Planet-building with the Classic Traveller System
The CT planet building system codifies the world by starport size, planet size, atmospheric composition, extent of oceans (hydrosphere), population, government, law and technology levels. The first four are physical and the last four are social characteristics.
I suppose that Starports can be compared to modern-day airports, if by air was the only way to get from one country to the next. It's not on this planet, but in Traveller the starport is likely the first point of contact between the PCs and a new world. Starports get letter ratings, with higher letters indicating increasingly primitive facilities, with X as the worst meaning no landing facilities of any kind. What can the starport tell us about the planet's inhabitants? In the design sequence, starport rating has a big influence on technology rating, so planets with the best ports tend to have higher tech. Also, better starports have more trade and general contact with the rest of the universe. Remember, even though planets 1&2 are right next to each other on the subsector map, they are still 3 or more light years apart, and very effectively isolated without the presence of starships, and starports at which to land them.
Not that long ago, I discovered something new in the Traveller rules. I was reading Book 3, Worlds and Adventures, and in the section on world design, lo and behold, there was a chart I had never noticed before. I have checked The Traveller Book and Starter Traveller (yes, I own all three rule books – The Traveller Book was a gift from a friend and Starter Traveller I got for free from Drive-Thru RPG [www.drivethrurpg.com]) and it wasn't in either of them. The chart gives a semi-random method for determining the presence of trade routes, based on starport type. Trade routes can give your PCs a reason to visit a world – there will be cargo to buy or sell, patrons to find, or pirates to fight.
Somewhere (I'll remember at some point) I read a suggestion that a planet's population be multiplied by 4% (or less for lower-tech worlds) to determine the number of tons of shipping operating to and from that world. This can be modified based on the starport or tech level, or whatever. If we assume that this figure covers both freight and passenger shipping, now you have an idea of how busy the starport is, and how many ships may be in 'local space' around the planet. This should be conditional upon the quality of the starport. High levels of space traffic will necessitate more port facilities. Also, a planet (particularly balkanized ones, see Government) may have more than one port, but the one in the UPP rating is the highest/best/biggest one.
The next stat in the UPP string is Size. At first glance, all this tells us is the planet's diameter. Right away, this can tell us two things: the surface area, and the relative gravity. A few things can be made of these facts.
Planet Earth is listed in CT canon as being size 8, and we measure gravity from Earth's baseline of 1G. Larger planets (size 9+) will have higher gravity, and smaller worlds will have lower gravity. In the rules section on personal combat there is a table for gravitational effects, showing how different planet sizes affect carrying capacity. Gravity can either be a side-note or a significant plot element, depending on what the PCs will do there. In my short story Just Across Town, the planet's lower gravity becomes important as the protagonists find that they are the strongest people around.
Working from the assumption that all planets are (roughly) spherical, the formula [4*Pi*r^2] will give us the planet's surface area in square km. This will later be affected by the Hydrosphere stat. All other information about the planet's physical shape are left to the referee. Yes, I know later works, Book 6 Scouts and the World Builder's Handbook, go into greater detail, but I don't think that's needed in most cases, except for PCs on survey mission. A few questions you should answer are: how hot or cold is the planet, generally? Is it the only planet in the local system, or are there others? What kind of matter makes up the planet? Are there lots of metals, or few? Will plants grow in the soil, or not? Atmosphere and hydrosphere will influence local flora & fauna but physical composition can be whatever you want it to be.
Atmosphere plays a more significant role in the habitable-ness of a world than size does. Breathing is not optional, so it is important to know what there is to breathe and how much. The atmosphere table lists varying densities of atmosphere, interspersed with contaminants and some alternate compositions. The rules assume that the main components of the atmosphere are nitrogen and oxygen, unless otherwise specified. Thin, Standard and Dense atmospheres can be breathed without assistance, but tainted and exotic atmospheres will need life support gear of some kind. Consult any basic chemistry book and you'll find enough compounds to pollute the air and keep things interesting. If you want to go for the more exotic atmospheres, remember that such planets will have very different flora and fauna from earthlike planets. You can't have daffodils growing on a planet where it rains sulfuric acid.
At the extreme end of the atmosphere table are the non-breathable ones, including the insidious atmosphere which can eat through your protective gear, thereby ending the adventure and ruining the PC's day. The equipment lists give you all the gear your PCs will need to handle the atmosphere issues, but what will they do when the gear breaks or malfunctions? You've got instant adventure, just take away the oxygen. The absence of oxygen or the presence of toxic gases is of enormous importance to anyone spending time out in the open, and while it need not always be a major element of an adventure, the atmosphere should not be ignored. Both the Classic Traveller adventure Shadows and Lois M Bujold's novel Komarr (part of the Vorkosigan series) use the atmosphere as a significant device in moving the plot.
