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Old 02-23-2020, 04:23 PM   #11
Pectus Solentis
 
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Default Re: Coolant [Spaceships]

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Originally Posted by Ulzgoroth View Post
If you really want your reactionless drives to have limited delta-V, I'd question why you're using reactionless drives at all.
I thought the same thing when I read this articles too.
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Old 02-23-2020, 04:28 PM   #12
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Default Re: Coolant [Spaceships]

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For some fun reading look up the "Rods from God" weapons platform. The basic idea of "Rods from God" is to put some telephone pole sized tungsten rods in orbit and then drop them on targets on the ground. Because of their size, shape, and composition they barely decelerate coming into the atmosphere and they hit with the equivalent force of a small nuclear weapon without any of the fallout.
There was a more modest plan in Project Thor to use rods that were only about the size of a crowbar, and to equip each of them with a bit of terminal guidance and a simple target-seeking system, so that each one could utterly destroy a tank or inflict a heavy hit on a battleship. That came to nothing because no sort of terminal guidance seemed to be practical on examination, and because no simple guidance system could work through the sheath of plasma that these things would make around themselves, and because tanks and ships can move rather a long way in the 22-minute minimum time from de-orbiting burn to impact.

But when you're talking about mass destruction…. A city is a big enough target not to need terminal guidance to hit it. And it moves in a slow and predictable way that means you don't need sensors to find it. A packet of orbital crowbars or a big long rod from God is going to have an atrocious effect even at "only" 7.8 km/s.

That's only 0.000 026 times the speed of light. You don't need relativistic or even 0.001 c impactors to blow a large city off the map. Any thousand-tonne spaceship in or capable of reaching low orbit is a potential seven-kiloton bomb.
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Old 02-23-2020, 04:42 PM   #13
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Default Re: Coolant [Spaceships]

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Originally Posted by ericbsmith View Post
For some fun reading look up the "Rods from God" weapons platform. The basic idea of "Rods from God" is to put some telephone pole sized tungsten rods in orbit and then drop them on targets on the ground. Because of their size, shape, and composition they barely decelerate coming into the atmosphere and they hit with the equivalent force of a small nuclear weapon without any of the fallout.
I'm familiar with them, and they have issues that their fans tend to overlook. The first being that you can't just 'drop' them and de-orbiting them in a useful time and a useful impact vector actually takes a fair bit of delta-vee. If nothing else this makes the de-orbiter relatively large, and the de-orbit burn obvious.
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Old 02-23-2020, 04:45 PM   #14
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Default Re: Coolant [Spaceships]

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Tungsten heats up too quickly for that to be effective
I'm presuming they use Tungsten because it has 3x the density of Iron. This allows it to have a smaller cross section and carry more kinetic energy to the ground. I presume they would have some sort of protective coating, and maybe an ablative end cap for reentry; that combined with the long thin reentry profile, the idea is to not have them slow down too much in the atmosphere and thus not heat up enough to melt.
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Old 02-23-2020, 05:40 PM   #15
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Default Re: Coolant [Spaceships]

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I'm presuming they use Tungsten because it has 3x the density of Iron. This allows it to have a smaller cross section and carry more kinetic energy to the ground. I presume they would have some sort of protective coating, and maybe an ablative end cap for reentry; that combined with the long thin reentry profile, the idea is to not have them slow down too much in the atmosphere and thus not heat up enough to melt.
Tungsten also has a very high tensile strength and the highest melting point of any metal, and the lowest vapour pressure at high temperatures. It has a lower specific heat capacity than iron but melts 1838 K hotter with four times the specific heat of fusion. It is tough, cohesive, and more refractory than anything else but graphite. Tungsten is strong enough to withstand a very high ram pressure, dense enough to pack a hell of a lot of momentum behind a given ram force, and better than anything else except for graphite for withstanding high temperature.

But anyway, the impracticality of Project Thor is admitted but not important, and spaceships are unlikely to be built out of tungsten. The point was that any spaceship in or capable of reaching low orbit is weapons-grade. It's the very least and most inescapable demonstration of Jon's Law: "any interesting space drive is a weapon of mass destruction".
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Old 02-23-2020, 05:59 PM   #16
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Default Re: Coolant [Spaceships]

Replacing reaction mass with something else that gets used up (typically some sort of energy-producing fuel, but coolant could be an option) can be interesting from a background standpoint, but typically doesn't have a lot of impact on how ships function in the setting (aside from letting you ignore the issue of dangerous exhaust). Coolant can be a particularly interesting variant, because one can (presumably) use it a few different ways. A vessel with resupply readily available nearby can keep itself comfortably cool by venting coolant (probably using heat pumps to shunt heat into a small portion of it, boiling it, then releasing the steam). One that needs to be more conservative is going to tend to get rather warm during engagements and the like, as the coolant keeping the thrusters, power plants, and weapons from melting has no choice but to evenly distribute all that heat throughout the ship, radiating what little heat it can into the vacuum of space passively. In a crisis situation, the captain may have to make the difficult choice between venting coolant to keep important components (like the crew) from overheating or having enough available to be able to get back home in a reliable timeframe (or just have enough to get through the next battle). It may also influence tactics and decision-making from the other side ("Captain, their ship appears to be out of coolant. If we keep pursuing them, they're going to have a complete meltdown of their thrusters; the resulting antimatter explosion will almost certainly kill their hostages.").

