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Old 03-02-2020, 10:27 AM   #111
Fred Brackin
 
Join Date: Aug 2007
Default Re: Coolant [Spaceships]

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Originally Posted by Varyon View Post
I wonder if the remnants would indeed impact the target, considering the target is in motion. An obstacle that is struck by an RKK is going to generate a large explosion, which is going to impart thrust onto the RKK. Said thrust will be only for a moment, but will be of sufficient force to turn the RKK into rubble. t.

Separate atoms rather thna rubble. The molecular binding energies of what look like very solid objects to us are rounding errors when compared to the KE of relativistic objects.

Then of course, kinetic interceptors do the same sort of damage to relativistic objects that those objects would do to their targets. The only difference is that of mass.

So when virtually any sort of projectile hits your "RKK" there will e a burst of hard X-rays sufficient to ionize the entire mass of the the RKK. It will then become a rapidly expanding cloud of ions and though it may techically "hit" it's original target it does so one atom at a time and many of those atoms may miss entirely.

Everyone should stop thinking about these "solid object" things. They (and the rules that bind them) don't exist in collisions above a few miles per second.
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Old 03-02-2020, 11:32 AM   #112
AlexanderHowl
 
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Default Re: Coolant [Spaceships]

Very true. Of course, the hard gamma and cosmic rays produced by relativistic collisions will likely cause massive radiation damage to anything in orbit.
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Old 03-02-2020, 11:37 AM   #113
Fred Brackin
 
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Default Re: Coolant [Spaceships]

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Very true. Of course, the hard gamma and cosmic rays produced by relativistic collisions will likely cause massive radiation damage to anything in orbit.
Even if the thing does flash into ions in the upper atmosphere you might be able to sterilize a continent. It's those precion citybusters that are in the wrong queue.
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Old 03-02-2020, 02:52 PM   #114
AlexanderHowl
 
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Default Re: Coolant [Spaceships]

That would depend largely on the size of the spacecraft, the speed of the spacecraft, and the distance from the surface. A 1,000 metric ton spacecraft traveling .1c would have ~100 gigatons worth of energy. At 10,000 km, the energy would likely be 358 kJ per square meter or 35.8 J per square centimeter, so it would wreck unshielded objects and increase the radiation belts, but it would not sterilize a continent. A 1 million metric ton spacecraft going .5c that detonated 1,000 km away would release 89.5 MJ per square centimeter, which would vaporize a continent (and probably sterilize the planet).
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Old 03-02-2020, 03:51 PM   #115
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Default Re: Coolant [Spaceships]

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Originally Posted by Fred Brackin View Post
Even if the thing does flash into ions in the upper atmosphere you might be able to sterilize a continent. It's those precion citybusters that are in the wrong queue.
For an object manufactured with a bit of brains and precision engineering, it's totally possible. What you do is, rather than using a single impactor, you use a series of objects striking the same location to drill a path through the atmosphere (and the ground, if you want). Precision isn't going to be great, but it can get away with no more wide area devastation than you'd get from nuclear weapons.
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Old 03-02-2020, 11:43 PM   #116
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Default Re: Coolant [Spaceships]

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Originally Posted by Fred Brackin View Post
You need an asteroid 7 miles across at .99 c to turn an Earth-like planet into an asteroid belt. It'd be a lot of trouble to go to and nobody is likely to ahve amotive to do it. They probably don't even have motive to do that asteroid at the much more modest 15 miles per second of Earth's dinosaur killer.

Hyperbole even if only used for effect doesn't help these arguments.
It's not entirely hyberbole, unfortunately. Yes, it's pointless to do such a thing, extravagant and silly...but a 'classic' reactionless drive makes it potentially possible to do it, and where such a possibility exists, there's a breed of player who'll grin like Calvin from the old comic strip when he recognizes this, and pretty soon he's trying it because it's So Cool.
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Old 03-02-2020, 11:46 PM   #117
Johnny1A.2
 
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Default Re: Coolant [Spaceships]

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Originally Posted by Agemegos View Post
Earth's gravitational binding energy is approximately 2.24 × 10³² J.