Humans and other carbon-based life forms need water to survive, so it is important to know how much water a planet has. Again, the rules assume that the liquid is water, rather than something else. The hydrosphere table is graduated percentages of the surface covered by water. This figure includes all oceans, lakes, rivers and ponds. Some of it, at the poles, will possibly be ice. Or if you've decided the world is cold enough, all of it can be ice. For each level, the specific percentage can be +/- 5% of the given value. If the atmosphere is unusual enough, it might be another liquid, if the atmosphere is tainted, expect the water to contain the same contaminant.
Any settled area is going to need access to water, so plan on having lots of beachfront property. It almost does not need to be said that the surface area of the planet will be effectively reduced by the presence of bodies of water. The nice thing is that when drawing maps of the planet, just about any arrangement will make sense, so no great cartographic skill is required. All the dry land can be in one large mass, or if it fits the adventure better, the planet can be dotted by volcanic islands. Something to keep in mind is that the extent of the hydrosphere affects the amount of rainfall, and the extensiveness of plant (and therefore animal) life.
There may be plenty of uninhabited planets/moons/asteroids in the universe, but sooner or later your PCs will want to make contact with other people. So let's talk about populations. The population table scales the population in exponentially increasing levels. As such, massively crowded worlds and frontier outposts with less than twenty people are all possible. In many cases, there doesn't need to be much explanation for why people live on this planet. Good starports, breathable air and decent technology are usually reason enough. On the other hand, it is quite possible to randomly generate a world the size of our moon, with almost no atmosphere and no water, that is never the less home to five hundred million people. THAT takes a little explaining. The question that instantly comes to mind when looking at such disagreeable environments is “why does anyone live there?” You as the referee have to give them a reason to do so. Alternately, you can just exercise referee fiat and change the numbers to make it less awful-sounding. I will give my answer to that question at the end of this essay. For now, the population is there, so what are they doing? Trade classification can help with this, and taking into consideration the physical factors of the planet, think of some Earth society that lives in similar conditions, and you've got ready-made society characteristics to work with. Cold weather but breathable air could be turned into Norwegians in space, densely packed domed cities could be likened to Hong Kong or any other big city. Let the physical stats guide your decision but don't be afraid to just make stuff up.
Ah, government. Where would we be without it? The Government table lists various government setups in no particular order, including anarchy, clan/tribe rule, traditional monarchies, straight democracies and even religious dictatorships. Some of the government descriptions may sound strange. I am told that Marc Miller, the main designer of Traveller, studied sociology in college, so his terminology for these types are technical. 'Charismatic' is the one that always threw me. To be brief, there are two general kinds of governments, rule by the one (few) and rule by the many. You can choose to include details of how the government is set up, division of powers, etc or you can just decide on how much the government gets itself involved in peoples everyday life. Here as with populations, we have a wealth of real-world examples to work with. Not every planet should be like 20th-century America, nor like 20th-century Soviet Russia, but those are two possibilities. Any type of government can be corrupt or honest, effective or incompetent, massively in debt or fiscally sound. Decide what will work best for your adventure, and go with it. Keep record of what the government is like, and decide what that means in terms of that planet's interaction with the rest of your universe.
Law level is where most PC groups will at least initially, interact with the government of a world, by breaking the local laws. The Traveller book suggests rolling Law Level or less on 2D to see if the PCs have a run-in with the law. Imagination should be used here as much as elsewhere. To what extent is law enforcement visible or obvious? Is enforcement of the stated Law Level strict or lax? What are the likely consequences of law-breaking? How much do you want this to be a part of the group's adventure? The threat of fines or imprisonment can keep rowdy PCs restrained, or alternately, despotic forces can be used as the 'villain' for the PCs to oppose.
Law Level descriptions focus on permitted weapons, which brings up an important point: if the PCs are allowed to carry guns, then so is everyone else. Don't be afraid to overpower the PCs with well-armed constabulary. Unlike other RPGs where PCs can get blasted with dragon fire and walk away with most of their hit points, in Traveller, even a handgun can be deadly.
Law level can also reflect that world's attitude towards the PCs. Worlds with low LL may be more open and welcoming, preferring to use social pressure (which can itself be quite harsh) rather than laws to keep the peace. However, once the PCs violate local norms, the response may be swift and direct. For an example of this, read H Beam Piper's Lone Star Planet, available from Librivox or Gutenberg. At the other end, worlds with high LL may rely on the presence of law enforcement to maintain the peace and as long as 'no law was broken', PCs can act as they wish. And of course, don't forget the ever-popular 'police state' setup where the government itself has become the enemy of the people.
