[Spaceships] Habitat observations
 

When I first got Spaceships, I was very impressed, but a little disappointed because it didn't look like you could really design space habitats--the armor rules didn't really cover the kind of massive, thick shielding one needed to protect a population from cosmic radiation over the long term.

But I think I was wrong...

Roughly speaking, you need about one meter of steel (or two meters of loose gravel, soil, etc., or about five meters of ice) to protect people from cosmic radiation over the long term.

You can do it. One meter of steel would correspond to about dDR 280, which is what you get with four levels of steel armor for an SM+15 hull. (You need to apply this to all three hull sections, about 60% of the total mass of the ship.)

(By the way, its not DR that matters but having about 5-7 tons of mass per square meter between you and the radiation of space...any armor would do, probably, but you need four levels of it and a SM+15 hull. I'm not sure if the "four levels" rule would apply to smaller craft...the DR goes down but is that because the armor really isn't as thick? It's still 60% of the overall mass of the craft. It's probably a moot point, though; if you're talking a true space habitat, something you can landscape on the inside for a quasi-Earthlike environment, you usually need at least SM+15 anyway.)

60% of your mass (twelve systems) gives you plenty of room for habitats, open space, solar power (or power plants), factories, hangers, etc. You have a lot of design freedom.

Assuming a ring design, you can probably treat it as a "saucer" to determine actual diameter, so we're probably talking about a 500-meter-wide torus. Not too shabby!

Thank you, Mr. Pulver. :)

Re: [Spaceships] Habitat observations
 

Pulver's previous vehicle design systems were based on vehicle volume, but with GURPS Spaceships he shifted to vehicle mass.

The reason that DR goes up with SM is that as the ship's mass increases, the ship's surface area increases less, i.e. if you make the ship three times as heavy (3000 tonnes instead of 1000 tonnes) the surface area does not increase by a factor of 3, but by a smaller factor, so you get thicker armour per square meter, on the same "mass percentage/mass budget".

Someone with more math will be along shortly, hopefully to elaborate on what I've written rather than saying I'm wrong.

Re: [Spaceships] Habitat observations
 

You're completely right. This is the cube-square law in action, and working in the big guy's favor for once.

Specifically, scaling mass up by a factor of root 10 (the base of the 1-3-10 progression, of course) scales dimension of everything, including the thickness of the armor, by 10^(1/6). Which, with a little rounding, gives you the 10-15-20-30-50-70-100 scaling of armor values.

Re: [Spaceships] Habitat observations
 

Just a thought... would a mini magnetosphere plasma sail have any beneficial effect on protecting versus charged particles?

Re: [Spaceships] Habitat observations
 

An important note - if you put roughly 15 armor modules on a ship, then that's about enough for that ship to be one SM smaller than normal, because armor is more dense than, say, a habitat module (or nearly anythign else).

This allows you to get extremely heavily armored craft - because the armor is over the same area as a ship one SM smaller, each of those armor modules is equivalent to three armor modules of one size smaller. This would make a 300,000 ton ship, which is normally SM+13, SM+12, and allow each of those fifteen modules of steel armor to provide 60 dDR. That means this SM+12 hyperdense ship would have 300 dDR if it were all made from steel - and thus you can have SM+12 ships or stations that have long-term protection from radiation as well.

Re: [Spaceships] Habitat observations
 

Solar flares, probably. High energy cosmic ray primaries, probably not.

Re: [Spaceships] Habitat observations
 

A quick follow-up...

Assuming a diameter of 500 yards (or 450 meters), the spin gravity calculator at...

http://www.artificial-gravity.com/sw...c/SpinCalc.htm

...says you can have an internal gravity of 1 gee with about two rotations per minute (supposedly within the limits of human tolerance). If you want to drop the rotation rate to one rotation per minute, you get about .25 gees.

Re: [Spaceships] Habitat observations
 

ARISE!

Okay, I've been reading up on cosmic radiation. All the many interesting ideas for shielding just don't work so well with the galactic monster rays.

