SpaceX has launched ten satellites for the Space Development Agency, a division of the U.S. Space Force. These satellites are the first of a batch of 28 communications and missile-tracking satellites referred to as “Tranche 0.”
The Space Development Agency refers to eight of these satellites as “Transport Layer” satellites. The name comes from the OSI Network Model, which describes a seven-layer process by which two or more devices communicate over a computer network. Most familiar networking protocols like HTTP, TCP/IP, and DNS can be placed on one of the layers of the OSI Networking Model.
The transport layer (Layer 4) describes the method by which data to be transmitted over a network is divided into packets and organized to send through the network. The Transport Layer satellites borrowed the name to describe their role in relaying information gathered by other satellites.
The other two satellites are infrared sensor satellites that can track missiles in flight. The Space Development Agency refers to them as “Tracking Layer” satellites. It plans to use the Tracking Layer satellites to monitor possibly hostile missile launches originating in China or Russia. Then the Tracking Layer satellites will relay that information to the Transport Layer to send to monitoring stations on the ground.
The Space Development Agency favors the redundancy that comes with development and launch of numerous low-cost satellites for critical services. With the upswing of small satellites and lower-cost launch options, it can develop satellite constellations that can still function even if a few satellites are disabled in a hostile nation’s attack. This plan is a departure from previous Department of Defense policies, which favored larger, more complex, and more expensive satellites.
“Satellite constellations must be proliferated, disaggregated and distributed” to help them withstand attack, Chief of Space Operations Gen. B. Chance Saltzman said during testimony before Congress on March 14. “The Space Development Agency’s proliferated warfighter space architecture provides a prime example of those efforts.”
SpaceX demonstrated the value of a large satellite constellation with robust cybersecurity by providing Ukraine with access to Starlink as it defends against the Russian invasion. It beefed up Starlink’s security to withstand efforts to interfere with the Starlink constellation, such as jamming satellites’ signal. SpaceX also barely blinked during an incident in which a group of Starlink satellites got wiped out by solar activity shortly after launch because it already had thousands of the satellites in orbit. It aimed to limit what SpaceX President Gwynn Shotwell describes as the “weaponized” use of Starlink on the battlefield but came up with an alternative called Starshield.
SpaceX has a second launch for the Space Development Agency’s Transport Layer satellites tentatively scheduled for June. The two launches are part of a $150 million contract awarded by the Space Development Agency in June 2020.
SpaceX reused a first stage booster that had been previously used to launch Starlink satellites. It landed the first stage booster, marking the 183rd time SpaceX successfully landed a first stage booster. The Space Development Agency likely saved some taxpayer dollars by agreeing to reuse a “previously flown” booster.