The US’ National Defence Space Architecture will bring impressive levels of space-based connectivity down to the tactical edge.
The US Department of Defence’s Space Development Agency (SDA) is leading the National Defence Space Architecture (NDSA) initiative. In the words of the agency’s own literature, this will create “a resilient military sensing and data transport capability”. Low Earth Orbit (LEO) satellites communications will form the backbone of the NDSA. These are typically defined as having an orbit under 540 nautical miles/nm (1,000 kilometres) above Earth. The SDA’s literature adds that the NDSA will be delivered in several tranches, starting in 2022.
The NDSA includes several ‘layers’ each of which delivers a specific capability. These will not necessarily be space-based. For example, the support layer encompasses NDSA Earth-based assets and the satellite’s launch infrastructure.
The NDSA will have sensing capabilities to detect and track ballistic and hypersonic missiles. A ‘custody’ mission will provide weapons-quality intelligence, surveillance and reconnaissance data. The transport layer will use the LEO satellites to form a space-based mesh later. This backbone will carry data between the NDSA’s respective applications.
The transport layer will interact closely with the Battle Management Layer (BML). The BML will take incoming information like tracking data for ballistic missiles fusing this with other relevant information. For example, missile launcher’s coordinates could be moved across the transport layer so that the launcher can be engaged with kinetic or electronic weapons. The SDA’s literature says the BML will rely heavily on cloud computing to fulfil this mission.
Tranches
NDSA functions are being spirally implemented via a series of tranches, each of which will see new capabilities added to the NDSA repertoire. The SDA awarded a contract for 126 Tranche-1 transport layer satellites in February. Launch is scheduled for 2024. These satellites will host tactical datalinks and accommodate the NDSA’s Position, Navigation and Timing (PNT) application. This provides an alternative to Global Navigation Satellite Systems (GNSS) like the US GPS (Global Positioning System) constellation. PNT data will be transmitted down from the satellites to users on Earth.
Tranche-2 will expand Tranche-1’s capabilities to the global level with hundreds of additional satellites. It is scheduled for launch in 2026. Scheduled for 2028, Tranche-3 will improve the NDSA’s missile defence capabilities still further, improve targeting, add PNT capabilities and radio links. Tranche-4 is scheduled for 2030, although the literature does not disclose its capabilities. Over the longer term, the SDA plans to field new capabilities every two years as new satellites are added and old satellites replaced.
Transport Layer
The communications provided by the transport layer satellites will be “a completely new capability not currently available,” Frank Turner, the NDSA’s technical director told Armada. Initially, Link-16 Tactical Datalink (TDL) traffic will be carried across the 126 satellites constituting Tranche-1. Link-16 uses wavebands of 960 megahertz/MHz to 1.215MHz.
The advent of Link-16 on the Tranche-1 spacecraft will let this traffic be carried over intercontinental distances. At present, Ultra High Frequency (UHF) Link-16 transmissions are limited to a line-of-sight range. Carrying Link-16 across the NDSA network will yield tactical and operational benefits, particularly across large theatres of operations with widely dispersed assets.
Further TDLs could be introduced on future NDSA tranches. Dr. Turner stated that discussions are ongoing on future tranches carrying Link-22 TDL traffic. Link-22 uses frequencies of two megahertz to 30MHz and 225MHz to 400MHz. It is progressively replacing Link-11 as the standard naval TDL for North Atlantic Treaty Organisation members and allied nations. Other possibilities include Collins Aerospace’s Tactical Targeting Network Technology (TTNT). TTNT is an internet protocol-based waveform hosting up to 200 users on a single network. It is designed to securely carry voice, data and imagery traffic down to the tactical edge over a mobile ad hoc network.
Although providing enviable tactical connectivity, the NDSA’s transport layer will have operational and strategic benefits. “The NDSA transport layer has been designated as the backbone for Multi-Domain Operations (MDO) and the Joint All-Domain Command and Control (JADC2) system,” says Dr. Turner. In a nutshell, JADC2 connects all sensors used by all the US’ military services into a single network. MDO is the ability of all services to fight seamlessly across all domains of warfare. JADC2 is the connectivity that will make MDO a reality: “Any sensor can be connected to any shooter”, Dr. Turner adds, and the NDSA’s transport layer will make this happen.
He says users will not necessarily have to develop or acquire new satellite communications terminals to equip their platforms, weapons, sensors or bases to access the transport layer. “If you have access to Link-16, you’ll have access to the transport layer”. The transport layer will haul traffic across military Ka-band links (10.9GHz – 14GHz). Thus, users who already have Ka-band terminals can automatically access the transport layer. As the NDSA unfolds it is possible that other satellite communications bandwidths will be handled by future generations of satellite. Ka-band makes sense as it is not overly congested, and relatively robust against detection and jamming because of the narrowness of its beam. It also carries enviable quantities of data.
Dr. Turner expects that an initial operational capability will be declared for the Link-16 provision on the transport layer by September 2024. “Early 2025 is our best estimate of when the warfighter will be able to move data over NDSA-provided Link-16.”
by Dr. Thomas Withington
