Coolant [Spaceships]
 

One of the primary issues with reactionless engines is that they allow for every shuttle to become a WMD, as a SM+6 shuttle traveling at .01c is the equivalent of 100 megaton bomb. One way to deal with this issue is to arbitrarily have a speed limit, which mechanically works but is unsatisfying. Another way to deal with it is to use a consumable to limit the duration of the thrust, either as fuel or as coolant.

I tend to favor coolant because you can use water. For example, a reactionless drive could transform one component of water into steam (which is vented) for every days of thrust × acceleration (a spaceship with 4g acceleration would vent four components of coolant every day). Since the thrust required for sustained acceleration would decrease as mass decreased, coolant would effectively function like reaction mass (for example, 10 components of coolant would allow for 14 days of thrust at 1g). When a spacecraft runs out of coolant, it suffers 10% of HP for every combat turn that it continues to maintain thrust, as the waste heat causes massive damage to the drives.

So, would you use coolant to control reactionless drives? Have you used something similar in your games? If so, what was your experience like?

Re: Coolant [Spaceships]
 

Seems like a solution in search of a problem to be honest. Just incorporate some kind of practical lock against high-speed ramming or just say out of universe "No, that's not a thing that fits into the game I'm trying to make."

Re: Coolant [Spaceships]
 

If you really want your reactionless drives to have limited delta-V, I'd question why you're using reactionless drives at all.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

Really. At that point just take one of the superscience Fusion Torches and adjust the thrust and/or fuel usage to suit your needs.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

Torch scorch isn't much of a disguise, and is relatively easy to weaken as a weapon.

Imposing low reaction-stream focus on superscience torches stops them working as long range beam weapons. And at short range that "60 kiloton fusion bomb beneath it every second" isn't actually much like a 60 kiloton bomb - it doesn't stack up the energy into one big pulse, and in an atmosphere the engine is probably destroyed in much less than a second of operation.

There is the threat of holding a vacuum habitat hostage at docking ranges, though.

(NSW, on the other hand, is ludicrously unsafe at a minimum because it's a continuously-operating dirty bomb that makes Project Pluto look environmentally responsible. When operated as intended! And can be easily or accidentally converted into a nuclear meltdown instead.)
Coolant doesn't avoid arbitrary-velocity kinetic strikes, it just means you need to put in a little effort - you could retain the hot coolant and chill it down with radiators instead of discarding it. That would presumably hit your sustained acceleration pretty hard, but it's really hard to rule that people can't cool hot water.

(Plus that 7000 mps from 10 systems is nearly 0.04c, so if you're considering 0.01 c to be too much kinetic energy to allow, you've failed to produce the desired constraint by more than a factor of 3.)

Re: Coolant [Spaceships]
 

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

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

I thought the same thing when I read this articles too.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

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".

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.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

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.
___________

* 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."

Re: Coolant [Spaceships]
 

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.

Re: Coolant [Spaceships]
 

Enforcement will need to be truly draconian, immediate (and if you have an accident that leaves you out of control and on a collision course with something important, tough luck), and thorough.

Re: Coolant [Spaceships]
 

The problem with the Tyranny of the Rocket Equation is that sometimes you don't want anarchy, you just want a more tolerant regime. Replace the Tyrant with a more easy-going ruler.

Re: Coolant [Spaceships]
 

It'll need something. There are several different forms that something could take.

As for WMDs, a distinction needs to be made. 'WMD' covers everything from one-kiloton mininukes to R-bombs that can shatter planets.

Reasonable mass orbital and interplanetary vessels are certainly WMDs, but they tend to be WMDs on the lower end of the scale. Let's say you've got a 1000 metric ton ship moving at 100 kilometers/sec. That's a nice clip for interplanetary travel, beyond current state of the art.

It'll hit with a force of about 1 megaton, if I didn't slip a digit in my BOTEC. OK, that's certainly a WMD. It's as big as a biggish strategic nuke.

But the flipside of that is that we already have 1 megaton nukes. We've had them for over half a century. So such a ship doesn't really add anything to the picture that isn't already present, and it would be an inefficient way to deliver a 1 megaton boom compared to a nuke.

Such ships would imply very good space traffic control. There would be radar nets and other sensors tracking ships, trajectories would be filed and approved, etc. Ownership could be anything, as long as the operations are prevented from doing damage. But such vessels, which would be fully sufficient for a Solar System wide civilization, would not really change the WMD big picture much.

Where Jon's Law really starts to bite is when you start getting up into thousands of kilometers/sec, or ships with enormous masses.

Re: Coolant [Spaceships]
 

How much would it help to have rather fragile (and not "streamlined") space ships that would break up in atmospheres? And while real life shuttles are "streamlined" they are still pretty fragile if not deorbited in just the right way so you'll use similar crafts (and elevators etc) to get up and down.

