I am waiting for orbital combat. Here is a simplify proposition about how it could work :
Have a set of dots representing the possible positions for ships.
Have five or six concentric circles representing different orbits.
Smaller orbits have fewer dots.
Each turn, ships moves automatically one dot in the orbit they are, in a set direction.
Moving one more circle in any direction costs a token of energy.
Going into lower orbit costs one token, going higher costs two.
Give each ship the ability to launch missiles that obey the same rules and have a set limit of energy.

Correctly done, this means that lower orbits will be completed faster, and that higher orbits will provide with cheaper bombardment.

Increased complexity can be reached by using line-of-sight for laser weapons or for solar recharging the energy.

Hmmm, thinking about it, it could be a good computer game as well :)

One of my favorite tabletop games of all time, Battletech, did space combat in some pretty interesting ways. Its a hex based game, but you might be able to use some of the concepts.

Every unit has a certain amount of thrust points, smaller units had more, making them more maneuverable. They also had a structural integrity rating, showing how much of that thrust they could use in a single game turn without risking damage eg: a ship has 10 thrust but only 8 SI. It may spend 8 thrust every turn without risk, but if it wants to push for that extra 2 thrust in a turn, there is a chance to take damage. Taking damage reduces the SI, so as a ship takes damage, its available maneuvering gets reduced.

There is no friction in space, thus units would continue to move in the direction they are traveling, at the same speed at the start of the next turn(denoted by a small cardboard vector arrow). Acceleration, deceleration, or facing changes all cost a specific amount of thrust points. There is no real max speed, the craft can always spend thrust to move faster, however the size of the play field will limit that to an extent. Trying to hit a target moving fast was more difficult, giving smaller fighter craft a chance to survive and do some damage against larger ships.

Movement starts by determining the units velocity left over from the previous turn. Depending on how fast the unit is moving, it costs more thrust to change facing and move another direction(1 thrust for low speed, 2 thrust for medium, on up to 6+ thrust to turn one hex facing at extreme speeds). Units with more thrust can make more drastic turns, retain velocity better etc, the only downfall is that if you ended a turn moving 8 hexes, the next turn you will move another 8 hexes unless you spend thrust to decelerate.

All ships are also allowed to roll, using 1 thrust point. This exposes different sides of the ship to attack. Especially useful for large ships who could minimize damage on an exposed side, or being better guns to bear on the target.

Anyway, this is getting pretty long, I would suggest checking out any of the Battletech source books that contain the aerospace rules, they might have some good ideas you can adapt to your game!

I designed a spaceship combat board game a while ago now (never released). In this, each ship had an engine and thrusters.

Engines allowed the player to move their ship in the direction it was facing. Thrusters allowed the player to turn the ship.

They had to "charge" the engines and thrusters by using crew to move energy points onto them.

they could only move or turn a number of hexes based on the number of charges spent from that component (and as there was a lot of other components competing for the energy the players had to constantly juggle how they spent their energy from turn to turn).

So if a player wanted to move 3 places forwards and turn three places to the right, they would spend 2 charge points form their engines and then 3 charge points from their thrusters. If they wanted to do more manoeuvring next round, they would need to have enough charge in the components (either unspent or recharged by the crew).

It wasn't realistic movement, but instead an abstract sense of movement to represent how the ships were positioned relative to each other (and obstacles) that was more fun that trying to calculate realistic Newtonian dynamics. :D

Movement in these types of board game is not really about movement at all, but it is about position. Movement rules are just a way of letting your players reposition their piece as part of their strategy. It is the advantages and disadvantages of particular positions that the player is using, so don't make the movement rules too complex.

Also, you need to have a cost associated with repositioning as it is changing the strategy/tactics and this should require some effort/risk/cost (otherwise you make the choice of strategy/tactics an uninteresting/meaningless decision). This is why in my game it cost the player charge to move (which then had the consequence of needing other decisions to be made to get the charge back - it was part of a signalling/bluff part of the game).

So to design your movement mechanics you need to answer 3 questions:
1) What are the advantages that a position can have (not all positions will have these advantages though)?
2) What are the disadvantages that a position can have (not all positions will have these disadvantages though)?
3) What are the costs (effort/risk/costs) to change your position?

Sometimes an advantage can also be a disadvantage. In my game, you could have your ship move behind a planet and this meant that your enemy's ship could not directly target you with a beam weapon. But it also meant that you could not target the enemy with a beam weapon.

