[Space] GURPS Handbook of the Planets

[Agemegos]

A while ago I was working on a game aid to take most of the drudgery out of generating star systems and planets using the star system and world generation sequences in GURPS Space 4e. The project has ground to a halt as a result of unresolved errata on p.117 of Space, and I no longer have any interest in completing it. However, a number of forum members have said nice things about the last beta version, and others seem to want whatever help they can get with the large task of generating a system. So I have decided to make the last beta version, beta21, available on an abandonware basis.

My GURPS Handbook of the Planets is an Excel workbook without macros. It will open and run okay in Open Office and perhaps other spreadsheet programs capable of importing Excel workbooks.

The Handbook implements the Basic and Advanced starsystem generation and planet generation sequences up to the point of calculating economic volume, provided that the user specifies TL and population. A carrying capacity is calculated if the user specifies TL, but population is not calculated. Spaceport class, government type, and installations are not calculated: I decided that those were too specific to setting parameters and GM intentions to be worth troubling with.

The Handbook does implement features of the GURPS Space system generation sequence that allow the user to choose some of the features of the system (e.g. mass, number, and age of the star[s], arrangement of gas giants, mass, orbital radius, and orbital eccentricity of the 'first' gas giant) and have others generated randomly. It also implements features that allow the user to design a planet and insert it into a randomly-generated system, and to choose the basic features of a designed planet and have the details filled in at random. However, the user cannot generate the 'early' features of a planet randomly and then step in to choose later features. And if a designed planet be placed in circumstances where the orbital mechanics dictate that it will be tide-locked, the parameters affected by tidal locking over-ride input parameters.

The Handbook is so designed that the user's chosen "personal user number" and a "system number" for the system are combined to make a seed for the generation of pseudo-random numbers. That means that if the user puts in the same settings at different times, or if two different users put in the same settings, the Handbook will re-create the exact same system.

This version is released as an incomplete beta version, with no warranty as to fitness for purpose. It is an amateurish game aid, unsuitable for commercial use, and you ought not to rely on it for any important purpose.

Known issues

• The interface is a bit clunky, requiring the user to type accurately input that would be better selected from menus.
• An uncorrected erratum in the rule for volcanic activity, which produces division-by-zero errors in the case of star systems with age 0, has been hacked by trapping the errors and assigning the highest level of volcanic activity.
• I could not implement the rule for assigning orbital radii to moons without using a macro, so I arbitrarily chose a different method, in which the orbits of moons are spaced out like those of planets in a star system.
• I have replaced the official method for assigning bodies' initial periods of rotation with one of my own devising, which avoids the misconception that small bodies tend to rotate slower than large ones even when not braked by tides.
• There being no official corrections for the acknowledged errors in the formulas for tides and tidal braking, I have made and used unofficial corrections.
• In the nature of an unofficial improvement, the Handbook makes tide-locked bodies tide-lock to whatever raises the largest component of their tides, rather than their sun or innermost moon.
• Following GURPS Space, the Handbook does not reckon that tide-locked planets and planets with very long days have their habitability diminished by those features, beyond the effect of any reduction of atmospheric pressure and ocean coverage.

Easter eggs

• The Handbook calculates the equilibrium temperature of a planet or moon at aphelion and perihelion in its orbit. This calculation does not take account of the damping effect of the thermal inertia of the atmosphere and oceans, but it does give some indication of the effects of orbital eccentricity.
• The Handbook calculates the level of illumination at the surface of each planet, taking into account the bolometric correction (i.e. taking account of how much of the starlight is invisible IR and UV).
• For the sun and any moons of a planet, and the sun and primary planet of any moon, the Handbook calculates their apparent diameter (how big they look in the sky), their apparent period of rotation, and the amplitude of their contribution to the equilibrium tide.

If anyone who maintains a repository of GURPS material on-line, in some place where players are likely to find it, wishes to put up a copy of this game aid on their site, that is fine with me. If you do so, would you please post an announcement in the forums, for example with a post in this thread.

Important notices

• I do not propose to finish this game aid or to make further improvements or corrections.
  
• GURPS Space is a trademark of Steve Jackson Games, and its rules and art are copyrighted by Steve Jackson Games. All rights are reserved by Steve Jackson Games. This game aid is the original creation of Brett Evill and is released for free distribution, and not for resale, under the permissions granted in the Steve Jackson Games Online Policy.