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02-16-2020, 07:30 AM   #21
DataPacRat

Join Date: Nov 2004
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by Agemegos Let's see. 120 parsecs per hour is 4.22 × 10^14 metres per second, and the interstellar medium is around 50 000 000 molecules per cubic metre. Divide by Avogadro's number. Molar mass of hydrogen is two grams. 0.000 07 kg/m²/s. ½mv² = 6.23 × 10^24 watts per square metre. Frontal area of a speedster would be a bit over six square metres. Call that, say, four by ten to the twenty-fifth power joules per second. Spaceships beam damage table. Treat as a neutral particle beam. Four by ten to the nineteenth MJ. Nineteen powers of ten from 3 MJ => nineteen doublings from 3 dice decadal damage. Three million d6 of damage going "dink!" every second.
Let's see; in the local interstellar medium, a speedster can actually hit 450 parsecs/hour instead of 120, so let's multiply that figure by (450/120)^2=14.0625; and multiply it by 10 to convert from decade-scale damage to regular damage; and divide by 100 because the ship is "free" with its Bergenholm active. That works out to an average damage of 14.7M per second... just a hair under half of what the wall-shield provides, meaning said wall-shield doesn't even gain an energy-level when cruising along.

... I think we just discovered how GURPS Lensmans' writers decided how much shielding to put on that speedster. :)

Quote:
 Originally Posted by whswhs Well, an HP. It doesn't have an ST, having no musculature or comparable structures, and its telekinetic ST could be anything. Though I suppose you could estimate it from the force needed to escape from it (if you weren't inside the event horizon).
A possible line of attack: a magnetic field of 16 Tesla is strong enough to levitate a frog (or, presumably, any other organic matter that's subjected to such a field). A 10-15 km radius neutron star's magnetic field, at its surface, is between 10^4 and 10^11 Tesla (with magnetars being 10^8 and 10^11). Making the somewhat unwarranted assumption that the inverse square law applies, then at 242,000 km out (as close as it's safe for the speedster to approach, considering only gravity), then the field would be somewhere around 1/((242,000/10)^2) to 1/((242,000/15)^2) = 1/585,640,000 to 1/260,284,444 as strong, let's say 1/500M. Which would make the magnetic field at that distance 0.00002 to 200 Tesla. Which, making a further unwarranted assumption about diamagnetism, is a force somewhere between 'unnoticeable' and 'exerts 12.5 gravities of acceleration'.

Which looks like I should multiply the minimum safe distance around magnetars by around a factor of, say, four or five.
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02-16-2020, 07:44 AM   #22
whswhs

Join Date: Jun 2005
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by DataPacRat A possible line of attack: a magnetic field of 16 Tesla is strong enough to levitate a frog (or, presumably, any other organic matter that's subjected to such a field). A 10-15 km radius neutron star's magnetic field, at its surface, is between 10^4 and 10^11 Tesla (with magnetars being 10^8 and 10^11). Making the somewhat unwarranted assumption that the inverse square law applies, then at 242,000 km out (as close as it's safe for the speedster to approach, considering only gravity), then the field would be somewhere around 1/((242,000/10)^2) to 1/((242,000/15)^2) = 1/585,640,000 to 1/260,284,444 as strong, let's say 1/500M. Which would make the magnetic field at that distance 0.00002 to 200 Tesla. Which, making a further unwarranted assumption about diamagnetism, is a force somewhere between 'unnoticeable' and 'exerts 12.5 gravities of acceleration'.
Magnets are dipoles, and dipole fields follow an inverse cube law, once you get moderately far away from the source. Closer in, it's something more complicated—I forget the details, but I don't think it's a straightforward inverse square.
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02-16-2020, 07:51 AM   #23
whswhs

Join Date: Jun 2005
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by Agemegos Spaceships beam damage table. Treat as a neutral particle beam. Four by ten to the nineteenth MJ. Nineteen powers of ten from 3 MJ => nineteen doublings from 3 dice decadal damage. Three million d6 of damage going "dink!" every second.
The trick with inertialessness is that collision with a particle never inflicts damage. You just stop dead in space. So what you have to be doing with those fields is not blocking out damage, but shoving the particles to the side so that you can move forward.

