Terminus: Satellite Networking for a Tidally Locked World

An alien AI offers a young civilization on a tidally locked planet a gift: planet-wide access to a large language model, served from orbit. This series is the engineering answer — written as the winning contractor's technical proposal, with every number backed by a reproducible simulation in the terminus simulator. If you would rather see the finished constellation before reading how it was arrived at, the explorer is a live 3D model of it.

The RFP

The alien AI's request for proposals: the planet, the constraints, and sixteen requirements that shape everything that follows.

Know your planet

A world with an eternal sunset belt, a terminator frozen on the ground but turning in space — and why Mercury, whose twilight crawls at walking pace, is a false twin.

The elegant trap

A ring of satellites riding the sunset line forever: perfect coverage, perfect power — and a propellant bill of 3.9 km/s per day that burns the fleet down to 2% in a month.

Shelves of the sky

Surveying every altitude from 300 to 205,000 km: the latency-footprint-dwell tug-of-war, and the Hill-sphere arithmetic that erases the fixed point in the sky.

Rings over twilight

Six polar rings and a 22.4-hour shift schedule — and the simulation that catches the 72-satellite seed leaving towns in silence, then closes the gap with altitude instead of hardware.

Where the mind lives

An LLM's working memory weighs 320 KiB per token. Against satellites that vanish every 11 minutes, that number forces the series' second principle: a handover moves routes, never minds.

Constellation explorer

An interactive 3D model of the whole system — planet, twilight band, six polar rings, and the MEO anchor shell — with live coverage numbers and animated satellite, ring, and anchor handovers.

Talking past a flaring red star

The sun itself broadcasts across 1–3 GHz, poisoning radio's beginner bands. Link-budget arithmetic hands the win to Ka-band pencil beams, with X-band riding shotgun through storms and flares.

Beams, not blankets

Phased-array spot beams collapse a ±460 kHz Doppler search window to a ±6 kHz residual — every beam's spread is the same fixed price, (f/c)·v·β — so the satellite pre-corrects its own motion and parachuted terminals never search for anything. Both ends of the link are flat panels steered by arithmetic, not motors.

First contact

A box wakes in a barley field knowing nothing — no almanac, no clock, no position. An X-band lantern the weather cannot silence finds it in seconds, and it never learns anything that could go stale.

The backbone

Rings never talk to rings: six frozen laser necklaces, feeder links that compute their Doppler instead of searching, and a timing fabric that quietly seats the navigation service beside the minds.

The unbroken thread

A retransmission costs 180 ms; the stall budget is 100. Forward error correction heals losses in zero round trips; ARQ guarantees the rest — and the repair budget breathes with the timetable.

The proposal rests

Volume 1 closes with the truthful ledger: sixteen requirements traced to eight decisions and their reproducible runs — eight designed, five partial, three open and priced into the volumes ahead.

Appendix: the algorithms

The two algorithms that run the network, stated once: how a token routes and how a session picks its anchor — on a schedule computed years ahead, with no poller anywhere and every number traced to a run.