Just because a game is billed as "interstellar adventure" doesn't necessarily mean you'll get much (if any) more use from it. Much may depend on just how far you really mean to go in your departures from "the usual".
+ Emphasis on exploration: I want to spend most of the time in a space RPG, having adventures in a space ship or on unexplored planets. Visiting space ports, dealing with traders, diplomats and other active colonies should be rare.
Does "Star Trek" ring a bell? Setting aside the Trek-specific stuff, exploration was the fictional mission of the
Enterprise -- and its dramatic mission was to provide a "Wagon Train" (other TV show) kind of setup for interpersonal "adventures in a space ship". One could theoretically find a story in almost any gangway, among the 400 or so people aboard.
Unless one happens to be a geologist, exploring another ball of rock and ice might not be very exciting regardless of what sun it orbits. Life is what's most interesting, and it's no coincidence that SF explorers tend to find new civilizations on those new worlds.
Besides SF and popular science literature, I recommend looking into the GURPS line from Steve Jackson Games. I have not used the rules system in a couple of decades, but continue to find the
supplements of interest.
GURPS Space (2nd ed.) comes especially to mind as covering a
lot of topics in "just enough" detail. If you want more about everything to do with making up worlds to explore, from stellar characteristics to societies, check out
GURPS Traveller: First In.
- No Humanoid vs Humanoid: I don't mind dealing with my fellow species or species with different foreheads every once in a while, but this BETTER not be the prevailing model in my RPG. I want the universe to feel extremely Alien and surprising.
Traveller's basic world generation assumes frequent occupation by humans or similar beings. Population, government, law level and tech level are all oriented to that, and so is even the frequency of breathable atmospheres (which pretty much presumes ecology, probably "terraforming").
Other games with such systems are, in my experience, pretty similar in that regard. What may seem a "wide variety" of biologies and civilizations is actually absurdly homogeneous -- in a way that facilitates "space opera" exploration of perennially
human concerns, and even distinctively "modern" (i.e., this year's) values and issues.
Traveller's animal generation tables are more widely applicable. They give you 15 different ecological niches (in four broad divisions of herbivores, omnivores, carnivores and scavengers). Those affect behavior, speed, numbers and other attributes. You'll get weight in kg, and general combat abilities. Details -- such as the critter's appearance -- are up to you.
+ Low Tech: I mean something akin to the technology in the Firefly series. So no warp drive, jump gates, transporters (ala Star Trek).
For interstellar travel with a light-speed limit, you're necessarily dealing with at least one of:
A) deep time
B) vast energies
C) minds as data
Any one of those by itself, if taken even half seriously, introduces matters orders of magnitude more significant than a "Voyage of the Space Beagle". It both requires and produces changes in society, perhaps even (especially for case C) to something in which we can barely recognize ourselves.
Handwaving some sort of "FTL" allows us to tell stories about
people much like us exploring other worlds. A voyage can take a long time in terms of individual lives, but not so long as to turn it into a "time travel" story. It can be costly enough to be uncommon, without having travelers pack energies that dwarf (and could easily destroy) all the works of our 21st-century civilization. It need involve no state of being too much more exotic than that of astronauts today.
"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is."
- Douglas Adams,
The Hitchhiker's Guide to the Galaxy
Do a little reading about the difficulties we face in planning a mission to Mars. See how many times further it is on average to Jupiter, to Saturn, to Uranus, to Pluto. Consider that sometimes planets are on opposite sides of the Sun. Even with fusion-powered rocketry, crossing a single star system could be quite a trip!
Traveller assumes constant accelerations of 1G or more with its utterly fantastic "reactionless" drives, and at 1G a Terra-Mars trip would average about 2 days. That's already about as far out as "warp drive", and a ship built like the
Millennium Falcon instead of a Saturn V just makes it more so.
The thing is that Han Solo makes some sense with ships like that. He doesn't have to make a
whole lot of sense, because "Star Wars" is in a galaxy far, far away from "hard science fiction" -- but he fits in better than he would with the
Discovery from "2001: A Space Odyssey".
Somewhere in between, perhaps, is a setup that's semi-realistic in terms of interplanetary travel but -- as with Traveller's "jump drive", 2300 AD's "stutterwarp", Larry Niven's "hyperspace", the "jump lines" in Niven's and Pournelle's
The Mote in God's Eye, and other fictional FTL schemes -- allows rapid transit from star to star once some distance from any planets.
