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Old 12-01-2020, 07:30 PM   #1
DataPacRat
 
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Default [Spaceships] Magnetic Shielding above TL8

I remember once reading that 'cold dense plasma' radiation shielding almost made it into the published version of THS; does anyone have any notes on what sort of stats it would have had? How about the magnetic shield I've heard was in an early draft of Spaceships?


I'm working with a mostly-non-superscience, generally-TL10, somewhat-THS-like, 4e setting, and am looking into options for charged-particle shielding for a space probe. I've hit my limit for simply using mass, and the TL8 version of a Magnetic Shielding field-generator in Vehicles Expansion 1 only goes so far. The best option I can think of so far is to draw on the rules from Vehicles Expansion 2 for an energy-only deflector generator, with a Force Screen Rating of around 3 (9 lbs, 0.45 cf, $4500, 45 kW), but 4e GURPS doesn't really do PD anymore, and it's a bit of a guess for me for how to translate PD into a radiation Protection Factor.


For inspirational reading, I found a 1968 proposal at http://www.minimagnetosphere.rl.ac.u...-29306-386.pdf , and some thoughts from 1975 at https://web.archive.org/web/20081201.../4appendD.html .
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Old 12-01-2020, 07:43 PM   #2
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Default Re: [Spaceships] Magnetic Shielding above TL8

Magnetic shielding doesn't fit very well with the radiation shielding model used in GURPS (it doesn't stop a fraction of particles -- it stops all particles up to a certain energy and none above that, with a fairly small range of energies that are iffy), has a bit odd scaling (energy requirements vary with radius, not area), and requires hazardous field strengths unless very large, so it's probably left out for a reason.
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Old 12-01-2020, 07:44 PM   #3
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Default Re: [Spaceships] Magnetic Shielding above TL8

You need GeV intensities to shield against cosmic radiation and TeV intensities to shield against charged particle beams, so it is not happening outside of super science. It would not protect against EM radiation, neutron radiation, or neutral particle beams, by the way, nor against kinetic energy projectiles.
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Old 12-01-2020, 07:55 PM   #4
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Originally Posted by AlexanderHowl View Post
You need GeV intensities to shield against cosmic radiation and TeV intensities to shield against charged particle beams, so it is not happening outside of super science. It would not protect against EM radiation, neutron radiation, or neutral particle beams, by the way, nor against kinetic energy projectiles.
What I'm actually aiming to protect against are the charged particles that result when a STL craft impacts interstellar atoms at >0.01c. Anything else that gets protected against is gravy.


(About the only non-superscience way I know of to protect against gamma-ray-level EM radiation are to use a high-atomic-weight material, thick enough to absorb secondary impacts; and I haven't been able to make that work with my mass budget. So for this sub-problem, I'm using massively-redundant, fault-tolerant, radiation-hardened computers.)


I've just found a potentially-useful reference; in Ultra-Tech, there's a line that force-fields give an rPF equal to their DR. So an Energy-only screen, which I drop down to TL10, could offer in the neighbourhood of rPF 200 for 25 lbs and $12,500; maybe drop that down to 150 for the TL decrease. Or maybe apply that to Spaceships' force screens.

I'm still open to any other ideas, of course.
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Old 12-01-2020, 07:57 PM   #5
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Originally Posted by AlexanderHowl View Post
You need GeV intensities to shield against cosmic radiation and TeV intensities to shield against charged particle beams.
Eh, most speculation I've seen on charged particle beams was sub-MeV. Of course, it was also atmospheric only and thus entirely irrelevant to spaceships.
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What I'm actually aiming to protect against are the charged particles that result when a STL craft impacts interstellar atoms at >0.01c. Anything else that gets protected against is gravy.
It won't take much to deflect the ionized ISM. Unfortunately, a meaningful fraction is not ionized (estimates seem to range from 10-25%) and won't care about magnetic shielding, nor will dust. Of course, if you limit yourself to less than around .7c you can just use regular matter.
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Old 12-01-2020, 08:04 PM   #6
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Default Re: [Spaceships] Magnetic Shielding above TL8

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It won't take much to deflect the ionized ISM. Unfortunately, a meaningful fraction is not ionized (estimates seem to range from 10-25%) and won't care about shielding, nor will dust.
My reading suggests that a metre of highly-hydrogenized armour (call it Wood or Ice in Spaceships terms; maybe something like pykrete) is a handy way to turn the neutral ISM atoms into separated protons and electrons, and my back-of-the-envelope-figuring from SS5p40 suggests it won't ablate too much from dust on the time-scales I'm interested in.
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Old 12-01-2020, 08:31 PM   #7
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Originally Posted by DataPacRat View Post
My reading suggests that a metre of highly-hydrogenized armour (call it Wood or Ice in Spaceships terms; maybe something like pykrete) is a handy way to turn the neutral ISM atoms into separated protons and electrons, and my back-of-the-envelope-figuring from SS5p40 suggests it won't ablate too much from dust on the time-scales I'm interested in.
If you aren't going to high relativistic speeds it will also make further shielding unnecessary.
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Old 12-01-2020, 08:52 PM   #8
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Default Re: [Spaceships] Magnetic Shielding above TL8

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If you aren't going to high relativistic speeds it will also make further shielding unnecessary.
I've made a rough graph (based on a related graph I found, with very high error-bars, and which may be totally wrong) of how many rem per second have to be dealt with at various speeds:
0.5c: 172,776
0.4c: 18,394
0.3c: 1,958
0.2c: 208
0.1c: 22
0.05c: 7.2
0.02c: 3.7
0.01c: 3.0

Even just 3 rem per second builds up to 95B rem per millennium-long voyage; bringing it down to a more reasonable number would be rather reassuring, and keep those fault-tolerant chips from having to tolerate quite so many faults.


Given that PFs can multiply, I'm now thinking about stacking 5 75-rPF field-projectors in series, which would reduce that 95B dose down to a rather tame 40...
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