IN Brief:
- Optical communications standards used by the Space Data Network Backbone and military missile-tracking constellations are not directly compatible.
- Space Systems Command has awarded five companies $12m each for connectivity demonstrations and initial Space Exchange Point development.
- Industry sources suggest that additional orbital relay spacecraft may be required, although the Space Force has not confirmed their number or cost.
The US Space Force is developing orbital communications exchange points to connect military satellite networks using incompatible optical-link standards, following the introduction of different laser communications technologies across major defence space programmes.
The problem concerns the Space Data Network Backbone, being developed by SpaceX, and optical terminals selected for other military satellite constellations. Equipment using the different standards cannot necessarily establish direct communications, creating additional integration requirements for the planned military data network.
Reporting published on 6 November identified the incompatibility between SpaceX's proprietary optical communications technology and terminals developed for Space Development Agency (SDA) spacecraft. A representative of the agency confirmed that its existing optical waveform is not directly compatible with SpaceX's system.
The Space Force has already established a Space Exchange Point (SEP) development programme intended to connect otherwise separate satellite networks. The service awarded five companies sets of contracts in August to demonstrate multi-vendor communications and begin developing the required orbital equipment.
Industry sources cited in the November reporting suggested that an eventual operational arrangement could require approximately 12 or 13 exchange-point satellites. However, the Space Force has not confirmed that quantity, the final equipment configuration, or an operational deployment timetable.
The wider Space Data Network is intended to transfer information between military and commercial spacecraft operating within different constellations. It is being developed as a shared communications architecture capable of connecting sensors, command systems, and other participating defence networks.
SpaceX received a $2.29bn contract in May to develop the network's backbone, with an operational prototype planned for 2027. The backbone is expected to use a large number of satellites providing high-capacity communications links within the wider architecture.
Optical inter-satellite communications use laser-based equipment to transmit information between spacecraft. Unlike conventional radio-frequency links, these systems operate at optical frequencies and can support substantial data transmission capacity when their equipment and operating conditions permit.
Maintaining a link requires accurate alignment between transmitting and receiving terminals. The equipment must acquire and track the intended connection while accounting for spacecraft movement, separation, and the physical characteristics of the optical system.
Compatibility also depends on the way information is encoded and transmitted. Optical terminals can use different waveforms, modulation arrangements, timing requirements, and communications protocols, preventing direct interoperability even where both systems employ laser technology.
SpaceX's backbone uses its proprietary Plaser optical communications terminals. The SDA has developed a separate optical terminal standard for its Transport Layer and Tracking Layer spacecraft, intended to provide common interfaces across equipment supplied by different manufacturers.
An SDA representative confirmed that terminals using the agency's existing standard cannot directly exchange data with the Plaser waveform. Sources also identified incompatibilities between SDA's equipment and optical terminals being developed for Space Systems Command's medium Earth orbit missile-warning satellites.
The latter incompatibility has not been publicly confirmed in equivalent technical detail by Space Systems Command. Its spokesperson declined to provide a detailed account of the relevant terminal standards, leaving the precise engineering differences unresolved.
Satellite altitude is one factor influencing optical communications requirements. Spacecraft in low Earth orbit can operate at different distances and relative velocities from systems in medium Earth orbit, with corresponding demands on optical terminal performance and link management.
These differences can influence the selection of equipment and operating modes. They do not automatically prevent interoperability, but compatible communications arrangements must be considered during system design if spacecraft operating in different orbital regimes are expected to exchange information directly.
The Space Exchange Point programme provides a possible route for connecting networks that already use different standards. The proposed spacecraft would act as orbital routing nodes, providing connections between participating systems and the Space Data Network Backbone.
Space Systems Command confirmed the development approach on 13 August. Amazon LEO for Government, Lockheed Martin, Northrop Grumman, Rocket Lab, and York Space Systems each received a complementary set of awards valued at $12m.
Each set comprises a $10m fixed-price contract covering multi-vendor communications demonstrations and a separate $2m agreement supporting the development and initial fielding of exchange-point capabilities.
The awards are intended to develop and demonstrate technical integration rather than purchase a complete operational constellation. Space Systems Command identified ground-to-space and space-to-space connectivity as principal demonstration requirements.
The exchange-point spacecraft are expected to incorporate optical communications equipment developed through the Enterprise Space Terminal (EST) programme. These terminals use a government-owned standard designed to support communications over different orbital distances.
Combining commercial spacecraft platforms with government-standard optical payloads is intended to provide a repeatable basis for integrating equipment from several suppliers. The final interfaces between the exchange points and SpaceX's backbone remain subject to development and demonstration.
Space Systems Command has not confirmed whether the prototype spacecraft will carry SpaceX Plaser terminals or explained the complete method by which incompatible optical signals will be translated between participating networks.
Such an integration arrangement would require more than physical accommodation of different communications terminals. Information received through one optical link must also be transferred through an appropriate processing and routing architecture, with compatible interfaces between the participating systems.
The spacecraft would need to support the electrical, thermal, structural, and operational requirements of its communications payloads. Additional terminals increase demands on spacecraft resources, while the final network architecture must account for the orbits and coverage required by the connected systems.
These requirements introduce engineering work involving payload integration, software, communications protocols, and the operation of the combined spacecraft system. The Space Force has not released the detailed configuration against which those technical functions will be qualified.
Another possible approach involves adopting an updated version of SDA's optical communications standard. Version 4.0.0 includes operating modes intended to address communications between spacecraft in different orbital regimes.
According to the SDA, the revised standard is under consideration for future satellite development but has not yet been contracted for deployment in an operational tranche. Its adoption could affect the interfaces required on later spacecraft, although no final decision has been announced.
The November reporting also raised questions about the cost of the additional orbital infrastructure. Industry and former government sources suggested that the integration requirement might involve approximately $1bn in further expenditure.
That estimate has not been confirmed by the Space Force and should not be treated as an approved budget, a contract value, or the established cost of a defined constellation. Space Systems Command declined to provide the final satellite quantity, programme cost, or deployment schedule.
The five prototype awards establish a confirmed initial investment of $60m across the selected contractors. The potential cost of a larger operational system remains a separate issue, dependent on its final architecture and acquisition requirements.
Space Systems Command expects the participating companies to undertake demonstrations during 2027. Those activities should provide evidence of whether the proposed interfaces and routing arrangements can connect the intended networks, while subsequent programme decisions will establish the scale and configuration of any operational deployment.
