[Spaceships] Magnetic Shielding above TL8

[Anthony]

Originally Posted by AlexanderHowl

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.

Originally Posted by DataPacRat

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.

[DataPacRat]

Originally Posted by Anthony

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.

[Anthony]

Originally Posted by DataPacRat

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.

[DataPacRat]

Originally Posted by Anthony

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...

[Anthony]

The regular radiation rules assume gamma rays; low energy nuclei have much worse penetration. 0.2c is only 19 MeV/nucleon, even 0.5c is only 145.

[Say, it isn't that bad!]

Plus, at higher tech levels, radiation shielding can be combined with both radiation medication, and genetic engineering for radiation resistance, tolerance, and recovery.

Resisting +10% more Rems; tolerating a Rem dose +10% higher; and being able to recover from 0.5 Rems per year; would (calculated simply) combine into being able to handle +33.1% more Rems per year. And, if dosage remains below 6.05 Rems per year, you could also slowly recover from Rem overdoses.

[DataPacRat]

Originally Posted by Anthony

The regular radiation rules assume gamma rays; low energy nuclei have much worse penetration. 0.2c is only 19 MeV/nucleon, even 0.5c is only 145.

Is this the source of 'solar flares and planetary radiation belts' getting a rPF*20, due to being 'mostly free electrons and alpha particles' (pB436)?

If so, a factor of 20 doesn't reduce a total accumulated dose of 95B rem by all that much...

Originally Posted by Say, it isn't that bad!

Plus, at higher tech levels, radiation shielding can be combined with both radiation medication, and genetic engineering for radiation resistance, tolerance, and recovery.

Resisting +10% more Rems; tolerating a Rem dose +10% higher; and being able to recover from 0.5 Rems per year; would (calculated simply) combine into being able to handle +33.1% more Rems per year. And, if dosage remains below 6.05 Rems per year, you could also slowly recover from Rem overdoses.

This particular probe is unmanned. It contains a fairly complete genetic library of Earth, and a small robofac that could theoretically eventually build gizmos to build cells from scratch, but during the interstellar voyage proper nothing living needs to be protected.