US Space Force first mission, final Advanced Extremely.
United Launch Alliance’s Atlas V rocket will carry out its first mission for the United States Space Force Thursday, deploying the final Advanced Extremely High Frequency (AEHF) satellite to provide secure communications for the US military and its allies. Liftoff from the Cape Canaveral Air Force Station will take place during a two-hour window that opens at 14:57 Eastern Time (18:57 UTC).
The AEHF-6 satellite that will be carried into orbit by Thursday’s launch completes a constellation of satellites at the core of the US military communications. Originally a US Air Force program, deployment of Advanced Extremely High Frequency (AEHF) satellites began in August 2010.
United Launch Alliance (ULA) has launched all six satellites using Atlas V rockets. AEHF-6 will be the first satellite to be launched for the Space Force, which was formed in December when the former Air Force Space Command became a separate branch of the US armed forces.
Designed to augment and eventually replace the older Military Strategic and Tactical Relay (Milstar) satellite network, AEHF was conceived as a six-satellite constellation providing secure, survivable and jam-resistant protected communications to warfighters, military units and facilities around the globe. AEHF was later scaled back to three satellites before being expanded back to a six-satellite system with the cancellation of the successor Transformational Satellite (TSAT) program in 2010. Thursday’s launch will bring the constellation up to its full complement of satellites.
The AEHF satellites themselves were built by Lockheed Martin. They are based around the A2100M platform and each has a mass of about 6,168 kilograms (13,598 pounds). The spacecraft is designed to operate for at least fourteen years. Power comes from two deployable solar arrays, each consisting of five panels.
The propulsion systems aboard each satellite include a BT-4 liquid apogee motor built by Japan’s IHI Corporation, which is used for initial orbit-raising operations. Aerojet Rocketdyne XR-5 Hall Thrusters will be used for station-keeping one the satellite reaches geostationary orbit, while monopropellant thrusters – also developed by Aerojet Rocketdyne – will be used where additional attitude control is needed – on top of the reaction wheels that will provide day-to-day control.
AEHF’s communications payloads were developed by Northrop Grumman. To ensure backward compatibility with users of the legacy Milstar satellites, AEHF spacecraft support the same 2.4 kilobit-per-second low data rate (LDR) and 1.5 megabit-per-second medium data rate (MDR) signals as their predecessors. A new extreme data rate (XDR) signal provides speeds of up to 8.192 megabits per second.
The AEHF satellites carry multiple antennae to provide these services to users with varying requirements and use cases. A low-gain antenna provides coverage of the whole disc of the Earth visible to the satellite, six medium resolutions coverage antennae (MRCAs) produce 24 spot beams for focused coverage of specific areas, while two high-resolution coverage antennae (HRCAs) support jam-resistant tactical communications. Phased array antennae generate further spot beams that can be targeted around the world as required.
A pair of crosslink antennae allow direct satellite-to-satellite communications at rates of up to 60 megabits per second, allowing signals to be relayed between Milstar and AEHF spacecraft without passing through ground stations – enhancing the system’s survivability.