For a game set in the “Far Future”, Traveller has always been pretty light on the high-tech goodies. For people who are very familiar with the Star Trek and Star Wars franchises, this can make Traveller seem very dated and, well, lame by comparison. Staples of those franchises like lightsabers, transporter beams (teleporters), instant communication across light years and simply gigantic space ships are absent from Traveller. Communication is limited to the speed of travel, ships have to actually land on planets, and most people are armed with projectile weapons. I have seen on the Citizens of the Imperium discussion board numerous discussions of “why do they still have metal swords in the far future?” and “Why are they still using projectile guns? “. Let me say again that Traveller and Star Wars both came out in 1977 – so the two had almost no direct influence on each other, quite apart from the fact that they are two different media, with two different purposes. Traveller gets it inspiration from lots of sources, mostly sci-fi writings from the 1950's through the 1970's. Just to name a few, there's Piper, (mentioned above), Isaac Asimov, Larry Niven, Andre Norton, E C Tubb, Poul Anderson, Robert Heinlien, and the list goes on. It seems to me that most of these writers didn't worry so much about fancy visually-appealing technological widgets (not so important for print media) and instead wrote about ordinary (and sometimes extraordinary) people and the problems they faced. By contrast, the Star Wars and Star Trek films had to put a lot into visual effects, because that's what films do. Plus the pace of story telling is much faster in films or TV shows than in books. That's why even a regular sized book gets made into a miniseries or gets large parts of the story cut out. While it may be visually appealing to watch some bit of technobabble resolve the conflict of the story (yes, Star Trek: The Next Generation, I'm looking at you), it's a lot more dull to read about some piece of equipment doing the hero's job for him. Accuse me of being unfair to films/TV if you will, I'm just saying that Traveller is a lot closer to sci-fi books than it is to sci-fi films.
Striker provides a rule for determining a planet's (or properly a government's) Gross Planetary Product. This is simply the Gross Domestic Product in space. This value can influence or be influenced by the presence or absence of a trade route – it also asks some useful questions. Why does this planet have all this cash? The Striker rule also has guidelines for determining the planet's military budget. I've compared the range in Striker with current real-world military budgets as a % of GDP [see CIA factbook table here: https://www.cia.gov/library/publications/the-world-factbook/fields/2034.html#138] and it seems to track well with the real world. Even without the use of the Striker formula, if you take a look at real-world countries and find one that you want to use as a model, you can give your players an illustration of how well-off or impoverished a planet is.
Once you have your planetary population figure, you can use this number to determine another feature, the inhabited area. Begin with assigning a population density to the world. For example, the average population density of the United States is about 32 ppl/km^2, but this figure varies widely on our planet. (http://en.wikipedia.org/wiki/List_of_sovereign_states_and_dependent_territories_by_population_density) The pop density figure should reflect the conditions on the planet, so look at the atmosphere code. As a guide, the further your planet's atmosphere code is away from six (Standard) the higher the density is likely to be. If the air is breathable, the population can afford to spread out. On the other hand, if the population is confined to sealed or enclosed spaces, they're likely to be all together in a few cities, with few if any outlying villages. Decide if this settled area is all one contiguous blob, or if there are multiple settled areas with unsettled space in between. How long the planet has been settled? The longer a population has been there, the more likely they are to be spread out. Once you're satisfied with the pop density number, just divide the population figure by the density and you have the settled area in square kilometers. Most planets will have significant unsettled and possibly unexplored areas that are prime adventure locations. Off the radar, outside the comm-sat network, there could be partisans, pirates, refugees, almost anything.
Sure, planet Zog has a poisonous atmosphere. But, darnit, we're Zoggians and proud of it! All that has to be explained is why someone came there originally. Just about any explanation will do, from mining the resources, to crash-landing there, to wanting to found a colony free from the oppression of whoever was formerly oppressing them.
In conclusion, I realize, that this can, when you look at it all in one go, seem like a lot of work. The great thing is that you don't have to go to this level of detail with every world, unless you want to. Creating UPP's is quick and easy, just a series of dice rolls and a few tables to consult. Most planets in your universe will just be the UPP string and a spot on the map. Once you are familiar with the how of fleshing out the skeleton, the what becomes much easier. As to the when, this level of detail is only needed when your PC group is going to spend an important amount of time on the planet, outside of the spaceport or their own ship. If you want them to have an adventure on this planet, give it as much detail as the adventure needs, and run with it. Feel free to borrow ideas & concepts from other media, or from real life! With practice, creating details based on the UPP can be done on the fly, for when the PC group goes somewhere unexpected. A little imagination can transform a boring string of characters into an exciting, unexpected, mysterious world for your PC group to explore.