TraCSS and EU SST: What Their Joint Study on Sharing Space Traffic Data Shows

When two satellites are predicted to pass close to each other, the operator usually finds out from a conjunction data message, a standardised alert that says how close, when, and with what probability of collision. For years the main free source for most operators has been the US Space Force’s Space-Track service. That is changing. The United States is building a civil system, TraCSS, and the European Union already runs its own, EU SST. Operators can now receive warnings from both.

On 7 October 2026 the Office of Space Commerce announced a joint study, presented at the 2026 AMOS Conference, in which the two systems exchanged data for real satellites and compared what they told operators. The answer matters for anyone writing or complying with space traffic rules, because it shows how far two respected public systems can differ when looking at the same sky.

What TraCSS is and where its mandate comes from

TraCSS, the Traffic Coordination System for Space, traces back to Space Policy Directive-3, the National Space Traffic Management Policy signed on 18 June 2018. SPD-3 said a civil agency should take over the publicly releasable part of the Defense Department’s catalogue and provide collision avoidance support to operators, and that “The Department of Commerce should be that civil agency.” It also said basic US government space situational awareness data and services should be “available free of direct user fees”. Keep that phrase in mind for the funding section below.

According to the joint study paper, TraCSS began serving beta users in September 2024, moved to a production release in March 2026 and opened registration to operators anywhere in the world as pilot users. In June 2026 it added National Government Accounts, read-only access that lets a government see safety information for all spacecraft linked to its country; the United Kingdom and Australia were the first to join. By early August 2026, the paper says, TraCSS had onboarded 68 operators covering more than 11,000 satellites, plus nine national government accounts.

TraCSS screens six times a day and publishes a message for every object that enters a satellite’s screening volume. It does not tell operators what to do. In the paper’s words, it “does not recommend risk mitigation maneuvers”, though it gives operators a contact directory so they can coordinate with each other.

What EU SST is

EU SST is a partnership of 19 EU Member States that tracks objects in orbit and offers three services free of charge: collision avoidance, re-entry analysis and fragmentation analysis. The EU Agency for the Space Programme runs the front desk, and more than 400 organisations receive the services. The collision avoidance work is split between two operations centres, CAESAR in France and S3TOC in Spain, which run in hot redundancy.

The philosophy is different from TraCSS. EU SST picks what it considers the most reliable data for each event and generally publishes only events that reach its WARNING or ALERT thresholds. It does not usually publish close approaches between satellites of the same constellation, on the basis that the constellation operator handles those itself. Unlike TraCSS, it can also recommend a collision avoidance manoeuvre.

What the study did

The two systems registered with each other as authorised third parties, using the delegation features each already offers to operators who hire outside support. They then collected the messages each produced for a common set of satellites between 15 May and 15 July 2026: 39 in geostationary orbit and 58 in low Earth orbit, of which 46 LEO satellites joined from 8 June. Operator names were anonymised.

The numbers

Over the period, TraCSS published at least one message for 63,892 conjunction events and EU SST for 1,432. Only 925 events were common to both. Counting individual messages, TraCSS issued 1,119,385 and EU SST 11,549.

The paper is careful not to treat this as a scorecard. It gives three main explanations:

Starlink. Roughly 90% of the LEO events TraCSS published involved Starlink satellites as the secondary object. The paper’s summary is that about 70% of TraCSS’s LEO events used catalogue ephemerides for Starlink secondaries, which EU SST generally does not publish when better operator-supplied data exist.

Thresholds. TraCSS publishes every close approach; EU SST holds back events below its risk thresholds. That explains 95% of the events in geostationary orbit that only TraCSS published.

Constellation filters. For one GEO operator, 75% of the TraCSS-only events came from just three pairs of satellites in the same fleet, which EU SST would not normally report.

The reverse gap is more interesting. TraCSS published messages for only 65% of the events EU SST published. Most of the EU-only events came from a single GEO operator that, it turned out, had never sent its ephemerides to TraCSS. EU SST was screening that operator’s own predicted positions; TraCSS was relying on the military catalogue. As the authors put it, if one system screens operator ephemerides and the other does not, “the former is more likely to identify conjunctions that the latter misses.”

The case studies make the same point from the other direction. In a GEO example, TraCSS’s catalogue-only messages estimated a miss distance of 18,781 metres at about ten days out, while messages using the operator’s own data put it at 7,562 metres. Once both systems used comparable inputs, their numbers lined up despite using different collision probability methods and different assumed object sizes.

