[Spaceships] Habitat observations

[Mgellis]

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. :)

[Peter Knutsen]

Originally Posted by Mgellis

(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?

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.

[Ulzgoroth]

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.

[Trachmyr]

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

[Langy]

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.

[Anthony]

Originally Posted by Trachmyr

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

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

[Mgellis]

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.

[Flyndaran]

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

[vierasmarius]

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.

[Flyndaran]

Originally Posted by vierasmarius

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.

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.