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Old 12-02-2020, 01:04 PM   #21
DataPacRat
 
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Default Re: [Spaceships] Magnetic Shielding above TL8

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Cosmic rays are usually charged (they're heavy nuclei) though they can be very high energy, you want shielding sufficient for multi-gigavolt particles.
Could have sworn I read somewhere that GURPS cosmic rays were mostly gamma. Ah well.

So, this brings us right back to wanting some sort of magshield (or electrostatic field, or whatnot), only omnidirectional instead of focused on particles coming in from the fore. ... I suppose that's a sort of progress.
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Old 12-02-2020, 05:28 PM   #22
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Default Re: [Spaceships] Magnetic Shielding above TL8

Found some interesting references at https://www.centauri-dreams.org/2017...em-and-beyond/ and https://www.centauri-dreams.org/2020...tellar-flight/ . The former is a variant magsail which can be used, among other things, as "Charged particle radiation shield for crewed flights":

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The magnetosphere generated by the engine makes a good radiation shield for the charged particles of the solar wind. It should prove to be a good solution for the solar wind, solar flares and even coronal mass ejections (CME). This device could, therefore, be used for human flight to reduce radiation effects. For human crewed flights, the 1N of thrust is insufficient for the size of the spacecraft and would have a marginal propulsion compared to the main engines. Given the plasma magnetís small size and mass, and relatively low power requirements, the device provides a cost-effective means to protect the crew without resorting to large masses of physical shielding. The plasma magnet would appear to be only effective for the charged solar wind, leaving the neutral GCRs to enter the craft. However, when an auxiliary device is used in the mode of aerobraking, the charge exchange mechanism should reduce the galactic cosmic ray (GCR) penetration (see item 8 below).
The latter is a weird little idea, dragging a kilometres-long superconducting cable to generate an EM field, which as it drags against the ISM, provides electricity which then runs a drive; I'm less interested in the power-generation part than the long, trailing cable generating an interesting field. (Given that I'm focusing on a probe which is plowing a narrow path through space that's clear of particles, and thus a cable pulled along wouldn't ablate particularly fast.)

I'm currently tempted to snag the magsail stats from 3e's Vehicles Expansion 1 (as opposed to the plasma sail stats, which would need an infeasibly-large amount of hydrogen, as it leaks out of the plasma-bubble), claim that the superconducting wire trails the probe instead of forming a loop, and handwave some cosmic-ray PF numbers. Though the less handwaving, the better; anyone care to suggest any details?

(A sample set of magsail stats: TL8, 0.01 lbs thrust: 107.5 lbs, 18,974 kJ, radius 118.5 feet (circumference 744.6 feet), 2.15 cf when reeled in, $10,750, takes 6,955 years to brake a 1-ton probe from 0.01c.)
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Old 12-02-2020, 05:31 PM   #23
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Default Re: [Spaceships] Magnetic Shielding above TL8

The problem with a magsail for an interstellar probe is that it's actually a really really good brake. Which is nice for slowing down at your destination, but not helpful for the trip (thrust is not constant, it varies with the density of the medium and your speed relative to it).
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Old 12-02-2020, 05:35 PM   #24
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Default Re: [Spaceships] Magnetic Shielding above TL8

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The problem with a magsail for an interstellar probe is that it's actually a really really good brake. Which is nice for slowing down at your destination, but not helpful for the trip (thrust is not constant, it varies with the density of the medium and your speed relative to it).
I know; that's why I double-checked how long this prospective magsail would take to brake this probe, which is several times longer than the total trip-time. I just have to nudge up applied thrust a percent or so to compensate.

(A larger magsail would, of course, provide more braking (as well as, presumably, more EM shielding); but I've only got so much available mass to spare inside this probe.)
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Old 12-03-2020, 07:15 PM   #25
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Default Re: [Spaceships] Magnetic Shielding above TL8

By any chance, is there any way to figure out how advanced the technology for "superconductor current capacity" has gotten at THS's tech-level?

I found an article from 1992, at http://www.sjgames.com/gurps/Rolepla.../MagSails.html , which suggests improvements to a magsail's performance-vs-mass as that factor increases. (THS's spacecraft design system only gives stats for plasma sails instead of magsails, with a thrust-to-mass ratio of 1/400.)

I've also found https://web.archive.org/web/20060506...2ad/drafts.txt , which provides a third selection of Vehicles-compatible stats for magsails - and this is the only one which mentions a radiation PF.
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