Steve Jackson Games - Site Navigation
Home General Info Follow Us Search Illuminator Store Forums What's New Other Games Ogre GURPS Munchkin Our Games: Home

Go Back   Steve Jackson Games Forums > Roleplaying > GURPS

Reply
 
Thread Tools Display Modes
Old 03-17-2017, 09:34 AM   #1
DaltonS
 
DaltonS's Avatar
 
Join Date: Aug 2004
Location: Hamilton, Ont. CANADA
Default [Pyramid #3/34] Alt Spaceships: Basement PF?

I'm trying to design a largely underground Mars base using the "Building" rules in Pyramid 3/34: Alternate GURPS Alternate Spaceships p.9-10, and would like to figure out the radiation protection factor (PF) for inhabited "Basement" systems (ie. those that are underground). There are two such systems (including the core) in the upper hull section, with both middle and lower hull sections completely buried. Spaceships 5 p.41 describes calculating PF for systems of a ship in space, but this assumes all hull sections are equally exposed and nothing outside is adding its protection. I would like to be able to calculate cumulative long term exposure based on the following:
Quote:
Average exposure on the surface of Mars is about 1/4 rads per day at the zero datum altitude. <snip> Mars suits cut the dose in half (PF 2), and the habitats used by the first manned missions would be PF 20. Later permanent structures sheltered by bricks and dirt have a PF of 200 or more.
GURPS Mars, page 20
Any help would be greatly appreciated.

Dalton GURPS is about realistic roleplaying, right?” Spence
DaltonS is offline   Reply With Quote
Old 03-17-2017, 10:03 AM   #2
sir_pudding
Wielder of Smart Pants
 
sir_pudding's Avatar
 
Join Date: Aug 2004
Location: Ventura CA
Default Re: [Pyramid #3/34] Alt Spaceships: Basement PF?

It's effectively going to be high enough to not worry about, a yard's thickness of regolith is PF 1,000 and each additional yard of depth would multiply the the PF by a factor of 1,000. Gamma doesn't penetrate very far into the ground.
sir_pudding is offline   Reply With Quote
Old 03-17-2017, 10:58 AM   #3
malloyd
 
Join Date: Jun 2006
Default Re: [Pyramid #3/34] Alt Spaceships: Basement PF?

Quote:
Originally Posted by sir_pudding View Post
It's effectively going to be high enough to not worry about, a yard's thickness of regolith is PF 1,000 and each additional yard of depth would multiply the the PF by a factor of 1,000. Gamma doesn't penetrate very far into the ground.
And neutrons and high energy charged particles aren't very different. A good first approximation is each foot (30 cm), divided by your shield density, cuts radiation to about a tenth. Soils like regolith are somewhere between 1 and 2 g/cm^3, so a yard is somewhere between PF 1000 and 1 million.

If a few tons per square meter of stuff between you and a radiation source fails to cut radiation to survivable levels, you probably need to start worrying about stuff like the radiation melting your shield.
__________________
--
MA Lloyd
malloyd is online now   Reply With Quote
Old 03-17-2017, 11:09 AM   #4
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: [Pyramid #3/34] Alt Spaceships: Basement PF?

Quote:
Originally Posted by malloyd View Post
If a few tons per square meter of stuff between you and a radiation source fails to cut radiation to survivable levels, you probably need to start worrying about stuff like the radiation melting your shield.
You want on the order of 5 tons per square meter for GCR shielding on long term habitats, they're more penetrating than any radiation associated with fusion, fission, or radioactive decay, and you'll get a detectable (but not dangerous unless things are really strange) muon count quite far underground as muons don't have strong force interactions so they don't get stopped by collisions with nuclei, but yeah, underground structures do not generally need to worry about radiation.
__________________
My GURPS site and Blog.
Anthony is offline   Reply With Quote
Old 03-17-2017, 11:30 AM   #5
The_Ryujin
 
The_Ryujin's Avatar
 
Join Date: Jul 2012
Location: A crappy state called Illinois
Default Re: [Pyramid #3/34] Alt Spaceships: Basement PF?

Well, a system worth of protection weights 1/20th of the ships total weight and a cubic foot of soil weights around 92lbs/ft^3 or 0.046tons/ft^3. Figure how much a system weighs for you building then figure how many cubic feet or soil are covering the basement and multiply the cubic feet by 0.046. Divide the weight of the soil by the weight of a building system, that's how many systems of protection the basement has. Finally multiply this product by the PF that one system of protection gives.