Re: Coolant [Spaceships]
 

I check your BOTEC

What does make a difference is that the control problem on a nuke is a lot easier than the control problem on an airliner. You can lock your strategic weapons away in guarded armouries, and exercise extreme vetting over the officers who control them. But freighters and passenger liners have to be out and about with all sorts of people having easy access to them.

In September 2001 I was running an SF campaign in which the PCs were involved in counter-terrorism in my usual Jon's-Law-obsessed interstellar SF setting. One of my players was from New York. I had to end the campaign abruptly.

Re: Coolant [Spaceships]
 

I tried to at least alleviate the WMD problem by cribbing from Poul Anderson et al:

Drives IMTU (In My Traveller Universe)

(Three drives is because I also discussed the FTL drives.)

Re: Coolant [Spaceships]
 

My plan is to have the m-drive kill your velocity relative to any large mass 'nearby', to avoid tricks involving building up huge vectors some-place else, and then lining up the ship and turning off the m-drive (a trick you can do with 2300AD-style stutterwarps and the like, if you've the patience).

This also gets around questions about matching orbital velocities with planets and adjusting for relative stellar velocities when your main drive doesn't add real velocity.

Re: Coolant [Spaceships]
 

Some, particularly if you can ensure a shallow angle of entry. Until you get into really big bangs an iceball exploding at 114 000 feet isn't going to do a lot of damage on the ground.

Here's the Earth Impacts Effects Calculator. It's really intended for meteors and asteroid impacts, and if you model spaceships as chunks of ice they don't seem too terrifying.

However, your spaceship security has to contend not only with spaceships that are in space deciding to land without retrorockets, but also with spaceships with enough fuel and propellant to fly to Mars deciding to take off into the side of a government building instead of into space.

Re: Coolant [Spaceships]
 

We're talking about real space problems, so 'accidentally on a collision course with something important' is a negligible case. 'Deliberately on a collision course with something important but accidentally lost the ability to get off it' is a little less so, but not allowing interplanetary flight plans that have a suicide burn at the end isn't exactly a hard concept.

Also in real space factors, the distances of any trip aren't short, and the times aren't all that short as a result. You only need immediate enforcement if somebody is going to plow into something at kps on the same level of immediacy, and you should never have allowed a flight trajectory that would let them abruptly change from 'safe' to 'ramming' in anything close to your reaction times in the first place.

Any kind of enforcement of anything needs to be thorough, in proportion to the degree that you actually want to prevent it rather than occasionally using it to justify doling out punishments. You probably do genuinely want to prevent hyper-velocity kinetic strikes, so yeah. And the fact that no modes of interaction between 'talk to them' and 'destroy them' are really possible with a ship at high relative velocity, 'draconian' is the only option on the table. That said, both of these things apply to ATC as well, and they scarcely ever ask for a plane to be shot down and usually are not considered irresponsible in that practice...



There is a space where you've got pretty short time-frame problems if you have high-thrust main drives. At some point many ships want to come very close indeed to potentially delicate space habitats. If our 100-ton suicidal shuttle has 1g acceleration and suddenly burns from rest towards a hab 35 km away, it won't be going at ridiculous speeds when it gets there a minute later but 500+ m/s is probably plenty to cause some major damage.
If you don't know for sure what's inside the spaceship, there's the concern that the same people responsible for its trajectory have given it a high-density atmosphere-penetrating payload. If they're not too picky about accuracy they won't even need to release it instead of letting it find its own way out when the ship hits atmosphere.

Although with reasonable information you should be able to judge the total payload mass, you probably can't externally tell whether it's a 100 ton cargo of plastic sheets or a 100 ton tungsten cannonball.
The OP's proposal literally keeps the rocket equation in! The only thing it changes is not having a high-energy exhaust stream.

Re: Coolant [Spaceships]
 

No. I would not use coolant. My explanation for why my reactionless engines have an upper speed limit is that interacting with the dark matter that they use for virtual propellant creates drag and at at sufficiently high speed drag equals thrust.

Re: Coolant [Spaceships]
 

Found a site with worked numbers. https://space.stackexchange.com/ques...-get-you-there

These are all from earth

The Moon / Luna:
Closest to Earth (Supermoon): 356,577 km
Travel time (at 9.80665 m/s2, no deceleration): 2h 22m 12s
Travel time (at 9.80665 m/s2, decelerating halfway): 3h 20m 24s

So turnover at 1h 40m gives you 42m to stop it. Should be doable if it isn't a warship with armor and point defenses.

Mars:
Closest to Earth: 65 million km
Travel time (at 9.80665 m/s2, no deceleration): 1d 7h 58m 5s
Travel time (at 9.80665 m/s2, decelerating halfway): 1d 21h 13m 1s
Turnover at 23h, gives about 9 h to stop it.