Why this is a legal question, not only a technical one

No treaty obliges an operator to manoeuvre in response to a warning. Article IX of the Outer Space Treaty requires States to act with “due regard” for others and to consult before potentially harmful interference, and Article III of the Liability Convention makes a launching State liable for damage in orbit only if the damage is due to its fault. Fault means falling below a standard of care, and in practice that standard is being shaped by what a reasonable operator does with the warnings available to it. I looked at how that plays out in our piece on who is liable for space debris.

That is why divergence matters. If one public system says a pass is a low-risk INFO event and another calls it a WARNING, which one sets the benchmark? The study does not answer that, but it narrows the problem: much of the disagreement disappears when operators share good data. The growth of debris and large constellations, which I covered in our Kessler syndrome explainer, only increases the number of passes where the question will be asked.

Where regulation is going: mandatory ephemeris sharing

The United States is moving from encouraging data sharing to requiring it. On 22 July 2026 the FCC adopted its Space Modernization for the 21st Century Report and Order (FCC 26-47), which moves satellite licensing into a new Part 100. New section 100.201(c) requires space station licensees and market access recipients to submit “accurate and timely ephemeris data” for all their spacecraft, including propagated ephemeris and covariance for planned manoeuvres, to the 18th Space Defense Squadron and to one or more US space situational awareness systems the Commission identifies. The order encourages updates every eight hours in LEO and every 24 hours above it, and delegates to the Space Bureau the job of naming qualifying providers.

Two points of status. First, the ephemeris rule is not yet in force. The order takes effect 60 days after Federal Register publication, but sections 100.1 to 100.304, which include the ephemeris requirement, wait for Paperwork Reduction Act review, and the Space Bureau is to announce their effective date. As of 22 October I have not found the order in the Federal Register. Second, the accompanying further notice asks whether the Bureau should certify private ephemeris tracking systems, or whether the FCC should name a single provider. TraCSS is the obvious candidate for a public option. This sits alongside the FCC’s earlier move on end-of-life disposal, explained in our piece on the five-year deorbit rule.

Europe is heading the same way. The Commission’s June 2025 proposal for an EU Space Act would require spacecraft operators to use collision avoidance services, including operators from outside the EU that want access to the European market. If both regimes end up mandating data sharing with approved providers, studies like this one become the technical groundwork for mutual recognition.

The funding problem

TraCSS has spent two budget cycles under threat. In July 2025, Payload reported that NOAA’s FY2026 request would have ended federal funding for the programme and cut the Office of Space Commerce to $10 million. Congress did not follow: FedScoop reported in July 2026 that the office’s FY2026 enacted level was $52.5 million and that TraCSS work was continuing on that money. The FY2027 request, though, is $11 million, roughly an 80% cut, and Representative Zoe Lofgren said at a House hearing that it “does not propose funding to continue the TraCSS project.” The office’s director, Taylor Jordan, said the office was looking at a fee-based system or other industry collaboration.

A fee model would sit awkwardly with SPD-3’s commitment to basic services free of direct user fees, though SPD-3 is a policy, not a statute, and could be revised. Executive Order 14369 of December 2025, Ensuring American Space Superiority, lists “effective and responsible approaches to space traffic management” among its goals but says nothing specific about how TraCSS should be paid for.

What I would watch

First, the FCC public notice naming the space situational awareness systems that satisfy section 100.201(c), and the date Part 100 takes effect. Whether TraCSS is named, and whether private providers can be certified, will decide how the US market for these services develops.

Second, FY2027 appropriations for the Office of Space Commerce. If Congress again funds TraCSS above the request, the programme continues as a free public service; if not, expect a fee structure or a handover to industry, and pressure on the free-of-fees principle in SPD-3.

Third, the public products TraCSS has promised: public notifications of emergency-reportable conjunctions, its own satellite catalogue and operator-supplied object sizes for probability calculations. The paper says these are coming in future releases. Each would make TraCSS outputs easier to compare with EU SST’s and more useful as evidence of what an operator knew.

Fourth, the authors’ own follow-up. They say longer and larger studies are under way and that the EU-only events warrant checking that all relevant ephemerides are received and screened. A repeat study after the FCC mandate bites would show whether compulsory sharing closes the gap.

Anuj KumarEditor-in-Chief

Anuj Kumar is the founder of Legal Desire Media and publishes Fashion Law Journal and Space Law Journal.

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