An asteroid 7 miles across would have a radius of 4.8 × 10³ m and a density of maybe 2 200 kg/m³, for a total mass of 1.0 × 10¹⁵ kg. The relativistic expression for kinetic energy is E = mc² {[1 / √(1- v²/c²)] - 1}. Substituting v = 0.99 c we get E = 6.09 mc², and that works out to 5.48 × 10³².

That's close enough for government work: Fred might have been assuming an ice asteroid instead of an asteroid composed like Ceres.



Some people have very horrible motives. We've had people bring together a great many resources in an attempt to cruelly murder the entire Jewish race, and several other organised mass murders with death counts in millions. And we've had people murder three thousand innocent civilians in an attempt to start a war that would end the world. There really are people who try to imminentise the eschaton.

I think it's better to focus on the idea that its probably very difficult to fit a reactionless drive to anything vast enough to actually destroy the Earth. The destruction of Earth as an object is hyperbole.

The devastation of a large city is not.
It also opens up other possibilities that the GM might not want to deal with. For ex, if you can travel at significant percentages of c, you can attack space-going structures and ships simply by launching streams of dust at them. It's possible to think of potential countermeasures against ships and big rocks, but stopping a stream of fine mist moving at you at .2c is another matter.

Also, a GM might prefer to avoid time dilation issues. A 'classic' reactionless drive opens up serious time dilation possibilities.
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Old 03-03-2020, 05:46 AM   #118
AlexanderHowl
 
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Default Re: Coolant [Spaceships]

Yes, time dilation is always an issue when traveling at high velocities. If you want to have some fun though, try time compression for your FTL drives (though you need to throw an absolute in the formula to avoid 'i'). It ends up that time compression roughly equals velocity in 'c' (a spaceship going 1000c roughly experiences 1000x the time as the outside Universe). Total automation and nanostasis are required for any trip (at 1000c, a trip to Alpha Centauri will take less than two days in the outside Universe but will take around 4.37 years within the spaceship).

Imagine the tactical applications though. A spaceship jumps a light-month after a battle. While less than an hour passes in the outside Universe, the crew of the spaceship has an effective month to perform repairs. Of course, that would mean that reactors would need to be refueled quite often.
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Old 03-03-2020, 09:59 AM   #119
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Default Re: Coolant [Spaceships]

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Originally Posted by AlexanderHowl View Post
Yes, time dilation is always an issue when traveling at high velocities. If you want to have some fun though, try time compression for your FTL drives (though you need to throw an absolute in the formula to avoid 'i'). It ends up that time compression roughly equals velocity in 'c' (a spaceship going 1000c roughly experiences 1000x the time as the outside Universe). Total automation and nanostasis are required for any trip (at 1000c, a trip to Alpha Centauri will take less than two days in the outside Universe but will take around 4.37 years within the spaceship).
As velocity approaches c, time dilation expands toward infinity (which, I think, means photons don't experience time?).

You can make up whatever math you want regarding passage of time in FTL, but its just that: made up. I think most of the serious suppositions (like the Alcubierre drive) assume a false movement that creates a sort of space-time moving sidewalk, and create a state where no actual FTL travel occurs. Still breaks causality, though.
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Old 03-03-2020, 11:29 AM   #120
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Default Re: Coolant [Spaceships]

Well, that depends on whether certain formulas are actually complete. Since the break in causality is represented by negatives or square roots of negatives occuring in the formulas, it may just be that the formulas are incomplete (lacking absolute functions). Unfortunately, this is quite difficult to test, as we will not know if formulas are incomplete unless someone actually stumbles upon FTL and, since everyone would 'know' that FTL is impossible due to the incomplete formulas, it is highly unlikely that any would receive sufficient funding to do the necessary research anyway.
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