That all sounds like you can with procedures and pre planned interceptors deal with it.

Lots of possibility for complacency, budget cutting and such to make it a PC problem that they have to make do.

Re: Coolant [Spaceships]
 

What about the case where the rogue ship doesnt degenerate?

Re: Coolant [Spaceships]
 

Thing is, you can't 'stop' it - you have to either deflect it or blow it into bits too small to harm whatever they're going to hit. This what what I mean about 'draconian penalties', and 'being thorough' - you need to make the call and then act swiftly, and the correct action is to blow the ship and everyone in it into teeny tiny pieces.

Re: Coolant [Spaceships]
 

That's an important part of the rocket equation, and especially the rocket equation's tyranny. The tyranny comes from the fact that both momentum and energy are conserved, but energy increases with the square of velocity, while momentum increases linearly.

the coolant drops the energy part of the equation. Its odd, but I can see settings where it is the right option.

Re: Coolant [Spaceships]
 

Earth moves a lot in the ~58 minutes between the two scenarios, meaning you'd need to have a different trajectory between the two. When the computers plug your trajectory into the appropriate calculations, they're going to spit out that the only way you can reach Earth is if you do so at a rather unsafe speed - in other words, they will detect that you're using your vessel as a weapon roughly as soon as you launch. If you start with a "safe" trajectory, you'll have to use extra time (and delta-v) to put yourself onto a hostile trajectory in order to impact the target, and they'll detect the problem as soon as you start to deviate from the safe trajectory. So, they'll have a lot of time to stop you. If they can stop you before you complete your acceleration, whatever "stop" method they use will mean you miss your target entirely (your remains will be moving too slowly to intercept). If you've completed your acceleration, simply blowing you up will still leave the target to deal with your expanding debris cloud; even a planet with sufficient atmosphere to tank said cloud would have the problem of having satellites get destroyed (which could result in a cascade). With enough time before impact, they can probably nudge you off course (then destroy you if you have the means of getting back on course) using lasers or the like to make certain you miss the target entirely.

"You need to find a way to stop the attack before the authorities do, or their methods are going to vaporize the (VIP/MacGuffin/PC's) on board" can also work.

Re: Coolant [Spaceships]
 

...I don't know what you think the "tyranny of the rocket equation" is, but I reiterate that the consumable coolant literally results in the rocket equation being followed and the OP explicitly observed that fact.

The reactionless+coolant causes conservation laws to be breached, certainly, but doesn't actually give the ships different performance from a rocket. (Potentially a very good rocket, but nonetheless.)

Also, kinetic energy increasing as the square of velocity doesn't actually pose any problem for rockets, just for people getting confused looking at them. You can derive the rocket equation without making any reference to conservation of energy.

Re: Coolant [Spaceships]
 

In general, if you're using reactionless drives, you're throwing realism out the window, and they also don't actually do a great job of emulating most fictional genres (there are edge cases like The Forever War), so I find it simplest to just remove reactionless drives, and replace with techs that do a better job. The usual candidates are:

• Ether Drive: the drive works by pushing on the ether, or something similar. This means it has airplane-like performance -- deceleration and turning are relatively easy, but acceleration drops sharply as velocity increases (power requirements are equal to the dot product of force and velocity). Obviously this is throwing relativity out the window.
• Planetary Drive: similar to an ether drive, but instead of pushing on the ether, it pushes on nearby large masses. This adds an additional limit on acceleration, as it is also reduced if there are no nearby large masses (a reasonable cap is some multiple of local gravity).
• Sublight Warp Drive: it's just the setting's FTL drive, tuned down to be slower than light. There are reasonable energy arguments for FTL drives having a max speed that is inversely proportional to local gravity. This has the useful side benefit that speed is much lower in the areas that are most interesting to be in -- a drive that can get anywhere on Earth in an hour can get just about anywhere in the solar system in eight hours (oddly, Mercury is the hardest to get to).

Re: Coolant [Spaceships]
 

The simplest way to prevent a fast ship from being a WMD is to remove it's kinetic energy entirely. Pull out the psuedo-velocity design switch. This allows you to get from place to place without long periods of down time, but you can't wind a ship up to relativistic speed and wipe out cities.

In my own in-development setting, I'm toying with the idea that the superscience behind reactionless drives is very sensitive to relativistic effects, and their performance drops off drastically as speed increases, before just not working at all at some point. I haven't put anything down on paper (divide by some power of the Lorentz factor, mayhaps?) yet.

But, as people have pointed out, there's no real way around the fact that something SM +6 or bigger at orbital velocity is already carrying enough energy to do some real damage.

