Diplo Space
Self-guided rehearsal · Diplo Space

The Conjunction Nobody Owns.

September 2019, replayed from the public record: a European science satellite and a satellite from a large commercial constellation converge, with no traffic rule that says who moves and no channel between the two operators but email. You hold the maneuver watch. Four decisions, about ten minutes, every fact sourced. No login, no score.

Self-guided decision rehearsal · ~10 minutes · no login

Take the watch.

September 2019, replayed from the public record. An Earth-science satellite operated by the European Space Agency and a satellite in a large commercial constellation are on converging paths, days out. There is no traffic rule that says who moves, and no channel between the two operators except email. You hold the maneuver watch on the European side. Your choices here are yours; what actually happened is shown at the end, and it is not a grade.

Sources: European Space Agency ↗ · Diplo Space, Inc. ↗

Your seat: collision-avoidance duty officer

You monitor conjunction warnings for the science mission and you can plan and command avoidance burns on your own spacecraft. What you cannot do is order anyone else to move. ESA, describing this event, put it plainly: in the absence of traffic rules and communication protocols, collision avoidance depends entirely on the pragmatism of the operators involved.

Sources: European Space Agency ↗

Ground rules
  • This is an open, low-stress, no-fault rehearsal. There are no wrong answers, only decisions and what they cost.
  • Choosing not to act is a real option, and it is recorded as a finding, not a failure.
  • There are no hidden materials and no trick options.
  • The scenario clock supplies the urgency. There is no countdown and no score: discussion exercises are examined, never graded.
Assumptions & artificialities
  • The timeline and probabilities follow the documented event; sources are listed under every step and in the panel below.
  • Your choices don't change orbital mechanics. They change who carries the decision, and when.
  • Consequence notes describe what the record shows and what your call trades away. They never declare a policy correct.
▸ Every source in this rehearsal (7), with retrieval dates
  • European Space Agency · “ESA spacecraft dodges large constellation,” Space Safety, September 3, 2019. Verified against the loaded source, July 20, 2026. Open it ↗
  • Diplo Space, Inc. · Diplo Space, Field Note 04, “Who Owns the Traffic Lane?” (July 2026), section 6: when coordination fails (our own publication, used for framing). Verified against the loaded source, July 20, 2026. Open it ↗
  • Forbes · Jonathan O’Callaghan, “SpaceX Declined To Move A Starlink Satellite At Risk Of Collision With A European Satellite,” September 2, 2019 (the early probability estimate and the pre-maneuver exchange). Verified against the loaded source, July 20, 2026. Open it ↗
  • SpaceNews · Jeff Foust, “ESA spacecraft dodges potential collision with Starlink satellite,” September 2, 2019. Verified against the loaded source, July 20, 2026. Open it ↗
  • European Space Agency · ESA Space Debris Office, “Collision Avoidance Challenge” (teams alerted about two days before a close approach; final decision typically one day prior). Verified against the loaded source, July 20, 2026. Open it ↗
  • Forbes · Jonathan O’Callaghan, “SpaceX Says A ‘Bug’ Prevented Its Starlink Satellite Avoiding A Collision With A European Satellite,” September 3, 2019 (SpaceX’s statement on the paging bug). Verified against the loaded source, July 20, 2026. Open it ↗
  • European Space Agency · “Automating collision avoidance,” Space Safety / Space Debris. Verified against the loaded source, July 20, 2026. Open it ↗

The event itself is in the record, with sources.

▸ About this rehearsal: type, scope, and what it doesn’t do

Type: a self-guided, single-seat decision rehearsal built on one documented event. In strict HSEEP terms (HSEEP is the U.S. government’s standard for emergency-management exercises), a branching web exercise sits closer to a “game” than a tabletop. We say so because precision about exercise types is part of doing this credibly.

Scope: one seat, four decisions, policy- and coordination-level choices only, ~10 minutes. The timeline and probabilities follow the documented September 2019 event; your choices and notes stay on your device.

What it deliberately isn’t: there is no score, because discussion exercises are examined, never graded. No countdown timer, because tabletops are low-stress by design; the scenario clock supplies the urgency. And no simulated collision on the “hold” path: the record shows what actually happened, and holding is written up as a finding about the system, never a failure of yours.

Want the two-seat version, both operators live on one clock, with a facilitator pushing back? See formats and pricing. Pilots run 90 minutes, $5K–$20K, and you keep the after-action record.

A line we keep in writing

Diplo Space, Inc. is a nonprofit public-interest research and education lab. It uses open-source and public-domain data to translate space-governance regimes into navigable scenarios and exercises for non-specialist officials. It takes no policy positions, accepts no foreign-government funding, and is not affiliated with the U.S. Department of State, the Department of War, or any government agency.