Advanced Extremely High Frequency
Artist's impression of an AEHF spacecraft
|Country of origin||United States|
|Operator||US Air Force|
|First launch||USA-214, 2010-08-14|
|Average mass||6,168 kg (13,598 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 Royal Netherlands Armed Forces. The system will consist of six spacecraft in geostationary orbits, of which three have been launched. AEHF will replace the older Milstar system and will operate at 44 GHz Uplink (EHF band) and 20 GHz Downlink (SHF band).
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 phased array antennas that can adapt their radiation patterns in order to block out potential 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. When complete, the space segment of the AEHF system will consist of six satellites, which will provide coverage of the surface of the Earth between latitudes of 65 degrees north and 65 degrees south.
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.
First AEHF Satellite (USA-214)
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 schedule; when the contract was awarded in 2000 the first launch was expected to occur in 2006. 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.
Failure of the kick motor, and recovery using the Hall-effect thrusters
The satellite vehicle's Liquid Apogee Engine (LAE) provided by IHI failed to raise the orbit after two attempts. To solve the problem, the perigee altitude was raised to 4700 km (2900 miles) with twelve firings of the smaller Aerojet-provided Reaction Engine Assembly thrusters, originally intended for attitude control during the LAE engine burns. 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, also provided by Aerojet, a form of electric 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. The investigation into the propulsion anomaly has been completed (but not publicly released as of June 2011[update])[dated info] and the remaining spacecraft were declared flight ready.
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.
Second AEHF Satellite (USA-235)
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. 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 Nov. 2012 and control turned over to the 14th Air Force for operations for an expected 14-year service life through 2026.
Third AEHF Satellite (USA-244)
The third AEHF satellite was launched from Cape Canaveral on 18 September 2013 at 4:10 a.m. EDT, The two-hour launch window to launch the satellite had opened at 3:04 a.m. EDT and the launch occurred as soon a weather-related clouds and high-altitude winds cleared sufficiently to meet the launch criteria.
- "Northrup Grumman AEHF". Retrieved 2011-06-15.
- "Northrop Grumman". Archived from the original on 2010-03-23. Retrieved 2009-11-11.
- "Lockheed Martin". Archived from the original on 11 October 2007. Retrieved 2007-09-12.
- GAO-07-406SP Defense Acquisitions: Assessments of Selected Weapon Programs, United States Government Accountability Office, March 30, 2007
- Justin Ray, SPACEFLIGHT NOW, "Air Force satellite's epic ascent should finish soon". October 9, 2011 (accessed Dec. 14 2011)
- "Main engine probably not to blame for AEHF 1 trouble". Archived from the original on 23 October 2010. Retrieved 2010-10-19.
- Justin Ray, SPACEFLIGHT NOW, "Investigators probing what went wrong with AEHF 1", Sept. 2, 2010 (accessed Dec. 14, 2011)
- "Air Force recoups costs to save stranded AEHF satellite". Retrieved 2011-06-15.
- "Spaceflightnow Mission Status Center". Retrieved 2012-05-02.
- "Spaceflightnow Mission Status Center". Retrieved 2012-11-28.
- Halvorsen, Todd (2013-09-18). "Atlas V roars to life with Air Force satellite onboard". Florida Today. Retrieved 2013-09-18.
- Atlas V to Launch AEHF-3, United Launch Alliance, accessed 2013-09-17.