Advanced Extremely High-Frequency (AEHF) Satellite System, United States of America

AEHF satellites

The Advanced Extremely High-Frequency (AEHF) system is a series of four military communication satellites planned to replace the currently in-orbit Milstar system. It will provide extremely high-frequency (EHF) range uplink / crosslink capabilities and super high-frequency (SHF) range communications.

AEHF is part of the Military Satellite Communications Systems Wing's protected satellite communications (SATCOM) group. It is operated by the Air Force Space Command of the US Air Force.

The main function of the AEHF spacecraft in geostationary orbits will be to provide secure, survivable and near-worldwide satellite communications. It will provide military communications and jointly serve armed forces of the US and international partners - including the Netherlands, UK and Canada. Satellites will be more jam-resistant, secure, survivable and protected, offering global communications for sea, ground and air force assets.

The AEHF programme was started in 1999 and the development began in 2001. The first satellite, AEHF-1, was scheduled to launch in 2007. However, it was delayed due to difficulties, such as key cryptographic requirements.

It was finally launched in August 2010 from the Atlas V launch vehicle. The second satellite, AEHF-2, was launched in May 2012. Two more AEHF satellites (fifth and sixth) have also been contracted.

AEHF will allow a wide spectrum of missions to be carried out, such as strategic nuclear and defence operations, special operations, theatre missile defence, space operations and intelligence.

Operational capabilities of the USAF's satellite system

AEHF satellites are designed based on the A2100 satellite bus and are powered by hall current thruster electric propulsion. The thrusters control orbital eccentricity of the satellite during its repositioning. The satellite has a mass of 6,168kg at launch.

Capabilities of AEHF have been improved over the Milstar satellite system, as well as the MILSATCOM architecture. The throughput of the AEHF will be ten times higher than that of the Milstar satellites. AEHF also has substantially increased coverage area, providing connectivity across naval, air and land mission warfare.

The AEHF system consists of satellites in space, user terminals and ground mission control and associated communication network systems. The four satellites will be linked to form a constellation. They will provide continuous coverage from 65º south to 65º north latitude for 24 hours a day.

The mission control segment consists of mobile and fixed control stations and is highly survivable. It handles the satellites in orbit, monitors satellite health and provides monitoring and planning of operations.

The terminal segment is a network of both fixed and ground mobile, airborne, ship and submarine and other terminals of all the international partners. Only the air force terminal and space and ground segments will be acquired by SATCOM. These three segments enable communications and transfer of data at specified rates ranging from 75bps to about 8Mbps.

Payloads of the Advanced Extremely High-Frequency satellites

The AEHF communication satellite's anti-jam payload includes onboard signal processing, radio frequency equipment, crossbanded EHF / SHF communication antennas, routing and control software and hardware integral to the A2100 space vehicle.

It consists of two uplink / downlink antennas, two SHF downlink phased arrays, two crosslinks, one uplink EHF phased array, uplink / downlink earth coverage horns and six uplink / downlink gimballed dish antennas.

The payload controls the SHF downlink and crosslink functions, EHF uplinks, beam forming and onboard nulling. It also controls signal processing, time and frequency for extremely high, medium and low data rates of operation.

The AEHF constellation is more efficient and capable than the five current orbiting Milstar satellites. In-orbit processing and reconfigurable networks allow interoperability and dynamic command and control requirements. The satellite's antenna beams are electronically steerable and mappings can be made from channel to beam to achieve the required transmission capacity. Satellites can be crosslinked for enabling communications across the globe from different ground gateways.

Advantages of the tactical communication system include small and mobile terminals, dynamic routing and low detection probability. It will provide tactical military communications, including maps and real time videos of the battlefield. The satellites will also offer other critical survivable, endurable and protected communications. The system is also expected to address cyber threats.

Launching the military communication satellites

United Launch Alliance (ULA) successfully launched the first AEHF spacecraft from Space Launch Complex 41 at the Cape Canaveral Air Force Station, in August 2010.

The satellite was launched using the Atlas V 531 carrier under the project name USA-214 (AEHF SV-1). The satellite was deployed into the geosynchronous transfer orbit. The first two launch attempts were, however, unsuccessful due to malfunctioning of liquid apogee engine motor.

The second AEHF was launched from the base aboard a ULA Atlas V Evolved Expendable Launch Vehicle (EELV) 531, in May 2012. An RD Amross RD-180 engine powered the Atlas Booster.

Centaur upper stage was powered by a Pratt & Whitney Rocketdyne RL10A engine. It was launched successfully at the second attempt after the first one failed because of an overtemp condition on the Centaur Interstage Adapter purge.

AEHF-3 is expected to be launched in September 2013. The fourth satellite is currently under construction. Procurement of long-lead components have also been started for the fourth and fifth satellites.

Contractors for the US's AEHF constellation programme

Lockheed Martin Space Systems is responsible for the space and ground segments of the four AEHF satellites, including mission controls and system integration. Northrop Grumman Aerospace Systems is the payload supplier.

The US Air Force Military Satellite Communications Systems Wing at the Space and Missile Systems Center, at Los Angeles Air Force Base in California, is the project leader.

Vanguard Space Technologies has been subcontracted to fabricate and test two spacecraft bus structures of the satellites.

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