Where the laser relays sit in the geostationary belt

EDRS-C, the second satellite of Europe's laser data relay system, was launched to work at 31°E. ESA's EDRS page lists it at 31°E. ESA's space weather service, which runs a radiation monitor on the satellite, says it was moved on May 12, 2025 and has been at 142.5°E since June 15, 2025. The World Meteorological Organization's satellite database also lists 142.5°E, and public tracking data puts it at 142.52°E. We found this while listing the laser relays in the geostationary belt. There are five.

Clarke is a free public registry of who sits at each geostationary longitude. It combines public tracking data, the FCC's Approved Space Station List and the Union of Concerned Scientists (UCS) satellite database, whose data is current through May 1, 2023, and flags the places where they disagree.

The five relays

We counted a satellite if it is stationed in the geostationary (GEO) belt today, carries a laser terminal built to receive data from another spacecraft and pass it on, and the operator or a space agency has documented that terminal publicly.

Data as of October 22, 2026 (HKT). TLE epochs October 21, 2026. FCC Approved Space Station List dated September 27, 2026. The Clarke links return live values, so they will drift from this table over time.

Clarke takes each position from a two-line element set (TLE), the public orbit data for a tracked object. A TLE longitude is a snapshot at one moment, not an assigned slot. Satellites also move inside a small box. The ±0.1° figure often quoted comes from an ITU recommendation and Article 22 of the Radio Regulations, and it applies to satellites using fixed-satellite or broadcasting-satellite bands. Satellites that use neither, and experimental stations, have ±0.5°. Alphasat is a mobile-service satellite: ESA lists its main payloadas Inmarsat's L-band payload. We did not establish which tolerance its filing falls under. LCRD (112°W published, 111.86°W tracked) and Alphasat (25°E published, 24.86°E tracked) both differ by 0.14°. That is about the size of these boxes, published longitudes are often rounded, and a TLE gives the position at one moment, so we treat gaps of this size as noise. A gap of 111 degrees, as with EDRS-C, is not.

(a) EDRS-C has moved. ESA launched EDRS-C on August 6, 2019 to operate at 31°E. ESA's EDRS laser page is an undated explainer written in the present tense. A second ESA page, on its Connectivity and Secure Communications site, says "EDRS currently consists of two main nodes in geostationary orbit," with EDRS-C "operating at 31° East," so that page does present itself as current. Its metadata gives a last-modified date of January 7, 2026. Clarke's 31°E slot now lists it as a "ghost," meaning the old catalog puts it there but tracking finds it elsewhere. Its Ka-band payload is called HYLAS 3. In June 2026, SKY Perfect JSAT agreed to buy HYLAS 3 from Avanti and expects to operate it as JSAT-144D, covering East Asia, from early fiscal year 2027. EDRS's ground stations are in Belgium, the UK, Germany and Italy, according to ESA. Our own inference from geometry, not a published statement: a GEO satellite can see about 81 degrees of longitude either side of its position, and those stations are more than 120 degrees west of 142.5°E, so they should be below its horizon. We found no Airbus or ESA statement on what relay service, if any, EDRS-C now provides.

(b) STPSat-6 had a bad catalog row, which we fixed. The satellite is in the right place. The UCS catalog row for it has the launch vehicle, "Atlas 5," in the operator field and no usable longitude. Until October 22, 2026, Clarke showed no operator for the slot because of that row. We fixed the parsing that day, and the slot now shows US Space Force / DoD Space Test Program. NASA's LCRD is a hosted payload on STPSat-6, a Department of Defense Space Test Program satellite.

(c) None of the five has an FCC row. The FCC list covers space stations the FCC licenses, plus non-US satellites granted access to the US market. So most non-US satellites, including Eutelsat 9B, Inmarsat 4A-F4, EDRS-C and JDRS-1, do not appear. US federal satellites such as STPSat-6 get spectrum through the National Telecommunications and Information Administration (NTIA) instead of an FCC license. A hosted payload, such as EDRS-A on Eutelsat 9B, does not get a row of its own either.

What we left out. China's Shijian-20, now at 40.16°E, tested a 10 Gbps laser link to the ground in 2020, but that was a direct downlink, and we found no public record of a Chinese GEO satellite relaying another spacecraft's data by laser. China's Tianlian relay satellites are described as radio relays. ESA's ARTEMIS relay, which carried the SILEX laser terminal, reached end of life in November 2017. GEOLITE, a 2001 US satellite on the MIT Lincoln Laboratory timeline, has no public documentation of a relay role.

How these relays came about

A satellite in low Earth orbit (LEO) circles the planet in about 100 minutes and can only send data down when it passes over a ground station. ESA says this usually leaves about 10 minutes out of every 100. A relay in GEO stays over one longitude, so it can catch data from a passing LEO satellite and forward it to the ground straight away.

