The US Space Development Agency is moving ahead with a large constellation of low Earth orbit satellites to support missile attack early warning and enhance SATCOM availability.
An artist’s rendering of the T2TL LEO satellite constellation. This graphic shows how the constellation can rapidly share information on ballistic missile launches over wide areas.
In late October, the United States’ Space Development Agency (SDA), itself part of the US Space Force (USSF), awarded contracts to build a constellation of 100 satellites. Known as the Tranche-2 Transport Layer (T2TL), the contract will provide “global communications access” in the words of an SDA press release.
Specifically, T2TL will provide encrypted communications to support beyond line-of-sight targeting, missile warning and missile tracking missions. T2TL forms a key part of the US Department of Defence’s (DOD’s) Proliferated Warfighter Space Architecture (PWSA). In a nutshell, the PWSA will develop, field and operate constellations of Low Earth Orbit (LEO) satellites. Established definitions state that LEO satellites orbit at altitudes below 2,000 kilometres/km (1,200 miles).
As a 2022 article in on the payloadspace.com website noted, the logic behind the PWSA is to take advantage of the cost and replaceability benefits of LEO satellites. Their lightweight and small size means that LEO spacecraft are less expensive to launch than their conventional counterparts. These cost reductions also mean they are less expensive to replace making them a relatively ‘disposable’ asset. Once launched, they will form part of the space connectivity for the DOD’s Joint All-Domain Command and Control (JADC2) system. More details on the composition and goals of JADC2 can be found here.
The T2TL satellites are being procured via two Other Transaction Authority prototype agreements worth a total of $1.3 billion. The two recipients are York Space Systems and Northrop Grumman. The former will deliver and operate 62 T2TL spacecraft with the latter delivering and operating 38.
Ka-band and Link-16
The SDA envisages an eventual fleet of between 300 and 500 satellites. The agency says that these LEO satellites will be placed at varying altitudes from 730km (394 miles) to 1,200km (648 miles) above Earth. The satellites will use optical inter-satellite crosslinks to move traffic between them. Traffic to and from Earth will be carried across Ka-band (26.5GHz to 40GHz uplink/18GHz to 20GHz downlink) channels.
Connectivity with Link-16 (960MHz to1.215GHz) Tactical Datalinks (TDLs) and the Integrated Broadcast System (IBS) will also be provided. Each satellite will carry a Link-16 payload. The IBS is an Ultra High Frequency (300 megahertz to three gigahertz) global US Army operational/tactical network. The key mission of the IBS is to facilitate delivery of the near real time intelligence to soldiers anywhere on Earth. Jonathan Withington, an SDA spokesperson, told Armada that the T2TL satellites will “provide the warfighter access to low-latency data connectivity via space-based extensions to existing tactical datalinks.” Employing Link-16 means US allies using this TDL can move data moved across the constellation, Mr. Withington continues.
Crucially the use of Link-16 and Ka-band makes the constellation compatible with communications systems already used by US forces. This removes the need to procure new SATCOM terminals so that personnel can access the T2TL. “To deliver capabilities into the hands of the warfighter, we must abide by our guiding principles, one of which says whatever we put up in our architecture must be compatible with receivers warfighters already use,” said Mr. Withington.
The T2TL constellation does not replace any existing US DOD constellations. Instead, it provides additional resilient satellite communications. The SDA press release continued that the T2TL satellites will be launched no later than September 2026. Mr. Withington said that he expects full deployment of the T2TL by 2027. US Space Force will operate the constellation from Redstone Arsenal, Alabama and Grand Forks airbase, North Dakota.
by Dr. Thomas Withington
