So, I’m writing about the siege of an asteroid base. This asteroid is near the outer edge an asteroid belt at the solar radiation equivalent of Saturn’s orbit from its star (although the raw distance is actually far less, since the star is a smallish K-type). It is an oblong, ~4km x 5km, stony-metallic asteroid.

The base is tunneled into the asteroid’s substrate, and there are relatively few and well-protected entrances/exits for humans. There are also many underground missile silos (missiles are guided; can be explosive or can be small EMPs programmed to attach to enemy ship hulls) and partially underground-mounted anti-aircraft weaponry (microwave pulse weapons, railguns, electrolasers etc.). There are also underground hangars which contain small 1-2 person fighters (armed w/ missiles). Artificial gravity is supplied by the centrifugal force method- The asteroid rotates on its long axis (to provide a greater radius so that it doesn’t have to rotate as fast). Gravity varies from 0.2g-0.9g depending on where you are in the station.

The core of the station houses a small modular helium-cooled fast nuclear reactor similar to the Energy Multiplier Module of today, only better perfected technologically. These are (even irl) very safe reactors because the fire hazard is so low, they require so little maintenance, they cannot melt down in the same way as some other reactors (they simply shut down and don’t work instead of exploding), and they so rarely need refueling. Humans cannot directly access the reactor, but control and monitor remotely from outside the sealed chamber. Waste heat from the reactor is used to heat the station’s outer layers, and to regenerate the CO2 scrubber if needed, on the way to the surface via loop heat pipes.

The atmosphere is maintained with A) Regenerating CO2 removal system similar to the one on the space shuttle, and B) Photosynthetic algae growing hydroponically. Water is recycled wastewater, but there is some backup supply put aside from when the station was dug (water in the tailings was extracted). Food is about 65% farmed insects and fast-growing hydroponic leaf veggies, 35% stored rations (this is a station that normally sees a lot of traffic). Human waste is processed and used for fertilizer; as time goes on they do that with corpses as well.

Now, as for the siege. There are ~18,000 personnel on this station. They are humans, ~50/50% male and female, all trained soldiers via a national universal conscription policy (so, pretty much nobody’s fighting this war by choice), and ~80% between the ages of 16 and 35, although there are some senior officers, medics, and engineers who are older. There are also ~120 extra hydroponics technicians and munitions engineers (also military or military contractors) who had arrived with a shipment of ammo and spare parts/upgrades for some of the systems, and then got stuck there at the beginning of the siege.

Nobody was prepared for a siege. The enemy is fully committed and surrounded the station, where they set up a blockade and shell almost continuously in order to suppress fighters from being sent out, destroy near-surface weapons systems, and disrupt the artificial gravity bad enough that the people inside can’t do anything. They do not want to destroy the station, but capture it more or less intact. They want to force surrender, but they also generally don’t take prisoners. Meanwhile, the defenders are completely unwilling to let the station fall into enemy hands, and if things get bad enough they will self-destruct the station. In fact, when they are finally liberated, their own government destroys the station after evacuating the troops, because they aren’t sure how long they could hold the station and also it’s quite damaged (more resources/time/people/risk to repair it = unfeasible).

The enemy is also in a position to send out ships from the rear and engage any reinforcements that come to liberate the station. Furthermore, although ships here are a good deal faster than modern spacecraft, they are still orders if magnitude below light speed, so friendly reinforcements may take weeks or months to arrive. The enemy also A) Holds the territory near here, so it takes less travel time for them, and B) Has a LOT of fanatically loyal, cheap, quick-maturing troops to draw from.

I’m trying to go for a siege of Leningrad + trench warfare type of vibe. The defenders are stuck here for 3 years, continuously being bombed. Attempts to break the siege are thus limited to sending out small, fast fighter ships that can possibly dodge return fire, and have them drop every bomb and EMP they have within enemy lines. This is usually suicide, and uses up 75% of available fighter craft as well as hundreds of lives. The jarring and weird gravity shifts within the station flings people against walls or kills them with falling objects, and damages systems. Electrical fires happen. People also have to start doing more hazardous work by hand as automated systems get damaged.