Example: A system for a SM+14 building weighs 50,000 tons and a single system of coverage gives PF400. Now let's say that it's basement is covered by 50,000 cubic feet of soil which weighs 2,300 tons. 2,3000/50,000 is 0.046. So this means that 2,300 tons of soil gives PF 400×0.046 or 18.
__________________
GURB: Ultra-Tech Reloaded

Normies: Man! The government is filled with liars and thieves! Me: Well yeah, here's what they're lying about, what they're stealing from you, and who's doing it. Normies: Rolls eyes Shut up conspiracy theorist Me: >.>
The_Ryujin is offline   Reply With Quote
Old 03-17-2017, 11:56 AM   #6
sir_pudding
Wielder of Smart Pants
 
sir_pudding's Avatar
 
Join Date: Aug 2004
Location: Ventura CA
Default Re: [Pyramid #3/34] Alt Spaceships: Basement PF?

Quote:
Originally Posted by The_Ryujin View Post
Well, a system worth of protection weights 1/20th of the ships total weight and a cubic foot of soil weights around 92lbs/ft^3 or 0.046tons/ft^3. Figure how much a system weighs for you building then figure how many cubic feet or soil are covering the basement and multiply the cubic feet by 0.046. Divide the weight of the soil by the weight of a building system, that's how many systems of protection the basement has. Finally multiply this product by the PF that one system of protection gives.

Example: A system for a SM+14 building weighs 50,000 tons and a single system of coverage gives PF400. Now let's say that it's basement is covered by 50,000 cubic feet of soil which weighs 2,300 tons. 2,3000/50,000 is 0.046. So this means that 2,300 tons of soil gives PF 400×0.046 or 18.
18 is at least two orders of magnitude too low.
sir_pudding is offline   Reply With Quote
Old 03-17-2017, 12:04 PM   #7
Anthony
 
Join Date: Feb 2005
Location: Berkeley, CA
Default Re: [Pyramid #3/34] Alt Spaceships: Basement PF?

Quote:
Originally Posted by sir_pudding View Post
18 is at least two orders of magnitude too low.
Well, that's lower than actual shielding, but that might just be because 50,000 cubic feet is a low estimate. It's not totally clear how much area a building is supposed to have, but if we set a SM+14 building to 1,500' long and 300' wide, one foot of shielding is 450,000 cf.
__________________
My GURPS site and Blog.
Anthony is offline   Reply With Quote
Old 03-17-2017, 12:21 PM   #8
The_Ryujin
 
The_Ryujin's Avatar
 
Join Date: Jul 2012
Location: A crappy state called Illinois
Default Re: [Pyramid #3/34] Alt Spaceships: Basement PF?

Quote:
Originally Posted by sir_pudding View Post
18 is at least two orders of magnitude too low.
I was going off of a how Spaceships would handle it. But yeah, the figures in Spaceships is a bit off. It has 50,000 tons of coverage only gives PF400 or PF 8,000 vs solar flares or PF4 against cosmic rays. I wonder if this was supposed to be dPF. Though I should of also treated the building like a core systems doubling the PF.

My example would give negligible FP vs cosmic rays and PF360 vs solar flares (or 720 if treated as a core system). If the PF is supposed to be decade scale then it would give PF 180 (or 360) normally, PF 2 (or 4) vs cosmic rays or PF 3,600 (or 7,200) vs solar flares which isn't as bad.

Anthony: Yeah, I pulled the number out of thin air. With 450,000 cf you'd get PF 166 or PF 3,320 vs Solar Flares. That does seem a bit more in line.
__________________
GURB: Ultra-Tech Reloaded

Normies: Man! The government is filled with liars and thieves! Me: Well yeah, here's what they're lying about, what they're stealing from you, and who's doing it. Normies: Rolls eyes Shut up conspiracy theorist Me: >.>

Last edited by The_Ryujin; 03-17-2017 at 12:27 PM.
The_Ryujin is offline   Reply With Quote
Reply

Tags
mars, pyramid #3/34, pyramid 3/34, spaceships 5

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Fnords are Off
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 06:28 AM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.