SES Successfully Tests Stable Relay Link Between Medium and Low Earth Orbit

Luxembourg-based SES has achieved a significant milestone in satellite communications, successfully testing a stable relay communications link between one of its medium Earth orbit (MEO) satellites and a low Earth orbit (LEO) flight-representative terminal on the ground.

The test, conducted by SES Space & Defense, the U.S.-based subsidiary of SES, validated the performance of the Ka-band terminal, which is slated for demonstration in LEO early next year.

This effort is part of a $29 million Communications Services Project (CSP) contract awarded by NASA.

Planet, a San Francisco-based company operating an Earth imagery constellation, is a subcontractor on the project and provided the LEO terminals. While specific technical details were not disclosed, SES confirmed that Planet’s flight modem performed as expected throughout the tests.

This recent demonstration builds on similar tests conducted in November, where the companies established a relay link using a LEO flight-representative terminal and an SES satellite in geostationary orbit. That earlier test used lower-capacity C-band radiowaves for Telemetry, Tracking, and Command (TT&C) relay services.

SES is one of six companies awarded a CSP contract in 2022, with a total value of $279 million. The contracts aim to develop commercial alternatives to NASA's geosynchronous Tracking and Data Relay Satellites (TDRS), which are being retired. TDRS satellites have been crucial for relaying signals between spacecraft, including the International Space Station, and ground control stations, thus reducing data latency for LEO satellites that usually depend on a direct line-of-sight to communicate with ground stations.

NASA plans to have a commercial replacement for the TDRS system operational by 2030, as the current fleet is gradually decommissioned.

"With this end-to-end test and demonstration of capabilities, we were able to successfully showcase a complete data flow through our LEO Relay System (LRS) service...The data measurement results validated our multi-band commercial space relay service, set the stage for the flight demonstration as the next step, and for the future launch of the operational service offering." - David Fields, President and CEO of SES Space & Defense

In addition to SES, the other CSP contract awardees include SpaceX, Amazon’s Kuiper Government Solutions, Telesat U.S. Services, Viasat, and Inmarsat Government.

Viasat, which acquired Inmarsat last year, has recently announced partnerships with Loft Orbital and Rocket Lab to provide the LEO satellites needed for demonstrating relay terminals with its geostationary fleet in Ka and L-band.

Loft Orbital has scheduled a mission for fall 2025 to demonstrate high-capacity Ka-band relay links in orbit, while Rocket Lab is planning a demonstration for early 2026 to test space relay capabilities in Ka-band and TT&C services in L-band.

These developments mark significant steps toward ensuring continuous and efficient satellite communications as NASA transitions to commercial relay services, ensuring minimal disruption to vital space-based operations and scientific endeavors.