Now, with this information, here’s my question. Do you think it would be too hot or too cold as automated systems start to break down, fewer people remain alive to maintain them, etc? Also, do you think fire or disease would be a bigger day-to-day worry? Keep in mind that bathing is mostly out of the question, they are starving, and they have less medicine or sanitation as time goes on. OTOH, explosives + electrical shorts + no ventilation. I need to essentially be able to set a scene and describe how much it sucks from the protagonist’s POV, so I pretty much need a realistic physical/temperature ambiance and rough hierarchy of types of daily survival worries.

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    $\begingroup$ The asteroid rotation generates a centrifugal pull way higher than the gravity pull of the same body. Doesn't this mean that the asteroid will break apart and scatter all around as soon as it starts spinning? $\endgroup$
    – L.Dutch
    Apr 17, 2018 at 7:42
  • $\begingroup$ Depends on the speed of spin and the composition of the asteroid, I’d imagine? If it’s hypothetically possible to do this with spaceships, I can’t imagine it’s not possible to do with an asteroid. Besides, I’d imagine they would’ve reinforced the asteroid and its interior when building the station, $\endgroup$ Apr 17, 2018 at 8:03
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    $\begingroup$ Work out how much energy is required to maintain your habitat (population & industry), as I have the feeling that the 'baked potato' scenario will occur if the enemy takes out the radiators. Even if the reactor has a throttle, you still need power for life support, computers, etc. Perhaps looking up the effect of failure on all of various real world space stations that were put in LEO can give you an idea of what goes wrong. $\endgroup$ Apr 17, 2018 at 8:05
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    $\begingroup$ Spaceships are built to ensure structural continuity. Asteroids not. $\endgroup$
    – L.Dutch
    Apr 17, 2018 at 8:08
  • $\begingroup$ Yeah, but real world space stations are A) not inside rock, and B) not powered by reactors. And they can be too hot or too cold, depending on what went wrong. The radiators are, fortunately, passive heat pipes that don’t require electronic maintenance. Probably they’d be ordered to cut the power as much as possible if cooling elements were getting damaged, which would make the conditions even worse. Also, this type of reactor irl shuts down irreversibly if overheated, and getting it restarted when the thing is modular and sealed is difficult at best. So there’s another issue. $\endgroup$ Apr 17, 2018 at 8:15

4 Answers 4


I think it might not be crazy bad as per your original post.. Probably it should not be if it is to go on for 3 years. Reasons

1: Artificial gravity as you have set up is not some high tech jiggery-pokery but simple centrifugal force. To mess that up the hits would have to alter the rotation of the asteroid. That asteroid is going to have a lot of rotational momentum. A hit hard enough to alter that would probably disrupt the structural integrity of the asteroid.

2: You have a robust internal power source. It sounds like it would be hard to screw that up, and screwing it up would be permanent and the end of the line for the colony.

3: Your people grow their own photosynthetic food. But they are in tunnels. That means they use lights, and so their food is from their power source, which is durable. That is a great system for withstanding a siege. The thing about cities under siege is that they are not food self-sufficient. The besiegers just need to cut food supplies from the surrounding farms and the city will slowly starve. Not this place.

That setup can withstand a 3 year siege. But you have in place the main reason for tension and stress: 18,000 conscripts living together in tunnels and eating bugs and spinach 3 meals a day. That is a lot of young people in very close quarters. The setup is kind of like that of the Walking Dead: zombies are scary threats, but the real horror is other people.

  • $\begingroup$ They are only about 60% food-self-sufficient; this was a frontier guard outpost partly supplied from another asteroid farther in. The attack came at a time when they were in the process of having their targeting systems upgraded, so shit was chaotic and they got taken by surprise. So they will be malnourished and might well starve, particularly if something (heat, fumes, falling debris, etc) kills some or many of their insects. A main problem will likely be the shaking of the asteroid as it is bombed. Objects and people will experience what amounts to earthquake conditions all the time. $\endgroup$ Apr 17, 2018 at 19:02
  • $\begingroup$ Which, if earthquakes are anything to go by, can destroy equipment, start fires, kill people, and so on. Especially when they have a ton of armaments. Fires would be a particularly serious problem. Although, given the stale airplane air, creeping malnutrition, weird (often low) gravity, limited bathing opportunities, possible sanitation issues, and medicine running out, disease could also be a problem. Yeah, I did predict murders, suicides, violence, etc., which in the case of, say, murder or rape are execution offenses. They shoot them in the back of the head (firing squad is waste of ammo). $\endgroup$ Apr 17, 2018 at 19:18
  • $\begingroup$ /This is usually suicide, and uses up 75% of available fighter craft as well as hundreds of lives/ - that is what the criminals are offered. If they make it back, all is forgiven. $\endgroup$
    – Willk
    Apr 17, 2018 at 21:21

