I liked a lot of the plot elements in 2300AD- the "first-steps-to-the-stars" feel of it, the exotic new worlds, humankind's first meetings with alien civilizations. It was a marvellous creation- but it was founded on some pretty poor science. Intelligent starfaring aliens were all around us, at nearly the same level of development, a highly implausible scenario. The planetology was also a bit wanting; the designers of the game put Earthlike worlds in orbit around some of the most unlikely stars, and practically every habitable planet required some astrophysical anomaly to explain why it was Earthlike. Yes, it's a big universe and undoubtedly there are star systems out there with habitable planets that "shouldn't be there", but when the bizarre and unusual becomes the rule, it makes you wonder what they were thinking.
On the plus side, the history of Earth from 2000 to 2300 AD was carefully worked out and provided a detailed background for the world at the dawn of the 24th century. The stardrive system (the "stutterwarp", a variant of the basic quantum drive) was well-thought out and done with a mininum of hand-waving. It was designed to make only travel between nearby stars feasible, thereby imposing travel routes and choke points and giving local space some character and "geography" that is lacking in many games. I like this approach; you may not, as it forces you to keep track of things in three dimensions. But real space is three-dimensional (at least!), and like it or not, the stars aren't all neatly spaced one parsec apart on a flat hex grid.
The crowning achievement of the 2300AD system were the Kafers- an aggressive alien species at war with humankind. They weren't just aggressive for the sake of being ruthless and inscrutable- their biology and psychology were laid out in detail in "The Kafer Sourcebook", which represents the finest and most detailed example of alien creation in the history of SF roleplaying. While their actions and attitudes might not make sense at first to the players, the GM had access to information that made them believable beings, acting rationally according to their own standards. You don't see that kind of depth very often. While as a professional biologist, I disagree with the premise that a species with the Kafers' sort of intelligence could ever build a starfaring civilization, I have to applaud the thought and effort that went into creating them.
First of all, I decided to start the game off in the mid-to-late 24th century. That would give humans enough time to recover from the overpopulation problems of the early 21st century and develop the stardrive technology they needed to begin colonization of nearby systems. I wanted star travel to be constrained (no flying free through space in just any direction like the Enterprise), and for the actual placement of the stars to be important, and I sat down to think out what the stardrive should be like to achieve this.
After a lot of thought, I settled on a modified jump drive. Like classic Traveller, ships moving between stars systems do so via jumpspace. The basic method involves navigating to a point in the system where it is possible to open a jump point easily, and timing the entry vector into jumpspace so that the ship "coasts" to its destination. I made a number of modifications to the idea, though, to make stellar geography more important. First of all, not all stars are created equal. Their masses differ, and dictate how far into jumpspace their "footprint" extends. If two stars have overlapping "footprints", then a jump between them is possible. The overlap is calculated from the masses of the two stars, and their separation in normal space. Using this system, big stars like Vega and Altair become important crossroads, since they have big jumpspace footprints and touch those of many other stars. Small M-class stars may not connect with more than one or two neighbors, and are not very important in the big scheme of things. I borrowed the idea of jump numbers from Traveller; they range from one to ??? in my game, and do not progress exactly in one-parsec steps. Nor is jump-N a fixed length; it depends on the jump number and the mass of the star as to how far you can go. Each jump number represents a different level of jumpspace, and each level of jumpspace is capable of taking you farther afield- but they are increasingly difficult to open jump points into, and increasingly difficult to navigate through, and there is a law of diminishing returns since the maximum distance goes up roughly as the natural log of the jump number. Current human technology can manage jump-2, with some experimental jump-3 engines.
This is a desirable situation from a gaming standpoint, because the large nexus stars are rare (and therefore will be prime meeting places/points of contention), whereas the small red M stars are everywhere, the vermin of the galaxy, with very rare habitable planets. It makes it possible to ignore virtually all of the uninteresting stars, except for the occasional one that is conveniently located as a stepping-stone to other more desirable real estate. It also reduces the burden of record-keeping for the poor GM, who can reduce about 75% of all stars to quick, bare-bones entries in the star list (name, location, mass, spectral class, end of entry).
Stars don't begin to become well-connected to their neighbors until we get up into the mass range that is suitable for supporting habitable planets (nominally 0.7 to 1.3 solar masses). These make up about 10% of the total in the spiral arms, a more manageable number for the DM. Remember, too, that not all of them will have habitable planets, so we can cross a few more off the list. In the end, you end up paying close attention to perhaps one star in twenty. The rest can remain as background material, undeveloped until you need a plot hook (there are an awful lot of M-class suns out there, and who knows where that pirate base or alien installation may be hidden, just off the main trade routes).
There are two ways to open a jump point- from a shipboard engine, or via a stargate. Stargates are large installations placed in (usually) solar orbit, with very large jump projectors. They open the jump point for the ship, and the ship passes through into jumpspace. It requires a minimal jump engine for "breakout" at the other end; like a chicken's egg, the "skin" of jumpspace is not nearly as strong on the inside as it is on the outside.
