I was thinking about games like X-plorers yesterday and got to imagining what it would be like to run a game like that using Tunnels & Trolls. Obviously the first thing you'd need would be the T&T rules.T&T is a classic, especially the 5th ed., so any gamer worth their salt should have a copy. If you don't you can download the abridged free edition from sites like RPGNow or DriveThruRPG.
Then you'll want Garen Ewing's Trolls in Space weapons list. This is what got me thinking about this in the first place. It covers almost all the sf weapons you could want, like Blaster Rifle, Photon Guns and Light Sabres. It also gives you some reference for prices so you can add other equipment, like space suits and whatnot. But sf games are about more than gear. What about the other aspects of the game?
T&T 5th ed. has four basic Character Types, Warrior, Wizard, Rogue and the rare Warrior Wizard. The Warrior can just be renamed to something like "Trooper" and work just fine in a space opera game. Whether he's a Space Marine or a Space Barbarian is detail for the player and GM to work out. The next two types are a little trickier, and my idea is to split them each into two.
The Wizard would become either an "Esper" or a "Scientist". Espers act just like the regular Wizard type, only they've been trained by the Esper's Guild and the spells are renamed as psi powers. For example, "Knock Knock" would be a minor Telekinesis, "Omnipotent Eye" would be Psychometry, etc. Some spells, like Vorpal Blade, the Wall spells, etc. might not be appropriate for Espers and could be omitted. Instead of magic staffs Espers would have psi crystals. Scientists are a little different. They have the ability to use and build build devices that have the same effect as the spells. For example, a Scientist could jury rig a weapon to do double attack dice for one turn, i.e. he "casts Vorpal Blade on it". He could blast an alien with his ice cannon, or "cast Freeze Please". And so on. For Scientists the STR cost of the spell is how many hours it takes them to fabricate the item.
Rogues are handled in a similar manner. They are "Techies" or "Latent Espers". The Latent Espers are just like the standard Rogues in that they can learn psi powers from an Esper. Techies can use supers science items and can learn to build them from Scientists.
Wizard Warriors are "Esper Knights", and are act just as described in the rules. These are the Lensmen and Jedi.
Aliens are pretty easy to handle. To play an alien character just come up with a customized Peters-McAllister chart. For alien beasties just give then a monster rating, or Alien Rating.
But what about space ships? The easiest way would be to treat them similar to monster and give them a Spaceship Rating. For example, a small scout ship might might have a Spaceship Rating of 200 and a blaster turret that does 21D plus adds, while a Space Pirate cruiser might be SR 1000 and have beam batteries that do 101D plus adds. Ships could even have ablative Deflector Screens that are equal to their starting SR and which don't count toward their adds. I'd probably also give each ship a Speed rating to help figure out if you could outrun that Imperial Patrol.
So there you are. Some quick rules to take let your T&T game blast off.