Yags SciFi is a genre specifically designed to allow for space combat, in a way that is interesting for players and suitable for games modelled on science fiction TV, books and films. It is probably slightly harder than the sort of space combat often portrayed by Hollywood, but would be suitable for series such as Babylon 5 or the re-imagined Battlestar Galactica.

Space is big, sometimes it's too big. There isn't much out there between the stars, indeed, there isn't much between the planets either. Any realistic portrayal of asteroid fields is also going to be disappointing to anyone whose expectations have been raised by watching The Empire Strikes Back.

As such, there's not much to fight over in deep space and physics and maths mean that the chances of two fleets meeting up in the middle of nowhere is pretty slim. Most battles are going to be fought close to a planet or similar resource. Even in an asteroid belt, a battle is likely to focus on a single asteroid rather than being fought amongst a cluster of asteroids.

Though the grandfather of science fiction RPGs defines space combat happening at ranges in excess of millions of kilometres, Yags prefers something a bit more personal than a game like Traveller uses. PCs are often skirting the edge of the law, and generally fly small craft that need to run away from big craft (for example, because they're blasting their way off planet, and need to avoid the patrol cruisers in orbit). If the effective range of ships of the line is much more than thousands of kilometres, then a single patrol cruiser can cover an entire planet. Escape is going to be hard.

With effective combat ranges not more than hundreds of kilometres, it becomes possible to dodge most blockades with some careful timing and fast acceleration. It makes it more friendly to PCs.

Space combat is measured in turns of 10 seconds, twice the length of a round in personal combat. This relatively short time period allows for action orientated combat, with characters piloting spacecraft rather than plotting courses and feeding them into a computer.

Even so, there is a conceptual difference between small craft and larger craft - the spacecraft piloting skill becomes less useful the larger the craft being piloted.

Distances in space combat is measured in kilometres. For small craft (e.g., the type PCs are likely to be using), effective ranges will tend to be limited to a few tens of kilometres. This does mean that most targets won't be visible to the human eye most of the time, but you will see points of light, and the occasional glimpse of something more as fighters shoot by.

At this scale, planets are big - effectively borders to the combat zone rather than objects in it. If you want objects to fight around, then they need to be asteroids or comets. The moon Phobos for example is 20km across, though dwarf planets such as Ceres (900km) would be a heavily curved border.

Combat could also occur in an atmosphere (as PCs try to escape from a planet for example), with the atmosphere taking several game turns to clear.

Yags using a logarithmic scale for vehicles, with every 5 points of Size being equivalent to a ten fold increase in volume. This actually allows for very large spaceships without requiring the use of very large numbers to keep track of them.