Coolant [Spaceships]

[Rupert]

Originally Posted by Johnny1A.2

An unmodified reactionless drive (that is, the classic by-your-bootstraps) has the opposite problem, it's too good (aside from violating conservation of momentum). Before long, some bright PC will get a funny look on his face and the next think you know people are throwing R-bombs at each other, and converting planets into asteroid belts.

They will also have perpetual motion engines that produce truly ridiculous amounts of power, and probably half a dozen other things before breakfast.

[Fred Brackin]

Originally Posted by Johnny1A.2

Th the next think you know people are throwing R-bombs at each other, and converting planets into asteroid belts.

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.

[whswhs]

Originally Posted by Agemegos

There is an explanation somewhere of the difference between SF and sci-fi that goes like this: "The hero asks the Professor how her time-machine works. In SF you get a page and a half about relativity, quantum mechanics, and the Garden of the Forking Paths. In sci-fi the Professor says "Sit in this seat here, shut the door, turn the power switch to 'on'. Then set the target date on this dial here, and push the big yellow button."

Long ago, I interviewed Tim Powers when he was Guest of Honor at a science fiction convention. At one point, he talked about The Stress of Her Regard, which had silicon-based lifeforms. What he said was that he had discussed this with Gregory Benford, and Benford had said two things: first, that silicon-based lifeforms and intelligences weren't physically plausible; second, that if he wanted to use them anyway, here was the handwaving he had to do to get the readers to accept them. . . .

[whswhs]

Originally Posted by Johnny1A.2

An unmodified reactionless drive (that is, the classic by-your-bootstraps) has the opposite problem, it's too good (aside from violating conservation of momentum). Before long, some bright PC will get a funny look on his face and the next think you know people are throwing R-bombs at each other, and converting planets into asteroid belts.

It seems to me that if you have a reactionless drive, then it violates conservation of momentum, by definition. So why not just say that conservation of momentum is also violated when it "collides" with a planet? Reactionless ships never crash; they just stop dead.

[Fred Brackin]

Originally Posted by whswhs

It seems to me that if you have a reactionless drive, then it violates conservation of momentum, by definition.

That generally gets plowed under by the way typical reactionless drives violate conservation of energy. A drive that used fuel the way a 100% efficient total conversion drive did wouldn't but the typical drives far exceed those numbers.

For example and using Spaceships numbers a ship with such a drive that was 50% fuel tank would run dry in a little over 38 weeks (though it is nearing c). Compare that to Anthony's numbers of the 250 MW reactor running all year on 2 kg.

A ship that used no reaction mass but didn't violate conservation of energy might be not really much more interesting to adventure writers than a hard scicne one that did use reaction mass.

[Polkageist]

I think having caveats on reactionless drives is kinda nice because it gives flavor to how they work and dress up some of the setting to be more than just spheres eerily pushing themselves through space.

Like, I've thought of the whole "why do reactionless drives need/have clear thruster-like modules on all these artworks?" and the justification that I came up with in my mind is that while the drives are reactionless, they are directional (in that they create a "thrust") and that they radiate a waste or something similar that is better off ejected out the back of the ship, even if it's just waste heat. Voila, now you have nice glowy engines.

Just thinking about coolant as a limiting factor is interesting as well and is a neat justification for having variable thrust reactionless drives and a cost/benefit tradeoff for higher accelerations. After all, if a drive has a thrust of say 1g then there's little reason not to run it at max cruising thrust all the time. Giving players choices is fun though!

Consider a classic GURPS reactionless drive that can cruise at 0.1g by default. Under the hood as it were, this is enabled by a coolant cycle that keeps the engine operating at equilibrium. Dump heat via radiators or whatever. No need to take anything special into consideration, go at 0.1g in a direction. Say the players want to go faster?
Ok! Bump up that acceleration to 0.5g and now your endurance before you have to stop and cool off is, say... I dunno, 24 hours. Crank it up to a full 1g of acceleration and you've got 12 hours before it hits that shutdown threshold. Savvy engineers can monkey with this equation to get more out of the engine, push that red line farther, and maybe get an edge on the cooling efficiency from a stock system.

At the very simplest, you just need to inform the players that they can cruise at 0.1 for as long as they want, and go faster for limited sprints.

A little more complex, the engine can cool off 10 units of heat/hour and produces 10 units of heat per 0.1g of acceleration. The ship's heat sinks can handle up to 100 heat units before they're topped up and have to cool.

I'll admit that nothing stops this from being a WMD, but on top of the problem of any fairly heavy object moving at speed being capable of varying degress of destruction, WMDs themselves have something of a mental block to being used by all but the exceptionally psychopathic villains. On that point, having the players working to STOP an exceptionally villainous villain from doing such a thing is an excellent story beat.

Kind of like other exhibitions of wanton villainy, a player that posits using a fast-moving spaceship to smash a (typical inhabited) planet would probably call for a pause of the game and a sidebar about what's going on man. Especially if that's the response to some non-existential problem. It's a hell of an escalation! It's like getting some McDonald's, the fry order is wrong, and concluding that the appropriate response is to set fire to the restaurant.

[Agemegos]

Originally Posted by Fred Brackin

You need an asteroid 7 miles across at .99 c to turn an Earth-like planet into an asteroid belt.

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.

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.

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.

[Agemegos]

Originally Posted by Polkageist

Kind of like other exhibitions of wanton villainy, a player that posits using a fast-moving spaceship to smash a (typical inhabited) planet would probably call for a pause of the game and a sidebar about what's going on man. Especially if that's the response to some non-existential problem. It's a hell of an escalation! It's like getting some McDonald's, the fry order is wrong, and concluding that the appropriate response is to set fire to the restaurant.

It isn't just an issue in play of a player character doing this in peace-time. It's also a setting-design issue that reactionless drives — or any Jon's-Law-compliant spaceships — are available to belligerents, guerrillas, terrorists, and omnicidal fanatics. The setting ought to show the scars of previous use or the apprehension of imminent use.

[whswhs]

Originally Posted by Agemegos

It isn't just an issue in play of a player character doing this in peace-time. It's also a setting-design issue that reactionless drives — or any Jon's-Law-compliant spaceships — are available to belligerents, guerrillas, terrorists, and omnicidal fanatics. The setting ought to show the scars of previous use or the apprehension of imminent use.

I'm remembering the young woman who applied to join the Legion of Super-Heroes back when I was following it. Her introduction ran, "My scientist father gave me the ability to make the sun become a supernova. I can do it once."

[Polkageist]

I suppose when it really comes down to it, it's probably best dealt with by labeling it "Atrocity-not-appearing-in-this-game".

Or, reserved for the really evil villain's villainous plot that the players stop. Why hasn't anyone done it before? Because it's an act so heinously vile that no one seriously considers it. Until this baddie. That you're going to stop, heroes. Get to it.