If the particles themselves aren't free, then they can't move aside faster than light. If your frontal surface is at a 45° angle, then it has to shove them sideways one km to move forward one km; so you can't move faster than light either. You need a more acute geometry to get multiples of c. Though I don't think Smith had worked out the details, for all that he talked about spherical and other shapes of interstellar craft.
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Bill Stoddard

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02-16-2020, 08:36 AM   #24
Agemegos

Join Date: May 2005
Location: Oz
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by whswhs The trick with inertialessness is that collision with a particle never inflicts damage. You just stop dead in space.
The same is true of beam damage: if you're free and not restrained by a tractor it just bats you away (or did, until the invention of "primaries" so intense that the resistance of the interstellar medium slowed you down enough to be damaged). Indeed, what I'm doing here is demonstrating, from the equivalence of the interstellar medium encountered at high speed to a neutral particle beam. that the immunity in question holds up to half a million d6 damage per second.
Quote:
 So what you have to be doing with those fields is not blocking out damage, but shoving the particles to the side so that you can move forward.
I seem to recall reading of them being smashed or annihilated, but it has been forty years, so maybe you're right.
Quote:
 If the particles themselves aren't free, then they can't move aside faster than light. If your frontal surface is at a 45° angle, then it has to shove them sideways one km to move forward one km; so you can't move faster than light either. You need a more acute geometry to get multiples of c.
120 parsecs per hour is about 3.4 million times the speed of light. A speedster a metre wide to hold a recumbent pilot would have to be 1,700 kilometres long….
Quote:
 Though I don't think Smith had worked out the details,
You don't say!
Quote:
 for all that he talked about spherical and other shapes of interstellar craft.
I think teardrop-shaped superdreadnoughts &c. came from assuming that the resistance of the inert medium would work out equivalent to aerodynamic drag.
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02-16-2020, 11:26 AM   #25
DataPacRat

Join Date: Nov 2004
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by whswhs Magnets are dipoles, and dipole fields follow an inverse cube law, once you get moderately far away from the source. Closer in, it's something more complicated—I forget the details, but I don't think it's a straightforward inverse square.
Does anyone here have any idea how far out the field changes to 1/r^3, or some other way to calculate the field strength at a given distance?

Quote:
 Originally Posted by Agemegos You don't say!
By the by, does anyone have a GURPS formula for dice of damage from a relativistic kinetic-energy weapon? That is, accelerating an object to a measurable fraction of the speed of light before it hits the target?

(Smith only lightly touches on the topic in Lensman, but it seems feasible to use STL thrusters to accelerate a 3-ton impactor up to speed, fire up a Bergenholm generator to place that missile in a 'free' state, and carry it fairly innocuously towards it target before dropping the Bergenholm field and letting those 3 tons regain its previous intrinsic velocity. I'm wondering how fast such an object would have to be to be able to break through the speedster's wall-shield.)
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Last edited by DataPacRat; 02-16-2020 at 11:37 AM.

 02-16-2020, 12:28 PM #26 johndallman   Join Date: Oct 2010 Location: Cambridge, UK Re: Any GURPS stats for black holes, pulsars, etc? When I saw the thread title, my first thought was "Uncontrollable Appetite". The simple calculation for a relativistic collision is a Slam, per p. B371. The speed of light is about Move 3.3*10^8, so an impactor does 3,300,000 dice of damage, call it ten million HP, per hit point it has. This probably underestimates the damage. __________________ The Path of Cunning. Indexes: DFRPG Characters, Advantage of the Week, Disadvantage of the Week, Skill of the Week, Techniques. Last edited by johndallman; 02-16-2020 at 12:33 PM.
02-16-2020, 12:29 PM   #27
awesomenessofme1

Join Date: Mar 2016
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by DataPacRat By the by, does anyone have a GURPS formula for dice of damage from a relativistic kinetic-energy weapon? That is, accelerating an object to a measurable fraction of the speed of light before it hits the target?
Wouldn't that just be conventional collision rules? Speed of light is about Move 327,000,000, so just multiply mass HP by 3,270,000 (or whatever fraction you want to use) and that's how many dice to use.

02-16-2020, 01:17 PM   #28
DataPacRat

Join Date: Nov 2004
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by johndallman When I saw the thread title, my first thought was "Uncontrollable Appetite". The simple calculation for a relativistic collision is a Slam, per p. B371. The speed of light is about Move 3.3*10^8, so an impactor does 3,300,000 dice of damage, call it ten million HP, per hit point it has. This probably underestimates the damage.
Quote:
 Originally Posted by awesomenessofme1 Wouldn't that just be conventional collision rules? Speed of light is about Move 327,000,000, so just multiply mass HP by 3,270,000 (or whatever fraction you want to use) and that's how many dice to use.
Ah, nice and simple.

... Of course, I'm going to be an annoying physics fan and complicate it up a bit, because relativity is fun. I think I'll take a reasonably high, not-particularly-relativistic speed, like 0.6c, as a baseline for damage (that is, ObjectHP * 196,200,000d), and for higher speeds, use the ratios of the Lorentz factors instead of straight speeds. That is, 0.6c has a Lorentz factor of 1.250; so an object travelling at a speed of Lorentz 2.5 would do double the damage - that's around 0.915c; a Lorentz of 10 (0.995c) eight times; a Lorentz of 100 (0.99995c) eighty times, and so on. (Or, to make it one step simpler, set damage as ObjectHP*LorentzFactor*156,960,000d.)

