Coolant [Spaceships]

[AlexanderHowl]

Because superscience reaction drives that have high thrust and high delta-v are also WMDs in disguise. For example, a TL9^ nuclear saltwater reactor is continuous nuclear detonation that sprays radiative death as its reaction mass and it is the least dangerous of the bunch. A SM+6 shuttle with a TL12^ total conversion drive converts 3g of matter into pure energy per second, effectively detonating a 60 kiloton fusion bomb beneath it every second.

Coolant avoids both forms of WMD while allowing for a pleasing delta-v. A spacecraft with one component of water could achieve a delta-v of 500 mps while a spacecraft with ten components of water could achieve a delta-v of 7,000 mps. Of course, there may be some abuse still, so changing the duration of coolant to one hour per 1g of acceleration may be better (it still gives 20 mps and 280 mps respectively). At that point, spacecraft can get up to an acceptable delta-v without worrying about WMDs.

[Rupert]

Originally Posted by AlexanderHowl

Coolant avoids both forms of WMD while allowing for a pleasing delta-v. A spacecraft with one component of water could achieve a delta-v of 500 mps while a spacecraft with ten components of water could achieve a delta-v of 7,000 mps. Of course, there may be some abuse still, so changing the duration of coolant to one hour per 1g of acceleration may be better (it still gives 20 mps and 280 mps respectively). At that point, spacecraft can get up to an acceptable delta-v without worrying about WMDs.

You do realise that at ~3 km/s (~2 miles/second) an object has kinetic energy equal to the chemical energy a lump of TNT of the same mass releases? That means that at 20 mps a 100 ton shuttle impacts with about 10 kilotons of energy. Any spaceship that can traverse interplanetary space at a half-reasonable speed and which is of a decent mass is a WMD, if it follows physical laws as we understand them.

If I was designing a setting from scratch that had fast space travel I'd consider wormholes or other FTL jumps that started in planetary orbit, so spaceships wouldn't need vast delta-vee to travel quickly, and/or inertialess drives that don't retain pre-engagement vectors (though they have other issues, I'm sure), and just throw out hard physics.

[Agemegos]

Originally Posted by Rupert

Any spaceship that can traverse interplanetary space at a half-reasonable speed and which is of a decent mass is a WMD, if it follows physical laws as we understand them.

It only needs to be in orbit, or capable of reaching orbit.

[ericbsmith]

Originally Posted by Rupert

Any spaceship that can traverse interplanetary space at a half-reasonable speed and which is of a decent mass is a WMD, if it follows physical laws as we understand them.

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.

[AlexanderHowl]

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. A 10 meter long by 1 meter wide rod with a 10 meter long conical cap would mass around 80 meter and would hit with 800 metric tons of force (a third less than a similar tungsten rods). In addition, iron is everywhere on the moon, so you can just make spikes by the millions and use mass drivers to launch them from the moon.

[ericbsmith]

Originally Posted by AlexanderHowl

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.

[Agemegos]

Originally Posted by ericbsmith

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".

[Verjigorm]

Originally Posted by Agemegos

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.

[Varyon]

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.

[Agemegos]

Originally Posted by AlexanderHowl

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.