What replacing reaction mass with coolant doesn't get you, however, is a useful spaceship that cannot be used as a WMD. For that, you've more-or-less got to break physics - teleportation, pseudovelocity, hyperspace travel, etc. Heck, even those still get you WMD's in the form of orbital drops, so you've got to combine them with the sort of social structures that prevent that.
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Old 02-23-2020, 06:05 PM   #17
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Default Re: Coolant [Spaceships]

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Tungsten heats up too quickly for that to be effective (it needs only .11 J/K/g, meaning that its higher melting temperature only matters if it does not keep heating up). Iron, by comparison, takes four times as much energy to heat up, and has a decent melting temperature and a decent density.
Heating from re-entry is not as serious an issue (for OKE weapons) as you seem to think. When a meteorite strikes the ground it is, typically, still icy cold inside, the incandescence being superficial, and time for conduction of heat from the surface to the interior rather short.

You may be thinking of the heat shielding that is required for spacecraft that rely on aerobraking to shed significant speed. Remember that those are designed and put on trajectories that maximise the transfer of energy and momentum to the air, whereas an orbital-kinetic-energy weapon would be designed and deployed to minimise friction, not maximise it.
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Old 02-23-2020, 08:57 PM   #18
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Default Re: Coolant [Spaceships]

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Originally Posted by Agemegos View Post

But anyway, the impracticality of Project Thor is admitted but not important, and spaceships are unlikely to be built out of tungsten. The point was that any spaceship in or capable of reaching low orbit is weapons-grade. It's the very least and most inescapable demonstration of Jon's Law: "any interesting space drive is a weapon of mass destruction".
Jon's Law seems to make it almost axiomatic that a successful space-faring civilization is going to have to have far better social and political control mechanisms than we current have. Even playing around in Kerbal Space Program, I've seen the problems of just how destructive a powerful rocket can be while doing routine things, such as rendezvous and docking. Kerbal lets me avoid a lot of the repercussion of mistakes through saves and reloads, as well as mechanical limits that keep impacts from cascading, but in reality, those are not mechanisms that apply.


I still haven't wrapped my head around it completely, but it seems like there is almost a need for a rather strict protocol for spaceship ownership and operation.
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Old 02-23-2020, 09:25 PM   #19
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Default Re: Coolant [Spaceships]

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Jon's Law seems to make it almost axiomatic that a successful space-faring civilization is going to have to have far better social and political control mechanisms than we current have.
Yeah. The way I went with the setting I devised for interstellar SF was to have an absolutely monopoly on starships and strict licensing and control of spaceships*. Another possibility is to have all spaceships controlled by rigidly programmed non-sapient AI computers with highly effective precautions against their being deactivated, over-ridden, or sabotaged.

It you go that way you have to think carefully about what (if anything) you were getting out of letting PC types have ownership or control of spaceships, and how to retain that. Of course one of the possibilities is to ignore Jon's law as a genre convention, to agree that the WMD potential of spaceships will simply not be used or mentioned, to preserve the jolly Star Wars or Traveller vibe. If you're doing that, then in my opinion the best thing is to offer only a simple rationalisation or none. Detail draws attention (especially the attention of SF fans), and you want players thinking about something else.
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* The SF RPG I used for that setting, ForeSight, had some grumbling at the beginning of the spaceship design and construction rules along the lines of "What would an SF RPG be without spaceship design and construction rules? I wanted to help you find out, but…". The chapter ended with something like "There you go, then. Yes, they are expensive, aren't they? Fly Galactic, and avoid used-spaceship dealers."
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Old 02-23-2020, 09:29 PM   #20
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Default Re: Coolant [Spaceships]

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Originally Posted by Verjigorm View Post
Jon's Law seems to make it almost axiomatic that a successful space-faring civilization is going to have to have far better social and political control mechanisms than we current have. Even playing around in Kerbal Space Program, I've seen the problems of just how destructive a powerful rocket can be while doing routine things, such as rendezvous and docking. Kerbal lets me avoid a lot of the repercussion of mistakes through saves and reloads, as well as mechanical limits that keep impacts from cascading, but in reality, those are not mechanisms that apply.


I still haven't wrapped my head around it completely, but it seems like there is almost a need for a rather strict protocol for spaceship ownership and operation.
I wouldn't say you need to be all that exotic. Pretty much apply air traffic control rules, but with system-wide control rather than only exerting control over relatively small envelopes around key areas.
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