Artist's impression of an AEHF spacecraft |
|
| General Information | |
|---|---|
| Manufacturer | Lockheed Martin Northrop Grumman |
| Country of Origin | United States |
| Bus | A2100M |
| Applications | Military communications |
| Orbit regimes | Geosynchronous |
| Operator | US Air Force |
| Lifetime | 14 years |
| Production | |
| Status | In production Active |
| Built | 1 |
| On order | 3 |
| Launched | 1 |
| Operational | 0 |
| First launch | USA-214, 2010-08-14 |
| Typical spacecraft | |
| Average mass | 6,168 kg (13,600 lb) |
Advanced Extremely High Frequency (AEHF) is a series of communications satellites operated by the United States Air Force Air Force Space Command. The spacecraft will be used to relay secure communications for the Armed Forces of the United States, the British Armed Forces, the Canadian Forces and the military of the Netherlands. The system will consist of four spacecraft in geostationary orbits, of which one has been launched. AEHF will replace the older Milstar system and will operate at 44 GHz Uplink (EHF band) and 20 GHz Downlink (SHF band).[1]
AEHF spacecraft use a large number of narrow spot beams directed towards the Earth to relay communications to and from users. Crosslinks between the satellites will allow them to relay communications directly without the need to relay them to a ground station first. The satellites are designed to provide jam-resistant communications with a low probability of interception, and incorporate frequency-hopping. The spacecraft are equipped with adaptive antennas which can be used to cast antenna nulls towards sources of jamming.
AEHF incorporates the existing Milstar low data-rate and medium data-rate signals, providing 75–2400 bit/s and 4.8 kbit/sec–1.544 Mbit/s respectively. It also incorporates a new signal, allowing data rates of up to 8.192 Mbit/s.[2] When complete, the space segment of the AEHF system will consist of four satellites. which will provide coverage of the surface of the Earth between latitudes of 65 degrees north and 65 degrees south.[3]
The initial contract for the design and development of the AEHF satellites was awarded to Lockheed Martin Space Systems and Northrop Grumman Space Technology in November 2001, and covered the System Development and Demonstration phase of the program. The contract covered the construction and launch of three satellites, and the construction of a mission control segment. The contract was managed by the MILSATCOM Program Office of the United States Air Force Space and Missile Systems Center. Like the Milstar system, AEHF will be operated by the 4th Space Operations Squadron, located at Schriever Air Force Base.
The first satellite, USA-214, was successfully launched by an Atlas V 531 rocket on 14 August 2010, from Space Launch Complex 41 at the Cape Canaveral Air Force Station. This occurred four years behind scheduled; when the contract was awarded in 2000 the first launch was expected to occur in 2006. The National Security Agency has supposedly been blamed for being insufficiently responsive in providing cryptographic units. The program was restructured in October 2004, when the National Security Agency did not deliver key cryptographic equipment to the payload contractor in time to meet the launch schedule.[4]
Although the launch successfully placed the satellite into a supersynchronous-apogee transfer orbit with 50,000 km (31,060 mile) apogee, 275 kilometer (170 mile) perigee, 22.1° inclination,[5] the satellite vehicle's Liquid Apogee Engine failed to raise the orbit after 2 attempted burns.[6] To solve the problem, the perigee altitude was raised to 4700 km (2900 miles) with twelve firings of the smaller Reaction Engine Assembly thrusters, originally intended for orbital maintenance.[5] From this altitude, the solar arrays were deployed and the orbit was raised toward the operational orbit over the course of nine months using the 0.27 Newton Hall thrusters, a form of electric propulsion which is highly efficient, but low thrust. This took much longer than it would with the original apogee engine. This has caused delays, as the second and third satellite vehicle LAEs had to be analyzed. The investigation into the propulsion anomaly[7] has been completed (but not yet publicly released) and the remaining launch vehicles have been declared flight ready.[8] A Government Accounting Office 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.
Additionally, satellite access will also be delayed to no earlier than October of 2011, which will push system testing to a later date.