Passive heat dissipation with your configuration is going to be troublesome.

Gravity is achieved by rotation of the asteroid, therefore the lightest gases or liquids will tend to move up. Up in this case means toward the center of rotation, which is where the core is located.

So, unless you have some active element to blow away hot air/liquid from the core, you are simply stuffing more heat where it is produced. Overheating in the core is therefore just a matter of time, especially with increasingly damaged machinery and lack of maintenance.

  • $\begingroup$ You’re right, convection within the helium would work ass-backwards in this situation $\endgroup$ Apr 17, 2018 at 13:11
  • $\begingroup$ what about sticking giant copper rod (or better, heatpipe) all the way thorough the center and to radiators? It would be exactly where the hot air delivers its heat, wouldn't it? and would be pretty close to being a passive system. $\endgroup$
    – Mołot
    Apr 17, 2018 at 13:12
  • $\begingroup$ Yup, mentioned heat pipes already. I assumed we’d have heat pipes and liquid droplet radiators. $\endgroup$ Apr 17, 2018 at 13:17
  • $\begingroup$ Now that I think about it, I’d say ditch the EM2 analogue for the reactor and go with a bevy of SAFE-400s. Each one does not produce enough power by itself for a station this size, but they are designed to work and cool themselves in zero-g, they produce less heat, and having multiples will add layers of redundancy if some go down. Yup, ditching EM2. $\endgroup$ Apr 17, 2018 at 13:35
  • $\begingroup$ You should use non-gasses for heat transfer. Something like water, mercury, gallium, or other high heat transfer liquid. Air cooling would be the worst possible choice. Also, since the asteroid is partly made of metal, it could function as a decent heat sink, and the whole surface would act like a radiator. Being at a Saturn like orbit means that the amount of absorbed solar energy should be low. $\endgroup$
    – AndyD273
    Apr 17, 2018 at 17:26

So you want the siege to go on for a while.
So here are some things that are in the defenders favor:

  • The attackers can't try too hard because they don't want to blow up the station, and if they look like they are going to win the defenders will blow up the station.
  • They'd rather the defenders just surrender, but they have no reason to because if they surrender they'll probably die.
  • Likewise, if they were to just say, "hey fine, don't surrender, but we'll let you just escape and fly away" the defenders have no reason not to set booby traps or a delayed self destruct.
  • Heat will be a problem, but possibly not the biggest problem, as they are living in a giant chunk of metal and stone. The iron is a good heat conductor, so if they let the heat get close to the surface they can let it bleed into the iron, and then the entire surface of the asteroid will be their radiator.
  • Food and water probably won't be a big problem at first, as the station would have to be largely self sufficient.

Things that are going against the defenders:

  • The biggest problem will probably be shell shock and the constant mental pressure of being in a confined space with too many people and no way out.
  • Something they really would have to worry about is sabotage. See, any guns/defenses on the surface are going to be taken out quickly, which means there is not much stopping the attackers from landing troops on the surface. The attackers main goal at that point would be to either take control of the self destruct systems so the defenders can't use them, or compromise life support in a way that doesn't raise alarms as unwanted gasses build up and kill everyone.

So if they land, start digging an access tunnel by using the bombardment as cover, set up an airlock to keep station pressure from dropping, then they could potentially get inside the station.

A historical example of this that comes to mind is a story about a fort on the American frontier that was besieged. The attacking group started digging a tunnel, which the defenders could see getting closer to the wall. Fortunately for the defenders it rained, which caused the tunnel to collapse.

