Radiation and Ship Design

[Timmon26]

Been thinking about radiation effects on ships lately.

Based on screenshots and comments from Nate, we know radiation will be modeled somehow in-game, and will have an effect on kerbals. The VAB UI shows a "center of" symbol for radiation, similar to the ones for gravity, lift, and thrust. This suggests that a major source of radiation will be engines and reactors, namely NTRs, NSWRs, Orions, and fusion engines. So I threw together a sketch of how this might be visualized in the VAB interface:

Spoiler

Here we have the ship from one of the show and tells. I believe that's the mmH vacuum engine, but let's pretend it's nuclear for a bit...

The player will have to have some way of seeing how intense the radiation from this engine will be when it's running, how far the radiation flux reaches, and what other parts the radiation impinges upon. I don't know how granular the devs want the model to be, but presumably it should represent both how radiation intensity falls off with distance and how it can be blocked by parts. At some maximum range, radiation flux should be too weak to bother calculating and simply drop to zero, like air density at the tops of planetary atmospheres.

The obvious way to model this would be to treat radiation as a point light source that illuminates parts and allows them to cast shadows on other parts. The parts have to be somewhat transparent however, to allow for intense radiation to penetrate them. One way to visualize this in the VAB would be to make this "light" visible, illuminating the ship with the radiation source so the player can see which parts are irradiated and which are shielded. The effect would look similar to the light of reentry as we see it in KSP1. Another way would be to show the radiation as concentric sphere overlays, although this could be visually confusing. A third way would be to cut to the chase and color code the parts of the ship according to how much radiation each is receiving, much like the temperature overlay in KSP1.

If parts can block radiation from reaching others, this opens the door to fun design problems. The player has to make sure the parts that bear the brunt of the radiation are the strongest or simplest, and don't contain fragile electronics or squishy kerbals. It also presents an opportunity to include shadow shield parts specifically designed to block radiation from certain directions, perhaps being procedurally modifiable in diameter or thickness. This potentially creates an additional docking challenge, as players must keep each ship in the radiation shadow of the other to avoid either from being irradiated. Parts' radiation opacity may also change over time, as in the case of a fuel tank becoming increasingly transparent to particle radiation as it empties.

Something to consider is the variation in the types of ionizing radiation. Generally radiation comes in either the electromagnetic or particle varieties, with each being more effectively blocked by dense metal plates or lots of low-density stuff (i.e. hydrogen or water tanks) respectively. Most of the radiation the player's technology will produce will be in the form of neutrons and x-rays, so both are an issue. If it were me, I would handwave a bit and consolidate the two together, modeling them as just "radiation", and giving each part a single opacity to both for simplicity's sake. 

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This all raises the question of what radiation actually does to parts or kerbals. 

On the parts front, one thing radiation should do is simply heat parts up. In the case of NTRs this heating is small, but if you consider the detonation point of an Orion drive a "center of radiation", then any parts not in the shadow of the pusher plate would receive flash after flash of radiation until they are heated to the point of failure, first glowing, then exploding.

Another way radiation may damage parts is by neutron embrittlement, where materials are made weaker by exposure to neutron radiation. One way to model this could be to decrease the part's impact or pressure tolerance gradually the longer it is exposed to a radiation source. The part won't be destroyed, but it will become easier and easier to break if collided with.

Thirdly, radiation exposure may cause electronic parts to fail. Random failures are controversial and I tend to think they're not very fun, but if probe cores or science experiments each had a cutoff "rad hardness" or level of radiation flux they can handle indefinitely, so long as it's not exceeded, that would be a good compromise between realism and simplicity for me. A similar "steady-state" model could also apply to neutron embrittlement, with parts weakening under intense exposure, then returning to normal when no longer irradiated, to save the player the headache of parts being permanently reduced to the durability of balsawood, while still imposing radiation consequences...

On the kerbal front, much depends on how the kerbals' skills and abilities are modeled. I doubt cumulative dose would ever kill a kerbal (although heat surely would), but it could cause them to be less effective at their jobs or drain their XP or something. Not much to say here until the devs reveal more.

[starcaptain]

I think the light source method is the most likely method that they'll do, but I suspect that it won't be something updated every frame. Unlike thermal radiation, I don't think it's going to have impacts that will hurt your spaceship as fast as reentry heating could.

