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ENTR

Deep-space network simulator

One Light-Day

Command a Mars rover and a probe beyond Neptune under real light delay. Ordinary protocols break; design one that doesn't.

Real distances · fictional missions

1 · Pick a destination

Distances are for 00:00 UTC. The room covers 2025–2030.

Destination

Working out today's distances…

2 · Send the plan

The plan

  1. 1 · Drive 10 m
  2. 2 · Drive 10 m
  3. 3 · Drive 10 m
  4. 4 · Photograph the outcrop

Goal: the outcrop 30 m ahead. The crater edge is 40 m ahead.

Presets

Protocol upgrades
Each command carries a number. The craft drops copies it has already seen, and Earth can match an answer that arrives late.
Absolute targets (“go to 20 m”) instead of relative steps (“go 10 m more”). Running a copy again changes nothing.
Send the whole plan once as a DTN bundle. The ground station takes custody, so there is no end-to-end timer, and a node that cannot forward yet holds the bundle instead of dropping it.
The craft checks each move against its own sensors and refuses one that would reach a hazard, without waiting for Earth.
Scenario
Simplified: it sees the craft 12 h of every 24, and its pass ends 10 min after you start. With all three DSN complexes, about 120° apart, there is no gap.
Something the planners could not see. No protocol can fix it; only the craft can react in time.

Model boundaries

Distances are real: the Moon uses NASA's mean distance, Mars and Jupiter come from JPL's Keplerian elements (within 2 seconds of light time of JPL Horizons), and Voyager 1 from a monthly JPL Horizons table with daily samples around its light-day crossing. Light time is distance ÷ c. Everything else is a teaching model: execution is instant, no bits are corrupted, the 30-second timeout and four attempts stand in for everyday client habits, after four failures the naive client reports an error and moves on to the next command, and the single-station scenario assumes a simple 12-hour pass. The craft, plans and hazards are fictional. For Voyager 1 the distance is instantaneous, as in NASA's milestone; a real uplink and downlink differ by a few seconds because Earth and the spacecraft keep moving.

Why this matters on Earth

The same rules hold for payment callbacks, webhooks and leases: a timeout shorter than the real round trip turns every slow answer into a retry, and a retry is only safe when the receiver can tell a duplicate from a new request. Mission Control's retry storm shows the same amplification at millisecond scale.

Open the retry storm

Sources