“The first time we’ll be able to start working with our combatant commands … to start integrating space into their operations,” is how Acting Space Development Agency Director Gurpartap “GP” Sandhoo described the moment. On September 10, 2025, a SpaceX Falcon 9 launched 21 York Space Systems-designed satellites into low Earth orbit, marking the beginning of operations for the SDA’s Transport Layer Tranche 1 (T1TL) constellation a network intended to carry data at the pace of conflict.
These aren’t testbeds. They are designed for beyond-line-of-sight communications in contested and austere environments, providing encrypted connectivity directly to warfighters without intermediate ground relays. Every spacecraft has several Link 16 antennas the NATO-standard tactical data link to allow machine-to-machine communications between aircraft, ships, and ground units. They also have K-band radio frequency payloads for high-throughput video and bulk data, and a laser downlink terminal able to push large amounts of information directly to ground stations.
That laser capability, seen here for the first time on York’s satellites in pre-launch tests, is a major leap. SDA Director in an Outgoing Note Derek Tournear said, Laser communication … is a really good way to move a lot of data from space to ground. Now, it obviously is affected by weather … but we demonstrated that we can do that. That was the first time a very affordable, commoditized … commercial optical comm terminal was used to go from space to ground. That was the first time a highly inexpensive, commoditized … commercial optical comm terminal was employed to travel from space to ground. Optical downlinks, being vulnerable to atmospheric attenuation, can provide gigabit-class throughput with low probability of interception a desirable characteristic in electromagnetic warfare environments.
The T1TL network will ultimately consist of 126 satellites in six near-polar orbital planes, connected by optical intersatellite links (OISLs). These OISLs previously demonstrated in previous SDA tests with Tesat-Spacecom terminals provide the foundation for a robust mesh network, enabling data to jump from satellite to satellite until reaching the best point of downlink. This structure underpins the Pentagon’s Joint All Domain Command and Control (JADC2) concept, where sensors and shooters from services and domains exchange targeting information in near-real time.
OISLs’ engineering challenge is to keep the accurate pointing, acquisition, and tracking between rapidly moving satellites in low Earth orbit, which are typically several thousand kilometers apart and moving at relative velocities of more than 7 km/s. Thermal control, vibration isolation, and beam divergence control are important in keeping the tight optical link budget alive. Contractors like York, Lockheed Martin, and Northrop Grumman have used terminals to military interoperability standards, providing cross-vendor compatibility an intentional hedge against vendor lock-in.
The warfighter’s operation is significantly affected. In denied, disrupted, intermittent, and limited (DDIL) communications environments, widespread LEO constellations can offer hundreds of megabits per second with latency measured in tens of milliseconds, supporting cloud-based applications, ISR video streams, and targeting data to reach dispersed units. As Marine Col. Jason Quinter has noted, such bandwidth “really changes what’s possible on modern networks,” making hybrid cloud architectures operate at the tactical edge with no persistent connectivity.
The SDA’s spiral development strategy requires launching increasingly capable tranches every other year. Tranche 2, starting in 2026, will deploy over 200 satellites Alpha, Beta, and a smaller number of Gamma variants to provide regional to global coverage. The proposed Tranche 3 is now in doubt. The Department of the Air Force and Space Force are considering replacing it with a classified program called MILNET, possibly constructed on the SpaceX’s Starshield platform.
MILNET, which Space Force Col. Jeff Weisler described, would be a government-owned, contractor-operated network of as many as 480 Starshield satellites with optical crosslinks, managed by SpaceX under National Reconnaissance Office contract management. Starshield terminals would be used to access both the dedicated MILNET constellation as well as the commercial Starlink network. Supporters cite possible cost savings and quick deployment; critics, such as Sen. Chris Coons, caution that “no competition, no open architecture” threatens monopoly dependency on one vendor and the loss of the competitive environment that has fueled innovation in the SDA program.
In the meantime, the first 21 T1TL satellites will spend months being calibrated and tested before going into service, first in support of Indo-Pacific Command. With additional launches to come six to launch transport satellites and four to launch missile-tracking spacecraft within the next ten months the constellation will expand into a high-speed, multi-link, laser-empowered backbone for U.S. and allied forces, rewriting the playbook for how space assets are integrated into the fight.
