I want my actors in outer space but I don't want them roaming around freely.

Like, if the actors were in a building, there would be walls, doors, elevators. If they were on a land, there would be ridges, water, cliffs.

In my world, an attacker from another dimension, one where the 3'rd dimension does not exist, is terra-forming (or should I say astro-forming) our 3D universe to sustain their 2D life form because their universe is expiring. Our actors fight these attackers where they pop out and the universe is kinda 2D - so, that's one sort of confinement.

I tried thinking about asteroid belts - lots of rock around to form paths and boundaries.

Any other ideas?



On a larger level, movement in space is determined by changes in velocity, often referred to as deltaV. The more deltaV you have access to, the greater the ability you have to move in space. Changing deltaV determines what orbits you can get to (and whatever is in these orbits). Fro example, if you are orbiting Earth and want to go to Mars, you need to add 4.3km/s to your current velocity (a deltaV change of 4.3km/s). There are other factors that have to be considered, such as planetary alignment, but even if you just randomly blasted from Earth orbit with an additional 4.3km/s, you would end up in the vicinity of Mars orbit (just not near Mars itself).

For your specific purpose, the limiting factors could be the amount of fuel or energy the characters have (imposes a pretty clear upper limit to the amount of deltaV that can be expended). The other factor that you can consider is how quickly this deltaV can be applied. Current spacecraft using powerful, high thrust chemical engines can dump a lot of energy quickly, and make impressive changes in a very short time span. (Since these engines are not very efficient, the total deltaV is actually small, and the amount of time they can fire is limited due to the amount of fuel they can carry). Near future ion and plasma engines apply deltaV much more slowly, so can take months to spiral from the Earth to the Moon, but have high efficiency and can boost pretty much continuously, so over the long haul you build up a lot of speed and can get to the outer solar system relatively quickly. Of course you need to consider slowing down as well....

Much of the detail work can be found on the Artomic Rockets website, particularly here: http://www.projectrho.com/public_html/rocket/enginelist.php

although the rest of the site is an amazing repository of information about virtually everything space related.

As far as finding a good setting is concerned, having the battle take place in the Rings of Saturn will provide a nice visual setting, have particles closely spaced together to give the effect most people associate with "asteroids" from the movies (the real asteroid belt has bodies separated by millions of kilometres), and your intrepid heroes can refuel from the ice in the rings, meaning the battle won't be over after a few hours of combat manoeuvres as they drift helplessly towards Saturn's atmosphere...


Movement in space is not limited primarily by terrain - like Rob pointed out in the comments, asteroid belts are very sparse - but instead by time and resources. A great science fiction short story illustrates this nicely:

The Cold Equations

By law, all EDS stowaways are to be jettisoned because EDS vessels carry no more fuel than is absolutely necessary to land safely at their destination. The girl, Marilyn, merely wants to see her brother, Gerry ... Barton explains that her presence dooms the mission by exceeding the weight limit, and the subsequent crash would kill both of them and doom the colonists awaiting the medical supplies.

In other words, your actors are limited by fuel, engines and orbital mechanics. Adding more weight, weapons or people could keep them from arriving at their destination, or at least delay it (and that could be fatal if they lack life support). They can't just jet around merrily - they have to obey physics and math, and that will restrict their movement and actions far more than anything else.

  • $\begingroup$ I see... So, instead of using "what is not here" as a passable terrain (e.g. "you can pass here because it's not a ridge", I can use "what is here" as a form of confinement (e.g. "you can pass here because there are fuel stations, solar rays to charge from, etc...) Very good. I want to accept this answer - maybe wait for more than one, though :) $\endgroup$
    – DraxDomax
    Jun 30 '15 at 12:18

A popular trick among game devs and authors is the "infinite wasteland" trick:

Go anywhere you please, but when you leave the desired zone, you won't find anything interesting.

In space, this looks like the very realistic concept of seemingly going nowhere forever. Obviously, nobody wants to travel for days outside the zone where there is stuff, especially if they have work to do, so having nothing nearby is a good reason to not go nowhere. Why would you leave?

Another trick is the "leave or get shot for defecting" standard:

You run off, we will point the big guns your way and blow you to Saturn.

This very nicely limits your "actors" to a bubble, or multiple bubbles, which they must not leave, lest they are destroyed. Play any FPS and you will understand. Your commanding officer does not approve of them leaving.

Or you could use the "you drift into space, helpless" trick:

You run out of fuel, and now you're hosed. You float into eternity.

Some resource that you need, eg. sunlight, fuel, O2, runs out because the places/bases where you get more are not in your area. People need "stuff," and if they leave their "stuff spots," they will soon die.

Or maybe just the "random instant failure":

You go outside your zone and then some seemingly random event burninates you.

An "actor" of yours decides to leave and takes a tiny asteroid through the face and dies. This isn't necessarily a limit, however, 'random stuff happens' is a surprisingly common trope that limits people in some way, if not obviously.

And finally, "this is our turf":

This is our spot, and since we are advanced, we have 'death-stuff' for keeping you off.

The aliens, who are terraforming as you said, probably have this idea that you should keep away from their stuff, enforced by alien barriers of your own choosing. In the case of "two-dimensional?" aliens, I would suggest a big steel blade that slices you cleanly into oblivion. But again, choose your own adventure.


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