The first incursion that happens this way could be a surprise that is stopped in time, but then further incursions would begin to wear down the defenders mental strength, as they are on constant fear of the attackers coming through the walls. The attackers could also work at sabotaging other things such as food production or water recycling, but once again if they are too effective at it looks like the defenders have no hope, they'll likely just self destruct.

  • $\begingroup$ The asteroid is rotating somewhat quickly, the surface terrain is mostly irregular unworked rock, and it’s not a huge asteroid- Large ships would have trouble landing. Ships are not meant to land outside the hangars, which would rarely be open. The anti-aircraft support is not always aboveground (guns get raised and lowered); missiles are in underground silos. That being said, this is one job of the fighter craft, to essentially take up the artillery support slack somewhat when most of the weapons are destroyed or getting repaired. Which costs a lot of lives and ships, obviously. $\endgroup$ Apr 17, 2018 at 19:25

Depends on how much is the internally generated heat vs. how much heat they can dissipate passively. If the reactor and whatever internal systems they have generate more heat that they can dissipate passively, then they would need an active cooling system, and if that breaks down, then obviously it would be hot inside. And in the opposite case, when passive heat dissipation (heat loss would be a more appropriate term in this case) is larger than the heat generated by the reactor and any internal systems (systems where the primary funcion is not heating, heat is released as a byproduct of their primary function) then they would need active heating, and if the systems doing that break down, than it would be cold. Which one is the case with your station is up to you.

Also, fire and explosions would be a larger concern than disease, primarily due to the loss of breathable air. Burning up oxygen, leaking it into space, contaminating it with poisonous materials from smoke or leaking chemicals. And yes, they might have scrubbing systems, plants that generate oxygen, but can those keep up with the heavily increased demand. In your scenario of systems breaking down and massive loss of life, i doubt it. This would be the failing point. Also, fire and explosions are a huge issue on their own, because it is very hard to stop them in such small, crammed, confined spaces with lot's of machines and chemicals that can go boom themselves. Think of chain-explosions. And you have very little means to stop those. You probably have a fire suppression system with a limited amount of coolant. Other than that you only option would be to seal of the parts that are on fire, and went the air, loosing precious oxygen and killing everyone stuck inside.

  • $\begingroup$ The core’s heat dissipation system is passive- Looped heat pipes. It’s also used for passive heating of the station. But I’m sure they’d have a backup active cooling AND heating system. Yeah, I was assuming there’d be areas of the station that were just completely sealed off, vented and unusable due to fires. As food and medicine ran low, I’d think teams in spacesuits would be sent into those to scavenge. Diseases I was thinking mostly malnutrition, but human waste recycled for fertilizer takes power to sterilize. Not enough power? Wear protective gear and pray. Also, crowding and stale air. $\endgroup$ Apr 17, 2018 at 8:31
  • $\begingroup$ Backup systems are just as susceptible to breaking down as primary systems. And for all practical purposes, there is nothing that prevents them from getting destroyed, even before they could be used. Unlike in movies, backup systems are not some magic tools that can make danger go away with the press of a few buttons. $\endgroup$
    – joecro
    Apr 17, 2018 at 8:50
  • $\begingroup$ Well, this station was designed to see and withstand combat, just not this much if it. I’d assume we have looped heat pipes = primary core cooling system/primary passive other area heating system. And then have liquid droplet radiators as more reliable (they are very impact-resistant, smaller, and don’t sit on/near the surface) combat cooling system, at the expense of being able to passively heat non-core areas very well/having less time and space to safely/passively heat CO2 scrubbers to regenerate them. Backup active heat units would probably be good old MMRTGs, which are immortal. $\endgroup$ Apr 17, 2018 at 13:27
  • $\begingroup$ So, no, I don’t think the backup systems are magic- I’d say that they are more durable, and that the primary system might deliberately be taken offline and re-housed (e.g., the heat pipes and radiators are moved away from the surface) when the situation becomes dangerous so that they don’t get destroyed. The backup system (in this case, impact-resistant cooling methods like the LDR) is brought online immediately in combat. There is, in other words, a protocol. Even if unprepared for a siege, first priority would still be to essentially put the station into battle mode to minimize damage. $\endgroup$ Apr 17, 2018 at 13:43

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