space is an ocean, spaceships are submarines

6 September 2021 § space § game design § setting

  1. I’ve been working on a game about a lonely space traveller.
  2. For the game I am using my homebrew space setting.
  3. People wanted to hear more about my approach to sci-fi, so now you can enjoy this post.

Here’s the main idea:

Spaceships are basically submarines with rocket engines attached.

Here’s why:

With current technology understanding, weapon tech always outpaces armour tech. Flash forward into the future and you get photon torpedoes vs spaceships that are still limited by the weight of their hull plating (no energy shields pls, I want every single shot to carry consequences).

So what you get is space travel that is more like submarines swimming in the ocean. Always trying to detect and go undetected (since being seen would mean almost certain annihilation by the enemy).

This is a long one, so buckle in.


For space submarines to work I am going to make a couple of assumptions about the sci-fi setting we are working with. I will call this the Lo-5” setting:

Now let’s dive into (pun intended) some things we can glean from submarines, and what works differently in space.


Screenshot from Objects in Space (2018), one of the inspirations for the setting

There are two things where I think submarines are similar to spaceships:

  1. Absolutely massive engines compared to the habitable area.

Both submarines and spaceships have to have huge engines per small crew to be able to move fast enough. Your ship is for the most part a weak point and susceptible to being immobilized. Alien (1979) did this kind of thing with the ship design of Nostromo.

  1. Self sustainable, to a point.

Check out the growing veggies in space article by NASA if you want to know more.

Modern submarines don’t ever have to resurface, unless they are refilling food supplies. Same thing is largely true for the ISS, everything is recycled, but growing food is impractical (except for herbs sometimes) due to the amount of space it takes. I imagine in a sci-fi setting having a small greenhouse on your ship would be essential to long duration flights.

However, a key difference is that submarines can afford to have layers and layers of hull plating, while spaceships cannot. When travelling to space, you have to be very considerate of how much weight you are carrying. Every extra gram will reduce your speed and thus, reduce your maximum altitude. Spaceships are fragile.

Visually, this would be a basic spaceship layout:

Two main modules: the engine and the crew compartment, connected by solid beams. Both modules have radiators sticking out.

                       ┌─┐                   │┼┼┼┼│
                       │┼│                   │┼┼┼┼│
                   ┌───┴─┴┐              ┌───┴────┤
       <--     o───┤ crew ├──────────────┤ engine │
                   └───┬─┬┘              └───┬────┤
                       │┼│                   │┼┼┼┼│
                       └─┘                   │┼┼┼┼│

Making good reactors a rarity is also a good incentive to not destroy other ships

I also assume there is a reactor on the ship to generate the needed thrust. Solar panels just don’t have the needed energy output in deep space. However, a reactor with decent efficiency will cost you. Better reactors -> less heat generated -> more rare/expensive. Fusion reactors would probably be legendary in this setting.

The engine/reactor module is separated from the crew for safety reasons. If there is a malfunction or the engine is damaged/leaking, the crew will be separated from it by the vacuum of space if something goes terribly wrong. A weapons module would be located with the engines for the same reasons.

But why are those radiators so huge you ask?

Well, sci-fi media very often misses a crucial aspect of space travel: radiating heat. Without any oxygen around you to take away the heat, it is be absorbed by the ship itself (probably melting it in a couple of spots and definitely not pleasant for the crew). That’s why you need radiators that vent” the heat away in the form of infrared light. I will cover heat and heat management in the next section.


An infrared image of the Hubble space telescope being processed

If you can be seen, you can be targeted. If you can targeted, you can be shot. If you can be shot, you can be destroyed. The easiest way to break the chain of events is at the beginning.

Before we talk about being detected, we need to understand how spaceships would detect other objects.

Submarines use SONAR (which just stands for sound navigation and ranging) to locate various objects in water. They use one of two modes:

Active SONAR: the one most covered by media. It’s the one where the submarine emits a pulse of sound waves and listens for its return. Based on the time it took the sound wave to return and it’s shape” the crew can understand what’s around them. It is used to navigate close to shore where you need precision to not crash into anything.