Re: Coolant [Spaceships]
 

It's understandable but linguistically funny to talk about being "sensitive to relativistic effects" in a way that is clearly discarding the lack of a privileged reference frame that is the nominal bedrock of relativity.

Re: Coolant [Spaceships]
 

Umm. Speed in what frame of reference? If you are about to discard the Principle of Relativity, it's best not to draw attention to the Theory of Relativity right at the point where you do it.

My earnest advice is that an inertialess, reactionless, pseudovelocity, or FTL drive cannot be made convincing, and the more you try the more you draw attention to the exact spot that you want players to look away from. Get over heavy ground as light as you can. Tell players the operational characteristic of your superscience as briefly and baldly as possible, flush the pseudoscientific rationalisation, and pass quickly to some other point of interest, such as technoninjas, pirate catgirls, and the Neo-Confucian Space Empire. Players don't worry about physics problems while their techo-youxia are flirting with the guards on the air-gangway of a pirate-catgirl space-cruiser.

Re: Coolant [Spaceships]
 

I'm sold on the catgirls! Pirate or not. Who cares how it flies, as long as we fly with them ?

Re: Coolant [Spaceships]
 

My take as well.

The thing that WMD spaceships actually points at is a way more fundamental problem than your ships can kill cities. It is that a space drive that can kill cities is also a power plant comparable to the generating capacity of some nations. A culture so rich people so downscale they are willing to live as adventurers have access to private generators that could power Belgium is so alien to our experience it's tough to tell meaningful stories about it at all. You are *already* ignoring so many other utterly transformative effects of vast amounts of energy being available that ignoring one more (you can use it to build really big bombs....) is basically trivial. It apparently is the one people see it is being ignored most easily, but those others are still there in "reality", it's just nobody is pointing them out.

Re: Coolant [Spaceships]
 

I found an interesting thing called Bell's spaceship paradox...which I plan to wave around the same area as "the reactionless drive is enabled by hitherto unknown subatomic forces found in meta-stable alloys of super-heavy post transuranic elements." The ability of these materials to affect space-time in a way that violates classical and relativistic physics is due to relativity rearing its head at an atomic and sub-atomic level. As for what inertial frame...it could be relative to the frame of the location where the PTU alloy was manufactured...or to some unknown "ground state" of space-time. Other superscience in this setting is a hyper drive that works by shifting mass into the bulk from the current brane, so a "ground state" may make be useful for describing that.

It's superscience...it's all about how creative you can get with the technobabble. FWIW, I do run some of these by a PhD astrophysicist, just to get a feel for how hard I'm shredding real physics.

Re: Coolant [Spaceships]
 

Once you're at privileging a frame of reference, you run back into the pre-relativistic implications of stuff not being at rest relative to the ether. If you're speed limited in a particular frame of reference, you can go over to a place where the local masses of note are moving at high velocity relative to that frame, and stuff winds up being really weird. That's why people often try to have speed limits somehow be tied to nearby gravity wells...

Though to be fair if you don't have FTL as well, traveling far enough from home for that to come up might be prohibitive.

Re: Coolant [Spaceships]
 

Some GMs tell me that they struggle to get players to read more than one A4 side of background material — about 800 words if you use small type.

I am a brutally verbose GM, demand that my players read 9,750 words of introduction to my SF setting, and find that that definitely deters some players who are otherwise keen.

How much do you want to ask your players to read? Of that budget, how many words do you want to invest in spinning a tissue of nonsense that sounds like physics? Every word you write about unknown subatomic forces found in meta-stable alloys of super-heavy post transuranic elements is one less word that players will read about Nexus 7 bioroid ninjas.

In the player's introduction to my interstellar SF setting, here is the whole text of what I wrote about the FTL drive:

An Eichberger drive allows a starship to travel at 1,000 times the speed of light.

If a player were to ask me "in what frame of reference?" I would answer "let me tell you about the parahuman elves and dwarves on Beleriand, and why they have orcs." If the player said "relativity, causality, and FTL travel: you can only pick two!" I'd say "I choose causality and FTL travel. Let me tell you about Nahal, the planet where they don't believe in men and women."

Right now the PC in my campaign is travelling under cover as a consultant bathyscaphist on a sailing ship on Paradise I, and he has just figured out that the crew are plotting to mutiny after he recovers the McGuffin from the deep. His mission being (1) to make sure that the cabin boy comes to no great harm, and (2) to plant certain fakes among the archaeological material recovered from a wrecked space-ship. The player has things to do that are more fun than picking the holes in technobabble. He would rather figure out why his mysterious bosses care about an innkeeper's orphan on a backwater planet than what frame of reference is privileged in the workings of Galactic Spaceways' liner operations.

Re: Coolant [Spaceships]
 

You've kind of centered 'I'm not interested in spaceship maneuvering and don't want my players to be either' there. Which isn't necessarily something you'll find total agreement with...

