by John M. Ford
John Ford wrote this as commentary / contribution for GURPS Space – but unfortunately, as we fought to get the final manuscript down to "only "112 pages, it didn't make it. So here it is . . . some comments and suggestions for the GM who wants a science fiction campaign set in a single solar system.
Space opera usually spans vast interstellar distances, with dozens or hundreds of inhabited worlds. But it doesn't have to. The exploration of one solar system – ours, or another reached by colony snips – is material enough for centuries of epic adventure.
The one-system background is excellent if the GM and players prefer a "hard science" story. FTL travel is not needed; if the system is not Earth's, it was reached the hard way, by a generation ship, or perhaps by a ship traveling so close to light speed that only a short time passed aboard. Or perhaps FTL exists, but is so expensive that it can only be used to send colonists on one-way trips. Or stargates go only one way. Or the colonists are exiles and can't go home.
The whole campaign can be set at the top end of Tech Level 7. Still, with developments of present-day science technology, this could include better hand weapons, clean fusion plants, a "beanstalk" space elevator from planetary surface to orbit. In particular, this campaign needs breakthroughs in space propulsion. To go somewhere, you must still accelerate a reaction mass and throw out the back of the ship. The mass may be bulky and cheap – water flashed to steam by a nuclear reactor – or dense and expensive – heavy metals. The result is the same: the faster you want to get where you're going, the more of the ship's mass is taken up with fuel.
The cheapest, slowest way to get around in-system is along a Hohmann transfer orbit, an ellipse with foci at the origin and destination worlds. Hohmann data for the Solar System is available in reference books, including the CRC Handbook of Chemistry and Physics, or "Rubber Bible."
Notice we said "slow." A one-way Hohmann trip from Earth orbit to Mars orbit takes about 260 days – and the launch window for a trip this short occurs only once every two years. To travel any faster, or at another time, requires a lot more energy. If the characters aren't to spend most of their lives either on one world or in transit (not that that would be a bad idea), you may want to allow the "torchship," with a highly efficient system that produces 1-G thrust for as long as necessary. 1-G thrust is wonderfully fast; with a mid-course turnover (accelerating halfway, decelerating halfway; it feels just the same aboard ship) you can get from Earth to Mars in less than four days. But this requires power and materials we don't (yet) have, or any useful idea how to make, so it's TL8 at a minimum.
Instead of a star map, the one-system campaign uses an orrery – a set of orbital tracks with markers to show the planet's locations. Move the planets at intervals appropriate to their year; Earth might move every 10 days, Jupiter every year or so. Planetary motions can also be programmed on a home computer, with any level of precision you choose. (One advantage to using the real Solar System is the huge amount of very precise data available, especially for the inner planets.)
One common SF theme is "mining the asteroid belt." This is usually compared to the California gold rush, with lots of lone-wolf miners in their one- or two-person ships, wandering through a cloud of space rocks, staking, digging and jumping claims. Unfortunately, the reality is very different. The asteroids are at least half a million miles apart, invisible from one another. And once you get there, most of them are just rock, and most of the rest are just iron. If civilization needs a lot of asteroidal iron, the cheap way to get it will be to send one mission to find a big lump, and set up a mass driver to bring it slowly home.
If you still want a Belt civilization, you could set up a system with a much denser asteroid belt, or just "salt the mine" with something widely scattered (justifying all those little missions) but very valuable. Metals like iridium, for instance, are much more common in space material than in Earth's crust. Larry Niven posited that "magnetic monopoles" might be the remnants of an inhabited planet, with alien artifacts scattered through it. (Incidentally, our own Belt is almost certainly not a shattered world; there's not enough matter there. Sometimes science is a real spoilsport.)
Given all these restrictions, what sort of adventures can you have in one system? The same sort that real explorers and settlers have always had: The excitement of trying to survive in a strange new environment, making society and government work under new circumstances, and every now and then finding something that no one ever saw before. That's at least as exciting as slaughtering aliens with particle beams.
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