So looking around I came upon this thread.

I'd like to know if my slightly different interpretation is correct.

Air is 14.7 lb per square inch.
Iron is 0.284 or so lb per cubic inch.

This sounds like it would take 49 inches to equate to the same mass as our atmosphere.
This coupled with our planet's magnetic field knocks the cosmic radiation down from 662+/-108 mSv per year it is in interplanetary space to
the 0.3 mSv per year it is at sea level.
A factor of around 2200
(I think the magnetosphere deflects some of the least powerful galactic cosmic rays, but I'm not sure.)

On habitats you can avoid our inevitable yearly exposure to radon of over 2 mSv for Americans.

That right there would allow you have the same background radiation dose as sea level Americans with only 1 over 6 2/3 the shielding.

So a mere 7.35 or so inches of iron or whatever as it's mass that matters. Times 70 for DR using rolled homogenous steel as close enough...
Gets us a mere 515 DR, 52 dDR

Even the hardest realistic future should allow you to drop that down further without any long term health risks.
As it is 50 dDR is a single armor module for SM +14, 3 for SM +13, etc. unstreamlined

Re: [Spaceships] Habitat observations
 

Something that wasn't mentioned in the thread before (because it was not out at the time) is the Radiation section from Spaceships 5 (pg 40-41). It describes some of the hazardous radiation sources found in space, and how to protect against them.

Re: [Spaceships] Habitat observations
 

It works for most games, but it oversimplifies things.
It used dDR even for cosmic radiation and that simply isn't true. It's mass alone that matters for moderate to high energy GCR. Not to mention that at a point even one armor module of anything will perform the same as our entire atmosphere. And my post suggests that that SM is smaller than R.A.W. implies.

Assuming realistic armors. Cinematic ones could have any protective level the campaign calls for.

I have issues with the R.A.W. radiation rules as it would make radiation sickness far too common for a even single week in interplanetary space making the moon landings impossible.

Re: [Spaceships] Habitat observations
 

I'm not sure where you're getting that. The rules in SS5 take account only of the number of systems (excluding low-mass ones like Cargo bays or Habitats) that are protecting the crewed areas.

No argument there. The current rules are a gameable abstraction. I suppose it's rare for a tabletop game to even care about radiation.

Re: [Spaceships] Habitat observations
 

The rules for number of dense modules still only multiplies dDR and divides by 100 for Cosmic Radiation. It makes more advanced armors more effective when only mass matters. Rock is just as good or bad at stopping GCR as super tough diamondoid, not 1/20th.

Re: [Spaceships] Habitat observations
 

When nearly every space game ignores economics and often Relativity and Newton, a pesky thing like near unstoppable GCR seems almost like inconsequential nitpicking.

Re: [Spaceships] Habitat observations
 

There is no mention of DR in that section. The Radiation PF is based solely on the number of massive systems, and does not change for higher or lower tech levels. Now, perhaps the specific values given can be disputed, but the system is using the same method as you are so should at least serve as a solid starting point.

Re: [Spaceships] Habitat observations
 

Oh crud. I misremembered. I apologize for any confusion.

According to my layman's research, its PF 400 or 4 against GCR is equivalent to our atmosphere. That isn't true as 4 would only cut the dose from open space around 700 mSV to 175 far above our 0.3 mSV or 2 to 3 total background radiation. Off by around 100 if we secretly switched Sv for Gurps Rads.

Re: [Spaceships] Habitat observations
 

No worries. I actually started to get nervous that I'd missed something myself. Wouldn't be the first time.

What you've calculated so far sounds convincing, but I'm just a layman too. It may be that Spaceships is using different assumptions about structural strength / density, or that the way our atmosphere absorbs / deflects radiation is more complicated that simple mass.

The issue of astronauts not surviving a round trip to the moon may be more an issue of the radiation sickness rules being unrealistic, or breaking down when dealing with a low dosage over a long period instead of a single large dose.