Passive SONAR: used for the vast majority of a submarines journey. Unlike the active SONAR, you do not emit anything, just listen to what’s around. Ship motors and submarines have a very distinct sound underwater that you can easily detect with this method. It is also great because you do not give away your position when using it.

I imagine spaceships would use a very similar system, except even more reliant on passive scans. Since in space you can actually see what’s around, you do not need the help of active scans for navigation.

active scans are also quite useful in combat, which I cover in later section

BUT, I still think active scans are fun and could be used in specific situations. For example if you are searching for an object that has very low emissions (or none at all) you might use a laser navigation and ranging system (LADAR). Instead of sound waves, it sends light waves that ping back to the ship if they hit an object. However it has the same problem as active SONAR: it basically shouts HEY I’M HERE COME GET ME!” across the whole system.

Which brings me to my next point: EMISSIONS. As i’ve said before: in space light travels far, so if you can emit/reflect no light at all, you are unseen (duh!). And by light I mean the whole spectrum, especially infrared (heat).


Heat is a huge problem in space. Since there is no atmosphere to spread it around, you have to vent it with radiators (those black panels that you can see on the ISS) to not get absolutely cooked by your own life support systems. For stealth it sucks because your 300K radiators stick out like a sore thumb against the 3K of the vacuum of space.

Now this is where I look at submarines to see what they do.

Submarines have to manage sound (instead of heat), so if they want to pass an enemy undetected, they would most likely turn every sound making system on board and go dark”/“go cold”/“drift” until they’ve passed the threat.

In Lo-5 spaceships would do the same thing. Fold those radiators and cool as much of the hull as possible (using cold fuel as one example), turn off the engines and the reactor, then wait until it’s safe. These moments can be great tension builders in your story. I would also make this drifting” time quite short (probably limited by the air supply without life support), something like 100 minutes, a very cinematic number to count down from. Having this short window will hopefully not let the drifting” be too overused by the players, making it both more rare and exciting.

Another one of the most obvious emissions that can be easily detected are rocket engine plumes. When you make any burn to change your vector, you create a massive cloud of heat (and a plenty pf visible light) from the aft of your ship. A long enough burn can also be used by other ships to calculate your mass and future trajectory!

So let’s see how this affects the movement of our space submarine.


The plume of Apollo 8 in Earth orbit performing its burn towards the Moon, as seen from Earth.

Imagine planets at the bottom of gravity wells. Entering and escaping orbit becomes akin to a submarine resurfacing and diving (but upside down).

How would you change trajectory and not be instantly detected? You hide behind something, preferably an asteroid, or even better - a planet. There are specific windows where you can perform manoeuvres without the risk of being detected. Redirecting the ship outside these windows only makes sense in an emergency.

Orbital mechanics is a real headache to track at the table, which is why I try to avoid it (usually space travel is a point-crawl). However, an interesting choice arises because of ships orbits that we have to consider. Do you want to engage your contact in retrograde (opposite rotation) or prograde (same rotation) orbit?

Prograde orbit is the more classic one I would say. You can follow your contact for as long as you need, let your opponent make the first move. But if combat happens, it will be packed with action until one of the ships disengages.

Retrograde orbit would be used if you want to end the combat quickly. Long periods of rest are punctuated by short encounters when all hell breaks loose. It’s like jousting on orbital scales.

A quick diagram (not to scale):

y=you, c=contact, —=plumes

burning behind a planet                    tailing behind a plume

         *  *                                      /
      *        *                                 /           /
 c   *          *                            c <         y <
  \  *          *    /                           \           \
      *        *    y                              \
         *  *         prograde                  | "shadow      |
                        orbit                           zone"

A rocket engine plume also gives an interesting advantage to pursuing ships. The plume creates what’s essentially a shadow zone” behind itself. Since the plume generates a ton of heat, a scanner wouldn’t be able to pick up anything beyond it. If a ship can manage to position itself close enough to the plume without being overheated, it can proceed to tail their target for as long as their engine is burning. This creates some opportunities for tense moments, high risk high reward situations.