The MIT Lincoln Laboratory timeline lists ESA's SILEX experiment in 2001 and Japan's OICETS in 2005. Both linked LEO satellites to ARTEMIS by laser. In November 2014, ESA's Sentinel-1A radar satellite linked by laser to Alphasat, whose test terminal was built by Tesat. EDRS-A, a payload on Eutelsat 9B, launched on January 29, 2016, and EDRS-C followed in 2019. ESA lists the laser link at up to 1,800 Mbit/s, with a Ka-band radio link from the relay to the ground. Airbus, which owns and operates EDRS, said the service had passed 80,000 laser connections in 2024, and in December 2025 posted on LinkedIn that it had passed 100,000. We found the 100,000 figure only in that LinkedIn post.

NASA's LCRD launched on December 7, 2021 and began experiments in June 2022. Its first user in orbit, the ILLUMA-T terminal on the International Space Station, made its first link on December 5, 2023, sent data at 1.2 Gbps, and was decommissioned after testing ended on June 29, 2024. LCRD finished its two-year program that month and has run in an extended experiment phase since.

In January 2025, JAXA and NEC reported the first transfer of observation data from the ALOS-4 radar satellite to the ground through JDRS-1, at 1.8 Gbps.

Why lasers, and what limits them

NASA says laser links can carry 10 to 100 times more data than radio. JAXA puts the usable bandwidth near 1.5 micrometers at about 5 THz, and says the LUCAS beam spreads to only about 500 m over 40,000 km. Clouds block that light, so NASA chose high, mostly clear sites for LCRD's two optical ground stations, in California and Hawaii, and calls the ability to switch between stations "essential to reliable service."

Laser links also sit outside most spectrum rules. The International Telecommunication Union's radio rules cover frequencies up to 3,000 GHz, and an ITU note says interference between optical links between satellites is very unlikely. The MIT Lincoln Laboratory deck lists optical as "unregulated", with care needed around aircraft and sensor satellites. The host satellites still use radio. LCRD is normally commanded over STPSat-6's radio link, and EDRS sends data to the ground in Ka-band, so each host still needs its normal radio filings.

Deep space is a different setup

NASA's Deep Space Optical Communications experiment on the Psyche mission sent data straight to telescopes at Palomar and Table Mountain, with no GEO relay involved. It streamed video from more than 30 million km in December 2023 and downlinked data from about 494 million km on December 3, 2024. A GEO relay for deep-space links exists only as a 2014 NASA study concept. We found no such hardware in orbit.

Planned relays

Space Compass, a joint venture of NTT and SKY Perfect JSAT, signed with Swissto12 in March 2026 for what it calls the first commercial GEO optical data relay satellite, with no slot published. The U.S. Space Force is funding standard optical terminals and router satellites for its Space Data Network, but the contracted backbone and the Space Development Agency's Transport Layer are in LEO, and no GEO position has been announced.

For now, the list is short: five satellites, and one of them, EDRS-C, has moved more than 110 degrees east while two ESA pages still list the old slot. Published positions for these relays go out of date, so check the tracking data before relying on any of them.

Sources

1. ESA's EDRS page
2. ESA's space weather service
3. World Meteorological Organization's satellite database
4. 142.52°E
5. Clarke
6. current through May 1, 2023
7. Experiment, in extended phase since June 2024
8. 112°W (NASA paper)
9. 111.86°W
10. Operational service
11. 8.95°E
12. Demonstration, still in use in 2025
13. 25°E
14. 24.86°E
15. Operational
16. 90.75°E (JAXA 2017: same slot as its predecessor DRTS)
17. 90.7°E (third-party database)
18. 90.75°E
19. ITU recommendation
20. Article 22 of the Radio Regulations
21. launched EDRS-C on August 6, 2019
22. Connectivity and Secure Communications site
23. 31°E slot
24. SKY Perfect JSAT agreed to buy HYLAS 3
25. according to ESA
26. hosted payload on STPSat-6
27. space stations the FCC licenses, plus non-US satellites granted access to the US market
28. National Telecommunications and Information Administration
29. 40.16°E
30. tested a 10 Gbps laser link to the ground in 2020
31. radio relays
32. reached end of life in November 2017
33. MIT Lincoln Laboratory timeline
34. linked by laser to Alphasat
35. posted on LinkedIn that it had passed 100,000
36. 10 to 100 times more data
37. ITU note
38. streamed video from more than 30 million km
39. 2014 NASA study concept
40. what it calls the first commercial GEO optical data relay satellite
41. standard optical terminals
42. Space Data Network