maneuvers. This led to program delays, as the second and third satellite vehicle LAEs were analyzed.
AGovernment Accountability Office (GAO) report released in July 2011 stated that the blocked fuel line in the liquid apogee engine was most likely caused by a piece of cloth inadvertently left in the line during the manufacturing process.[18] While this is believed to have been the primary cause of the failure, aU.S. Department of Defense Selected Acquisition Report adds that fuel loading procedures and unmet thermal control requirements could also have contributed.[19] The remaining satellites were declared flight-ready a month prior to the release of the GAO report.[20]
Like the first AEHF satellite, the second (AEHF-2) was launched on an Atlas V flying in the 531 configuration. The launch from Space Launch Complex 41 at Cape Canaveral took place on 4 May 2012.[21] After three months of maneuvering, it reached its proper position and the testing procedures were started. Completion of checkout of AEHF-2 was announced on 14 November 2012 and control turned over to the 14th Air Force for operations for an expected 14-year service life through 2026.[22]
The third AEHF satellite was launched from Cape Canaveral on 18 September 2013 at 08:10 UTC.[23] The two-hour window to launch the satellite opened at 07:04 UTC[24] and the launch occurred as soon as weather-related clouds and high-altitude winds cleared sufficiently to meet the launch criteria.[23]
The fourth AEHF satellite was launched on 17 October 2018 from Cape Canaveral at 04:15 UTC using an Atlas V 551 rocket operated by theUnited Launch Alliance (ULA).[25]
The fifth AEHF satellite was launched on 8 August 2019 from Cape Canaveral at 10:13 UTC using an Atlas V 551 rocket.[26] Asecondary payload named TDO-1 accompanied the AEHF-5 satellite into orbit.[27]
The sixth AEHF satellite was launched on 26 March 2020 at 20:18 UTC by an Atlas V 551 fromCape Canaveral Space Force Station (CCSFS),SLC-41. It was the first launch of aU.S. Space Force mission since the establishment of the new military service.[28][29][30][31]
This article incorporates text from this source, which is in thepublic domain.Moreover, Capt Hill warned that US Air Force Space Command's Advanced Extremely High Frequency (AEHF) satcom constellation can be ineffective above the 65th Parallel North [...]
This article incorporates text from this source, which is in thepublic domain. This article incorporates text from this source, which is in thepublic domain.As ofthis edit, this article uses content from"Advanced Extremely High Frequency (satellite)", which is licensed in a way that permits reuse under theCreative Commons Attribution-ShareAlike 3.0 Unported License, but not under theGFDL. All relevant terms must be followed.