After tailing a ship for a while, you may reach a position where you can destroy it…


A still from Battlestar Galactica (1978)

… here are two ways you can do it:

I am not going to touch on ballistic weapons, since they are well explored in other media (The Expanse for one)

  1. Torpedoes

The cool thing about torpedoes is that they can be deployed without your ship leaving stealth. You just have to release it close to your target and then remotely activate it. Just be careful and don’t have it lock on to your own heat signature.

If you are looking to just disable the ship instead of outright destroying it, torpedoes can be equipped with EMP charges, or they can attach themselves to a ship and mess with the engines. These options are great because you can salvage your torpedo and recycle it for future use. This is superb if you are a crew who is running low on budget.

A defence measure against torpedoes would be deploying a decoy. A decoy would emit heat to confuse the torpedo and draw it away from the ship. However, decoys come in limited amounts and are imperfect. If you run out or the decoy is ignored by the torpedo, the situation will go bad really quick.

  1. Lasers

See the problems of laser cutting to get an idea of the process

But what about a GDL? Well, those take a lot of liquid CO2 to function, not the most practical option in space

Lasers are awful because you need to radiate enormous amounts of energy and heat to generate a beam, making you a perfect target for the aforementioned torpedoes.

Lasers are great because they instantly hit your target. The problem is that several thin sheets of reflective material separated by vacuum will be enough to sufficiently slow down the laser getting through the hull.

The only place not defended against light? The sensors of course. This makes lasers the perfect weapons to disable enemy scanning completely. And this can happen to you as well! However, sensors will be tucked away in non-obvious points on the ship. To accurately target a sensor you will have to know your targets ship structure, rotation, trajectory and speed.


The heat generated during the battle can introduce noise to your scans. This makes your information less detailed and targeting less accurate.

To simulate the errors introduced in the heat of battle (the second intended pun, I’m going to hell for this), I am introducing the Noise modifier to your to hit” rolls. In addition to the dice you normally roll to hit, roll dice (d4, d6, d8 depending on your game) equal to the amount of Noise your sensors have. Reduce (or otherwise modify for disadvantage) your to hit roll by the highest Noise die rolled.

Add Noise when:

Add 2 Noise when:

You can remove all noise when you perform an active LADAR scan.

combat procedure

adapted from quadra’s combat flowchart for Mothership

COMBAT BEGINS (someone attacks, there is a time limit etc.)
    └→ retrograde or prograde orbit?
        └→ retrog: short and brutal encounter windows 
        └→ prog: time for recon, then combat every turn
    └→ New turn: calc results, situation is described       ←─┐
        └→ Players declare energy units spent                 │
            └→ Update Noise and Heat modifiers                │
                └→ Perform calculations, burns and attacks    │
                    └→ Is the situation still tense?          │
                         └→ Yes───────────────────────────────┘
                         └→ No: Return to normal time

Notice how both attack options are high risk high reward. I like to keep it this way to have combat be the last resort in this setting. There are lot’s of things that can go wrong and it’s much better (and safer) if you come up with a non-aggressive solution to a problem.

Speaking of solutions…


Analog computer video game (1964)

Remember I mentioned those tubes and cables? Well, they can be used to help you not die in space.


In the world of Lo-5 computers are slow, but they perform incredibly complex tasks that decide between life and death for the crew (which is similar to how Battlestar Galactica does it). Their computing power is limited, so you have decide which calculations you want to prioritize every turn. Information becomes extremely precious when you don’t have the capacity to know everything.

I talk about energy units in a later section about emissions management.

When you want to make a calculation, decide on its complexity. Based on what you choose and how many energy units you are willing to spend, place a counter ticking down every turn until the calculation is done.

A computer’s task can be…

Example: you trying to calculate your own ship trajectory. You are moving close to several big asteroids and a moon at high speeds, so let’s say its a moderate complexity calculation. If you invest 1 token it will take 2/1=2 turns to calculate. 2 tokens - 2/2=1 turn, and so on.

Less than 1 turn is an instant calculation, but remember about the heat generated! Every energy unit you spend on calculation will be converted into heat and raise your chances of being detected (details in the next section).