Re: Coolant [Spaceships]
 

That's fair criticism....

If I were interested in space opera then I would describe the relevant capabilities of spacecraft, perhaps in terms of some sort of game rules, and still avoid the technobabble. That might involve such statements as "to engage warp, a starship must have enough kinetic energy to be gravitationally unbound, i.e. travelling at system escape velocity" and "when a starship materialises out of warp is is stationary with respect to the barycentre of the system; how close it is to the desired exit point is determined by MoS on the astrogator's skill roll", and "spaceships are built using TL10 limited-superscience fusion torch reaction engines per Spaceships p.23."

That sort of thing is the cool content of a game centred on spaceship manoeuvring, its cyber-pirates and techno-ninjas. It is still the case that every word you write about how forcefields allow the fusion rocket to produce exhaust velocities above 9 km/s without temperatures above the sublimation point of graphite comes out of your budget for pirates and ninjas. Besides which, if your experience it anything like mine, all technobabble is either laughable gibberish to the players who studied physics, or else it allows them to drive a gold-plated Rolls-Royce through the loopholes it creates.

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."

My advice remains that you ought to minimise the technobabble, and write as little as possible about the ways your setting violates relativity etc. A sci-fi setting is a magic trick, and it is best not to draw readers' attention to the sleights of hand. Save your word count for the cool content, and direct reader's attention away from the bits that challenge suspension-of-disbelief.

Re: Coolant [Spaceships]
 

That's great from the point of view of gms and sf writers. I cringe in reading Asimov's older robot stories where he talkes about vaccum tubes and such. The more readable stories today just said "it's a robot" and went on with the story.

Re: Coolant [Spaceships]
 

As a counterpoint I've never had a player who said "Boo" about relativity.

The closest I've ever really come to interest in technobabble was one who thought it was sort of cool that the ship carried water in it's tanks and that it split that into hydrgen and oxygen with the oxygen going to the matter converter in main propulsion while the hydrogen went to make all other required superscience.

Of course, that was the player who didn't work with computers. Everyone else does do that to some degree and since i don't I never say anything about how computers work in my SF games. One of those guys did think it was cool that his TL10 wristwatch had an exabyte of storage space.

Re: Coolant [Spaceships]
 

I have pointed out that a particular interstellar travel system was rather dubious in terms of General Relativity, but I've only done this in-character, as a character who'd been created as an expert on it. Since a mystery was emerging that was clearly to do with malfunctions of the system, I regarded this as helping the GM, and they seemed to take it the same way.

Re: Coolant [Spaceships]
 

I think I might mostly agree in slightly different terms: It's important that it be understood how setting technology works at the level that the gameplay engages with it.

In most games that will range from 'customer' (only cares about the broad results and maybe the price) through 'advanced user' (needs to know the behavior in detail so that they can use or abuse it in special circumstances), with maybe some forays into 'technician' (some knowledge of what's in the box and what happens if you mess with the components). This can vary between different kinds of tech, and different play groups using the same setting are likely to have different priorities.

It's probably very rare for a game to actually want to deal with tech, especially superscience tech, at what I might call 'engineer' (advanced knowledge of the effects of all the components, and how they work together to produce the device behavior) or 'scientist' (can explain the principles by which the finest level of components produce their effects) levels. Even if the PCs do work on that level, the people at the table probably won't.

Re: Coolant [Spaceships]
 

Of course, an interesting application would be coolant for FTL. If normal radiators have diminished functionality during FTL, then venting coolant may be the only way to survive FTL travel. Strangely enough, this may also function as a fuel tank multiplier situation if the FTL 'impulse' (and the waste heat) is reduced by the reduction in mass.

If we assume one component of coolant is vented per three parsecs traveled, with a speed of three parsecs per week, then we end up with a situation similar to Traveller (smaller systems allow for slower travel). Coolant depots will be a valued part of any system and any spaceship without refineries will depend on them for survival. Emergency FTL systems would presumably take up one space and include a FTL drive capable of traveling one parsec per day, an emergency power plant capable of powering it, and enough coolant for one week of travel, allowing them to travel up to one parsec.

Re: Coolant [Spaceships]
 

What kind of emergency would that be useful in? For reference, the nearest stars to Sol are more than one parsec away...

Re: Coolant [Spaceships]
 

One parsec per day and seven days of endurance gives a range of nearly 23 light-years. In my setting the average nearest-neighbour distance of inhabited planets is about sixteen light-years.

Re: Coolant [Spaceships]
 

This is true, and I overlooked the self-inconsistency in the post. However, the part of it that's incompatible with the rest of the paragraph is the "one week of travel", not the "up to one parsec" conclusion.