You don't want every advantage or disadvantage apply for each position. If you do this, then one position is as good as any other position and so eliminates the need to change positions. Also, by having a variety of advantages and disadvantages, you create a "terrain" that the game takes place in (my trick in my game was to make the advantages and disadvantages of some of the positions change depending on certain factors like the types of weapons on your ship, the types of weapons on the enemy ship, the amount of charge in those weapons - on yours and the enemy - the facing of the ships, etc).

So try and answer those 3 questions. It will help you to work out your movement mechanics better.

Great replies from everyone! Very useful for the design of my simple boardgame.

How should I handle the three dimensional aspects? For example, in 3D space, battleships could roll to change its facing to the opponent. Another example is that while ships could be occupying the same "square" in a 2D grid map, they could be thousands of miles apart in the 3rd dimension (height).

Is it better to ignore them and flatten the battlefield to 2D for simplicity? I am thinking of even taking out the ability to roll so that facing can only be changed by moving or rotating the ship like for real life Navy ships.

Another problem might be that on a 2D surface, if you put rotating gun turrets on the top of the ship (like how guns are mounted on real life naval ships), there is no need to turn: turrets can be rotated to face the opponent's vessel all the time. I was hoping for players to have an incentive to turn and move to let better guns get line of fire.

My take is : ditch 3D. A board is 2D, mapping a 3D space into this is going to be uncomfortable and unrealistic in some way or the other. 3D strategy anyway is not that interesting and usually very complex to visualize, even on a computer.

Yes, turrets would probably cover 360° (and most of a sphere even in 3D) but if your game would be more fun if ships had to turn in order to shoot on rear, just do it. Anyway, in a space combat simulation, you are probably ditching realism somewhere.

However, if you feel like going to the extent of using inertia and turning rules that are similar to navy rules, seriously consider doing a navy game instead (one can make a navy game in a SF setting, see Waterworld for instance)

Taking my game again as a case study:

I was using a hexagonally tiled board for my play field. Because I had decided that turning the ship would be an important part of the gameplay, I set it so that each ship had 6 firing arcs, one for each face of the hexagon.

As the turning angles were also based on the faces of the hexagon, this gave me a simple targeting mechanic.

In a square tiles board, this is not as easy, but it can be done if you allow for overlap between firing arcs (which could be tactically interesting in its own right).

With a free form board (like Warhammer and other table top war games), the actual firing arc does not ahve to be set by any underlying board structure and you can then have these firing arcs as arbitrary as you like, and this could allow you some interesting differences between ship as the various firing arcs can now be one of the differences between them (or even between different weapons).

Remember, one of the first thing you will ahve had to abandon to make a game is reality. You are playing this on a table top, not out in deep space so no matter what you do, it has already been removed from realistic operation right from the start.

So the idea is to give the feeling of space combat that you want to the players and to make it fun. And not be realistic.

If you want the tactics of dealing with firing arcs and it is fun to have them, then you need to add in rules to allow for them. But if it is not fun (maybe because the other rules are too complex), or you just aren't interested in having them, then there is no necessity for you to add them into the game.

In board games, because everything has to be done by the players, you can not make them too complicated. Many board games, although potentially quite fun, fail because they are too complicated for humans to implement. The rules need to be simple and streamlined (that is easy to follow with clear situations where they apply).

Making a 2D board 3D is one place where the rules can become too hard for the player to properly follow. Also, in space, the only real line is the distance between the ship, and this is 1D.

No 3D then.

Two things to discuss:

1) Minimum moving distance - no instant stopping.

What is the difference between allowing ships to be stationary on a turn and forcing them to move a minimum distance? E.g. Battlefleet Gothic rules forces all ship to move a certain minimum distance every turn. Doesn't sound like it affects much

2) Direct fire - Line of sight requirement

Battlefleet Gothic have weapons which do not require line of sight. Their idea is that in space, line of sight can always be achieve by moving up/down in the third dimension. I think I will be going without the line of sight requirement too. This mean that weak support ships can no longer hide behind strong tanks (battleships etc). Does this mean I have to add a range modifier so "healers" (support ship) can effectively hide?

I think an acceleration/deceleration system would work much better than minimum distance per turn, and make more sense. The only question is how much work it would take (for players) to keep track of what each ship moved last turn.

LOS rules add a level of strategy that otherwise is somewhat lost. Maybe if the shot goes through something, damage is halved, or some such ruling? But ultimately, ignoring LOS makes positioning irrelevant, at least in part.