Re: [Spaceships] Habitat observations
 

Things like OSHA rules use a linear model for radiation safety and the GURPS rules do also. In reality there seems to be a threshold under which it doesn't have an effect. Otherwise places like Denver or people like aircraft crews that spend lots of time with less atmosphere above them would have lots more cancers.

For Apollo part of the radiation safety was launch during low solar flare periods and hope there are no major ones for a week.

Re: [Spaceships] Habitat observations
 

I think their cancer rates are higher, but all things considered cancer is pretty darn rare for an individual over a single year. We tend to measure them in occurrences per lifetime.

Re: [Spaceships] Habitat observations
 

Here's a map showing the rate of fatal cancers per 100,000 lifetimes, for men in the USA, by county. Here is the corresponding map for women. Cancer rates in the Rockies are if anything significantly lower than elsewhere.

Re: [Spaceships] Habitat observations
 

Well GCR are a minor part of background radiation, especially in the U.S. Around 1/10 of all non-profession related radiation.
Radon exposure seems to be the largest section in the U.S. I bet it would take an in depth statistical analysis to determine if the minor differences in ground elevation and subsequent GCR exposure matter for cancer rates.

But recent research seems to point toward medium to high energy GCR posing half the biological danger as initially thought. They tend to pass through too fast to have much effect or destroy the entire cell rather than damage the D.N.A. risking cancer.
For gurps, this means needing only half as much armor to get earth ground levels, a very nice feature for spaceships where ever gram matters.
Remove radon from the environment and you might get lower cancer rates than ours.

Re: [Spaceships] Habitat observations
 

Odd. I can see California having high rates from all the sun worshipers and air pollustion. But what's going on in the northeast? Is maple syrup carcinogenic, or something?

Re: [Spaceships] Habitat observations
 

I thought that the earth's magnetic field was our primary defense against radiation.
That is why Magnetic Shielding seems to be getting a lot of attention

Admittedly, I am not an expert, but this seems like an entirely viable late-TL8/Early TL-9 technology for protecting space-farers.

I do not expect that a series of properly magnetized sections of the hull would prove terribly expensive weight-wise...

Re: [Spaceships] Habitat observations
 

Magnetic fields pull charged radiation toward the poles making for pretty auroras. GCR is just coming in to fast and hard to be tugged out of the way by anything but sheer mass or fields the size of the sun's.

For spaceships, such fields would work best for solar flares. But if you have the mass to protect against GCR, even large flares are little worry.

Re: [Spaceships] Habitat observations
 

The median age of cancer deaths is higher than the median age of the national population. The median age of New England's population is higher than the median age of the national population.

Re: [Spaceships] Habitat observations
 

Then why isn't Florida black as pitch? Is it all the young hot Cubans pulling down the average?

Re: [Spaceships] Habitat observations
 

Has the area had a lot of smokestack industry within the lifespan of people now dying? A high density of motor traffic? Were a lot of buildings insulated with asbestos? Is there a lot of potassium feldspar in the rocks and soil? Is there radon in the basements? Heating with indoor fires? Used the people to smoke? Is there or used there to be a lot of employment in chemical industry? Indoor work with organic solvents?

Re: [Spaceships] Habitat observations
 

The devil/malignancy is in the details.
I remember in the 80s when bad statistics made it seem like power lines caused cancer. And it turned out that poor people live near them and poor people get exposed to nastier environments in general.

Re: [Spaceships] Habitat observations
 

I built a little calculator for the thickness of the structural hull, mass of the hull and contained atmosphere for a rotating cylindrical habitat, as functions of the length and radius, the "gravity" and air pressure, the mass-per-unit-area of the shielding, armour, landscaping, and fittings, and the strength and density of the structural material. It's an Excel workbook with no macros.

Just at the moment the list of possible building materials is a bit incomplete and some of the values for strength questionable.

I put it on Dropbox for review and personal use: https://www.dropbox.com/s/7iilf35hdx...ator.xlsx?dl=0