Re: Coolant [Spaceships]
 

I'm going to assume you mean the emergency backup FTL is meant to travel one parsec per week, as otherwise your math doesn't add up and there's no reason to use the "main" FTL drive, which vents more coolant to travel at less than half the speed of the "emergency" FTL drive. This brings back the problem that you may be rather unlikely to find yourself within 1 parsec of a spaceport when you have a problem that disables your main drive. Using that 1 parsec reach to get back onto a major shipping route may be doable, however, after which you're drifting with a distress signal, hoping someone will stop and help.

Re: Coolant [Spaceships]
 

Lucky you. I've been grilled at length about how and whether my suggested star drives conserve energy, momentum, angular momentum, and baryon number, lectured about how they enable closed timelike paths, and ambushed with calculations about the effect on them of the galactic gravitational field, by five players with relevant advanced degrees. And that's not including using quantum mechanics to calculate the speed of a kind of stutterwarp drive that I didn't even suggest, calculating the blue-shift of light reflected by a light sail, and calculating the explosive yield of submunitions in an RKK weapon.

I've had a geography student challenge me about the population of a planet, two linguists go off for months about linguistic diversity, three lawyers argue about details of the laws and court procedures, a statistician calculate the minimum suicide rate among Imperial heirs that could be distinguished from baseline, and an economist engage me in a searching inquistion about the Imperial budget and the financial economics of the Imperial crown.

The linguists are a particularly interesting case, because they played happily for years in the setting while it had no representation of multiple languages. But they cavilled sharply when I added a couple of sentences to the history explaining about a couple of centuries of language loss on Old Earth, early colonies getting diverse immigrants with International Standard as their language in common, late immigration from the monoglot Earth of 2350, and the importance of references and recorded materials in Standard during the Age of Isolation. They were happy with a universal language until I tried to explain it.

Re: Coolant [Spaceships]
 

Are you in a University town? That all sounds terribly diverse. Ther closest I've come is a wide variety of computer geeks. Plus the many college students from back in the day, a lady with a Bio degree who did hazmat for NASA, a couple of house moms, a retail clerk, a nursing student and a travelling salesman. No, the travelling salesman isn't interested in math either. He uses GPS for route planning. I'm not even sure he'd get the joke I was trying to sneak in there.

Anyway, when it comes to interest in geeky detail; I've got jsut a couple of people with something like my compulsive reading habits but mostly just for urban fantasy these days. Beyond that and computers that it's pretty much taken as a given that I have more details about "stuff" then anyone else really wants to listen to.

Re: Coolant [Spaceships]
 

Not any more, but my roleplaying circles back in the day were formed on campus at the University of New South Wales and the Australian National University.

Re: Coolant [Spaceships]
 

Back in my hometown, we have a gaming group at the local college that's almost forty years old, and we still have some of the original members drop in on occasion. With fifty active student members and around a thousand alumni, it is quite easy to get a game. I would run two games a semester and be beating people off with a stick, and I was only the third most popular GM (the most popular was running four games a semester).

Anyway, I think I like the coolant idea for FTL more and more. Combined with a gravitation exclusion zone equal to (40 × [square root] of objects mass in Sols]), you end up with the edge of a system being a very busy place. The majority of the action would occur within 1 AU of the edge of the exclusion zone (to prevent suprise FTL attacks) where the refueling depots would be located due to access to volatiles.

Pirates and smugglers would have their own refueling depots in interstellar space, protected by anonymity and by distance, and they would prey on ships as they came out of FTL and run before the authorities could catch them. Of course, the authorities could easily come knocking, so most such depots would be temporary, just operating for a couple of months before relocating a couple of light months away. Abandoned depots, with buried cargo or hidden nanostasis hostages, would be a prime adventure location.

Re: Coolant [Spaceships]
 

40 whats? If that's AU, it's way out of the system at about the average distance of Pluto from Sol, and the shell of that sphere is huge it will only be busy at points close to something useful.

Ships coming from standard origins will arrive from known directions and unless your FTL system dumps them out in unpredictable places, will be able to arrive close to their intended refuelling point (but on the FTL boundary of course), which means the local law will be able to provide protection. If they arrive too scattered for protection by the law, how are the pirates able to predict their arrival points well enough to catch them?

If FTL paths are trackable from normal space, and/or FTL journeys can be interdicted it becomes easier for the pirates, of course.

Re: Coolant [Spaceships]
 

Of course, it also becomes easier to intercept pirates or pursue them back to their bases.

Re: Coolant [Spaceships]
 

But note that Jon's Law in is play now, as we saw in just that instance. Two diverted airplanes brought down the Twin Towers fairly effectively.

But on the other hand...we've had jumbo jets since the 1960s. The use of such as weapons has always been possible in all that time. There are lot and lots of planes in the sky, and have been for many years.