Here are some possible calculations you might need on a spaceship:

Drift time is how long you can go without venting heat

drift time
own ship trajectory
target identification
target trajectory
target rotation
own ship manoeuvre
active scan
weapons fire
light speed jump

game ideas

Some ways to gamify the setting I’ve outlined above.

1. ship stations

Let’s start with what’s going on inside the ship. The most important thing imho is to give each player a role that is not too overwhelming, and not only useful in a single situation.

I’ve already noted that emissions management is extremely important in space stealth, so let’s explore it some more.

2. emissions management

A good rule of thumb is: the more electricity something consumes, the more heat it will have to radiate away. So the task of energy management is figuring out what systems are crucial at this moment, and what has to be turned off in order to save enegy/heat.

In a game setting I would use several tokens to represent the available energy units from the reactor (let’s say 5 for this example). The role of the engineer would be distributing these tokens between turns and notifying the crew what can and cannot be used. If they decide to cut off navigation, it would better be for a good reason.

Adding several tokens to a system will boost it’s performance. Here is what a spaceship in the process of searching an area would look like:

LADAR has two energy tokens, allowing for higher chances of detecting an enemy ship. Lights are turned off to gain that extra token.

reactor: on | engine: idle
passive LADAR ++ 
navigation +  
computers +
life support + 
lights  -

if you are just cruising in friendly space, I imagine you would be broadcasting a signal to avoid crashing into other vessels.

If the players aren’t actively trying to hide their ship, resolve detection based on common sense. How far away are they from traffic hubs? Does the session call for an exciting moment?

And if the players are actively in stealth mode, here is my detection procedure:

2.1. detection roll

Roll a 2d6 with the following modifiers:

+1 Heat for every energy unit spent on keeping a system active (life support, computers, lights etc.). Could be cool to have different systems cost you different amounts of Heat emitted.

+3 to +9 Heat for a running reactor (depending on its efficiency). If it’s off, systems deactivate automatically if they are not connected to an auxiliary power supply. The engine cannot burn without a reactor on.

Now compare your result with the relevant detection threshold. If your result is over the given value, your ship is detected and hailed, roll for spaceship contacts.

High traffic area (near space ports): detection on a 10+

Medium traffic area (flight routes): detection on a 15+

Low traffic area (system outskirts): detection on a 20+

2d6 spaceship contacts
1 Pirate base
2-4 Pirate hunter
5-6 Interceptor
7 Freighter ship
8-9 Corvette
10-11 Battle cruiser
12 Mothership

Okay, but how do we know what’s going on outside the ship?

3. ranges

This is a way to abstractly visualise space combat without the use of grids. These ranages are based on actual ranges used in submarine navigation.

Draw three concentric circles around your ship. As an option you can also mark sectors within these circles (like forward and aft for instance). Use miniatures or tokens to represent contacts travelling through space. The zones inside those circles will represent the three ranges of your sensors:

  1. Detection range: when something is in this zone, you know it’s there. You won’t know the details, but you can approximate it’s size and trajectory.
  2. Identification range: objects that reach this zone can be identified and scanned.
  3. Targeting range: this is when your sensors can lock onto an enemy and torpedoes will be able to quickly reach their target.
  4. Your ship: if something like a torpedo or an asteroid reaches this area, it hits your ship!

Every turn contacts can move through these ranges, depending on hidden knowledge. The basic movements are:

And that’s all I have for now. Thank you for reading this far! Hope you enjoyed this post, and always feel free to text me on discord or twitter if you want to chat about it.

Stay tuned for my next post in the series: space is an ocean, space stations are islands. In it I will explore Lo-5 star systems in detail: what they look like, how to generate one, how are ladder tables involved in this?

further reading

Throne of Salt - A Layman’s Guide to Hard Sci-Fi - has some great tips on how to further use real world knowledge to deepen your setting.

Atomic Rockets - Detection - a really deep article on stealth in space. It has nice examples from fiction, as well as a great collection of reference images (some of which I used in this post).

Wikipedia - Interplanetary Spaceflight - a good intro to modern propulsion systems that you could use in your game. Also it explains the basic mechanics of moving from planet to planet in an approachable way which is always a plus.