Mapemounde — 2300 AD: differences from the book

Book: 2300 AD: Man’s Battle for the Stars, Marc W. Miller, Timothy B. Brown, Lester W. Smith and Frank Chadwick, Game Designers’ Workshop, 1988. No version or printing number is given; the copy used includes the errata sheet of 19 October 1988.
Rules implemented: The World Generation chapter of the Director’s Guide
Compared against: mapemounde library 0.5.1, as at 9 October 2026

Stars

Stars are generated randomly: the number of stars, their spectral type and size, and the separation of companions. None of this is in the book, which has the referee choose a star from the Near Star List.
White dwarfs are not in the book’s stellar charts. Each is given 0.6 solar masses and a radius of 8,400 km, with a luminosity to match its temperature.

Empty orbits are never rolled, so generation does not stop after two consecutive empty orbits. Instead about 10% of orbits are removed at random and one in six of those becomes an asteroid belt.
That removal happens after orbits are checked for stability and vaporisation, not before.
An orbit is vaporised if its blackbody temperature is 2,000 K or more, calculated directly, not read from the Untenable Orbits table.
The vaporisation and inside-the-star checks count every star in the system, not only the star being orbited.
An orbit beyond three times the distance to a companion is stable only if the companion is lighter than the star being orbited.
Around O, B and A stars, chunks that roll the same orbital radius are merged into one.

Mass and surface gravity are calculated from the world’s diameter and density, not read from the World Mass and Gravity tables.
Atmospheric pressure equals surface gravity in Gs (the condensed table), except that a world with a Vacuum atmosphere has none.
A world that snowballs is given a new Icy density reduced by 10%. The book leaves its density unchanged.
Where the Average Temperatures table gives a range, a single class is used (Cold–Hot becomes Hot).
Ocean and ice sheet coverage is 2D6 × 10%, capped at 100%, so it is never below 20%. The book uses (2D6 − 2) × 10%.
The atmosphere type the book calls “Standard” is named “Moderate”.

A satellite’s radius is capped at 0.8 of its world’s radius, in place of the book’s repeated halving. The cap also applies to chunk satellites.
A satellite over 200 km in diameter that rolls an orbit below 3 is placed at 3. The book rerolls.
A satellite with a size roll below 0 is always a ring, placed in a close orbit.
For satellites whose size falls between or outside the rows of the Minimum Molecular Weight Retained table, the nearest row and column are used, a “vac” entry is read as 120, and a world under 500 km in diameter is a vacuum.