But I can imagine the following: 

You're physical-timewarping your vessel from star A to star B, and the radiation meter starts building up on some parts, over the course of weeks or months instead of seconds. It looks exactly the same as the thermal indicator, but a different color. If it "overheats", the part fails.

As for crew exposure, I imagine it'd be a place where crew health bars makes sense. 

[Pthigrivi]

Nice post. I personally like the color coded parts version because thats what you actually care about. Im less crazy about part effects beyond heat, but I think there’s a world in which high radiation could put probe cores into sleep mode until it subsided, and that different cores and habitable modules would have different shielding ratings, maybe tweakable adding weight. 
 

As far as kerbals go I wrote a long post about combining habitation and LS effects into a ship-wide ‘happiness’ rating that effects science output and mining efficiency. Radiation could have a negative and lasting effect on that. Maybe happiness should be tracked by individual kerbals to avoid exploits though? Maybe colonies could have medical bays that cure them? Having played some long saves with 100+ active kerbals I would actually ditch the XP system. Individual management just consumes too much player time and contributes to grind. New skills should be rewards for increased colony population or something and be applied across your program.  But maybe high radiation exposure would suppress some of those abilities?

[SunlitZelkova]

I just hope the Soviet and Russian method of putting reactors on a long boom away from the crew module will work 

[magnemoe]

On 1/17/2022 at 2:41 AM, SunlitZelkova said:

I just hope the Soviet and Russian method of putting reactors on a long boom away from the crew module will work 

Has they used reactors on manned crafts? 
Most hard sci-fi ships and real concept art using nuclear tend to have the reactor or nuclear engines on an long boom with crew compartment in the front. 

[Pthigrivi]

I don't actually let my mod reactors overheat but I do usually attach them radially with a decoupler/sepratron core eject system for RP reasons. 

[Timmon26]

On 1/16/2022 at 8:41 PM, SunlitZelkova said:

I just hope the Soviet and Russian method of putting reactors on a long boom away from the crew module will work 

I mean it ought to. And not just for crew modules but for probe cores and scientific experiments too. The Pioneer probes had their RTGs mounted on booms to keep their radiation from interfering with science instruments:

Spoiler

I'd love to see players do this for gameplay reasons instead of just role-play. Giving nuclear powered parts restrictions on where they can be placed relative to other parts makes for much more interesting game balance than simply making them more expensive or heavy to offset their usefulness. The more I think about it, the more I like radiation as a mechanic, because it will force players to use good design principles organically, in a way that can't be brute forced...

Well, that or everyone just adopts the adage MOAR SHIELDING! to go along with MOAR BOOSTERS and MOAR STRUTS! 

[t_v]

In gameplay clips, we see shielding being used several times. Additionally, on many ships especially with shielding, the communication devices are kept on long booms to the side of craft. Is this to shield them from radiation coming from the craft or to circumvent the shielding which would block communication?

[magnemoe]

21 hours ago, t_v said:

In gameplay clips, we see shielding being used several times. Additionally, on many ships especially with shielding, the communication devices are kept on long booms to the side of craft. Is this to shield them from radiation coming from the craft or to circumvent the shielding which would block communication?

Interesting point who I have not noticed. Now realistically not only the radiation shielding but anything metal will block radio waves so to communicate back to base you would need to get around all the metal. 
So the KSP standard of slapping on an antenna at an protected spot is not realistic but you don't need high bandwidth most of the time. 

[SunlitZelkova]

On 1/18/2022 at 9:24 AM, magnemoe said:

Has they used reactors on manned crafts? 
Most hard sci-fi ships and real concept art using nuclear tend to have the reactor or nuclear engines on an long boom with crew compartment in the front. 

No, but whereas there are a lot of American proposals that don't use a nuclear reactor at all, most Soviet and Russian proposals do, and keep it out on the boom. They also had a preference for nuclear electric engines, so it is nice that more ion thrusters will be added to the game.

19 hours ago, magnemoe said:

Interesting point who I have not noticed. Now realistically not only the radiation shielding but anything metal will block radio waves so to communicate back to base you would need to get around all the metal. 
So the KSP standard of slapping on an antenna at an protected spot is not realistic but you don't need high bandwidth most of the time. 

If they did implement such a feature, that would probably mean we would need some sort of part to ensure that the antenna stays pointed at Kerbin.