(After 911, when air traffic was temporarily grounded, the atmosphere as seen from space was noticeably clearer. There are that many contrails.)

In all those decades, with all those planes in play, it took almost half a century for somebody to actually do it on a big scale.

There are reasons. Security and air traffic control was good enough to make it a fairly unrewarding goal, it's hard to do it without killing yourself in the process, and most people aren't suicidal, and there are easier ways if your goal is a big disaster with a high death toll.

That same sort of consideration, it seems to me, could apply to interplanetary travel. Yes, a fast interplanetary ship is a WMD, but actually using it as such has a number of practical difficulties. It takes a lot of time, it's easy to see coming, etc. My hypothetical 100 kilometer/sec ship would need almost 3 hours to get up to speed at 1G, 30 hours at .1G, 300 hours at .01G. It would be detectable by radar and quite possibly glaringly visible, depending on the drive, in all that time. I'm not sure Jon's Law is that enormous a problem at this scale.

Now, if we start getting up to significant fractions of c, or ships with immense mass, Jon's Law starts to bite hard. Once we get north of .1c, we're starting to talk world-wreckers.

The hypothetical Daedalus probe, for ex, if it struck a habitable world at its cruise speed of .12c, would be a monster. We're talking many hundreds of gigatons, at least. Probably more power than the combined arsenals of both superpowers at the height of the Cold War (about 60 gigatons IIRC).

Re: Coolant [Spaceships]
 

No, it doesn't. Or at least, it doesn't have to, and having it do so would make it pointless.

The vented coolant isn't providing the thrust, it's carrying away the excess heat from the propulsion system. It's a consumable, but there's no reason to assume it's consumed at the rate that propellant would be in a rocket. The rocket equation is specific, it relates mass of propellant, mass of everything else, and exhaust velocity to produce specific results. If you know the exhaust velocity and the desired delta-V, it locks in a particular mass ratio. If you know the mass ratio and the exhaust velocity, it defines a specific delta-V.

If 100 tons of coolant keeps the magical drive working for (say) a week, that result isn't required to follow the rocket equation. If the consumption of coolant scales independently of velocity change, you're no longer living under the Tyranny, even if your magic drive is still limited in how long it can run.

Re: Coolant [Spaceships]
 

This is approximately my approach. It has several advantages.

I also assume that new forces and technologies exist that make standard rockets more efficient, boosting their effective exhaust velocity one way or another. This too has advantages.

Re: Coolant [Spaceships]
 

How worried should I be about all this for a setting with engines that resemble those of The Expanse, which for example appear to be capable of burning at 1G all the way to Saturn and back without refueling, and the ships don't seem to be made of fuel tanks.

Re: Coolant [Spaceships]
 

Seriously, right in the OP:
"Since the thrust required for sustained acceleration would decrease as mass decreased, coolant would effectively function like reaction mass (for example, 10 components of coolant would allow for 14 days of thrust at 1g). When a spacecraft runs out of coolant, it suffers 10% of HP for every combat turn that it continues to maintain thrust, as the waste heat causes massive damage to the drives."

Yes, applying the Tsiolkovsky rocket equation to the reactionless-but-delta-V-limited drive has the effective exhaust velocity you would use in the equation not actually corresponding to the velocity of anything in the system. But the equation still works exactly the same way.

In particular, the coolant consumption, per that quote, does not scale independently of velocity change (whatever you're thinking that might look like) - it in fact is consumed at a rate proportional to the thrust generated, exactly like reaction mass.

Now, does that make the idea pointless? Probably, yeah. Lots of us have said so, starting with the first replies to the thread. Myself included...
I'm sure the ships in The Expanse are very, very capable of playiing the part of hyper-velocity kinetic-kill missiles. I'm seeing somebody saying a test flight (gone wrong) hit 0.05 c in that? Yeah.

Re: Coolant [Spaceships]
 

Good book series, terrible science. Oh, we are going to steal energy from the Big Bang to power drives now. Oh, don't worry about causality, the theft will magically not change the present in any appreciable fashion. It would have been better had the drives stolen the energy from hyperspace or subspace, as it would have literally been more realistic (we have a fair idea of what should happen if you mess with the past, we have no idea of what should happen should you mess with another level of reality).

Re: Coolant [Spaceships]
 

All they said was the drives had much better efficiency than expected.
5% of c also works if you want to use the same drive to go to Saturn and back under a 1G acceleration.
Of course if the numbers end up with a ship that needs only a couple of fuel tanks, usually runs at 0,5G or 1G but can be pushed to 10G or even 20G, and can also be fitted with 5 times as many fuel tanks, then it's possibly a threat.
However, that's what 's expected give the setting.