Now, since we're dealing with a Wall Shield of DR 30,000,000 (which I'm assuming can deflect relativistic-level masses as well as it can gamma rays), and assuming an average damage roll, then a 1-hp object (a 1/512 lb or 0.9 gram homogeneous rock) going at Lorentz 0.05 (1/25th 0.6c's baseline L1.25, meaning 0.024c) would do around 27M damage, enough for the shields to sit up and take notice but not quite let damage through. And a 2-hp object (a 1/64 lb or 7.1g rock) would only have to be going half that speed, and so on. 2.4%c... isn't really all that much; the speedster itself can accelerate itself up to that intrinsic velocity in only 38 minutes.

It looks like the safe zone around a body with ridiculously-high gravity may be more a matter of how fast the local rubble might have been accelerated to, rather than strictly due to the dangers of the body itself. After all, I seem to recall that the fastest-spinning known neutron star twirls at 0.24c, so any tiny bits that get flung off for whatever reason (such as a random rock dropping down onto its surface and disturbing its equilibrium) are going to be moving at quite a clip...
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Thank you for your time,
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DataPacRat
"Then again, maybe I'm wrong."

02-16-2020, 01:24 PM   #29
awesomenessofme1

Join Date: Mar 2016
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by DataPacRat Ah, nice and simple. ... Of course, I'm going to be an annoying physics fan and complicate it up a bit, because relativity is fun. I think I'll take a reasonably high, not-particularly-relativistic speed, like 0.6c, as a baseline for damage (that is, ObjectHP * 196,200,000d), and for higher speeds, use the ratios of the Lorentz factors instead of straight speeds. That is, 0.6c has a Lorentz factor of 1.250; so an object travelling at a speed of Lorentz 2.5 would do double the damage - that's around 0.915c; a Lorentz of 10 (0.995c) eight times; a Lorentz of 100 (0.99995c) eighty times, and so on. (Or, to make it one step simpler, set damage as ObjectHP*LorentzFactor*156,960,000d.) Now, since we're dealing with a Wall Shield of DR 30,000,000 (which I'm assuming can deflect relativistic-level masses as well as it can gamma rays), and assuming an average damage roll, then a 1-hp object (a 1/512 lb or 0.9 gram homogeneous rock) going at Lorentz 0.05 (1/25th 0.6c's baseline L1.25, meaning 0.024c) would do around 27M damage, enough for the shields to sit up and take notice but not quite let damage through. And a 2-hp object (a 1/64 lb or 7.1g rock) would only have to be going half that speed, and so on. 2.4%c... isn't really all that much; the speedster itself can accelerate itself up to that intrinsic velocity in only 38 minutes. It looks like the safe zone around a body with ridiculously-high gravity may be more a matter of how fast the local rubble might have been accelerated to, rather than strictly due to the dangers of the body itself. After all, I seem to recall that the fastest-spinning known neutron star twirls at 0.24c, so any tiny bits that get flung off for whatever reason (such as a random rock dropping down onto its surface and disturbing its equilibrium) are going to be moving at quite a clip...
You're off by a factor of 100 for all your damages. Collisions are Move*HP/100, not just Move*HP.

02-16-2020, 01:30 PM   #30
DataPacRat

Join Date: Nov 2004
Re: Any GURPS stats for black holes, pulsars, etc?

Quote:
 Originally Posted by awesomenessofme1 You're off by a factor of 100 for all your damages. Collisions are Move*HP/100, not just Move*HP.
<embarrassment>

... Of course, I'm going to be an annoying physics fan and complicate it up a bit, because relativity is fun. I think I'll take a reasonably high, not-particularly-relativistic speed, like 0.6c, as a baseline for damage (that is, ObjectHP * 1,962,000d), and for higher speeds, use the ratios of the Lorentz factors instead of straight speeds. That is, 0.6c has a Lorentz factor of 1.250; so an object travelling at a speed of Lorentz 2.5 would do double the damage - that's around 0.915c; a Lorentz of 10 (0.995c) eight times; a Lorentz of 100 (0.99995c) eighty times, and so on. (Or, to make it one step simpler, set damage as ObjectHP*LorentzFactor*1,569,600d.)

Now, since we're dealing with a Wall Shield of DR 30,000,000 (which I'm assuming can deflect relativistic-level masses as well as it can gamma rays), and assuming an average damage roll, then a 1-hp object (a 1/512 lb or 0.9 gram homogeneous rock) going at Lorentz 5 (0.98c) would do around 27M damage, enough for the shields to sit up and take notice but not quite let damage through. And a 2-hp object (a 1/64 lb or 7.1g rock) would only have to be going half that Lorentz (L2.5, 0.92c) speed, and so on.
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DataPacRat
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 Tags astronomy, gurps 3e, lensman, space

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