Re: Coolant [Spaceships]
 

Just some cases looking at the possible situations that Reactionless Reaction drives:

A) Heat proportional to thrust: Spaceships generally travel at thrust levels that can be managed by their radiators, though are capable of very high levels of thrust in a pinch. Combat focuses on smashing enemy radiators to limit enemy mobility. Ships can accelerate forever.

B) Heat disproportionate to thrust, but low heat drives are possible: Clear division between fast moving clippers that need regular coolant refills, and slow moving tugs that rely on radiators. Carrier-Fighter configurations seem reasonable, with Fighters losing high heat drives for maneuverability, and carriers using low heat drives to travel long distances. Ships can accelerate forever.

C) Heat disproportionate to thrust, but low heat drives are impossible: Ships are limited to sites that have good supplies of water. Radiators are still relevant as they can increase the efficiency of engines (if you reject even a small fraction of the heat, you can avoid using coolant as fast you would otherwise). Ships cannot accelerate forever, but they still could accelerate really fast depending on effective exhaust velocity.

Re: Coolant [Spaceships]
 

Of course if you have a power plant that will get something up to planet cracking energies in less than a lifetime, it's not much of a threat to an equally capable target who have prepared for it. With that kind of energy to work with they can emit a radar pulse that will image it light-days out, which they use to target the beam weapon that will flash it to plasma in milliseconds at that same range.

You really do need to ignore the other things a civilization could do with vast energies to make it a center stage threat, probably starting with all the other more efficient ways we haven't thought of yet you could apply vast energies to devastating planets.

Re: Coolant [Spaceships]
 

Yes. There is a reason for the tradition of writing the equation and reporting performance in terms of specific impulse and not exhaust velocity. It's perfectly possible to apply slightly modified versions of the "rocket" equation to things like jet engines and helicopter rotors. You can get specific impulses that correspond to "exhaust velocities" greater than the speed of light when you do. Obviously nothing is actually moving anywhere near that fast, you are just using something other than the burned fuel to provide the momentum.

You don't need to consume a coolant to describe a reactionless thruster in terms of the rocket equation. If it consumes power you can compute a specific impulse in terms of consumption of whatever the power plant uses for fuel.

Re: Coolant [Spaceships]
 

The number of strategic warheads I have was 30,000. The great majority of the US contribution was 1/3rd megaton warheads on Minutemen. The W84 I believe. The only US warheads larger than that would have been soem on the rather small Atlas and Titan fleets and on SAC bombers. This number was never very high compared to the Minutemen even before they went MIRV.

So I think your number is a considerable overestimate even allowingf for larger Soviet warheads.

The rating for any c fractional vehicle is easy to calculate. It's the square root of the velocity in %c x the mass in antimatter equivalent. At c it would be 100% antimatter equivalent and you've spent the equivalent of the vehicle's mass in a 100% conversion drive to get there. C is where the Einstein equation (e=mc2) and the KE equation (ke=mv2) intersect.

So 12%c gives you 3.46 x the mass in antimatter with every metric ton of antimatter equivalent equalling 43 gigatons of TNT.

A quick google on "Daedalus probe" gives a scientific payload of 500 tons so that's 1.73 teratons rather than gigatons.

Re: Coolant [Spaceships]
 

E = ½mv² is the non-relativistic approximation for kinetic energy, which is not good to use for objects colliding at a significant fraction of c. And even in that energy is proportional to the square of velocity, not the square root of velocity. The expression for kinetic energy in special relativity is

E = mc² {[1/√(1-v²/c²)]-1}

That increases without bound as v → c (goes to infinity at c, not to mc²).

Re: Coolant [Spaceships]
 

Nothing specific to add, except that Project Thor had one massive flaw:

Project Damocles is a much better name.

Re: Coolant [Spaceships]
 

Provided that it dumps spent batteries or whatever rather than carrying them as a dead load, and has its performance improve as the load lightens.

Re: Coolant [Spaceships]
 

Yeah, the actual requirements for the rocket equation to work are that a specific quantity of lost mass produces a specific total impulse. The details of how the mass is lost are unimportant, but the rocket equation is just the solution of the integral dV = K*dM/M (where V is velocity and M is mass), so it doesn't work if K is not a constant or the thrust equation doesn't match the above.

Re: Coolant [Spaceships]
 

The rocket equation does not apply to an electric car travelling along a highway with rolling resistance, aerodynamic drag, and a speed limit.

Re: Coolant [Spaceships]
 

That's two separate issues. One is that the rocket equation only measures delta-V caused by the rocket, not from other sources, and the other is that vehicles that push on an external medium have variable performance based on speed relative to the medium they're pushing on.

Re: Coolant [Spaceships]
 

I count four issues. The battery doesn't get significantly lighter as it discharges. Speed doesn't change when force is applied to overcome resistance. Aerodynamic drag varies with speed. Electric motor and transmission efficiency vary with speed.

People sometimes assure me that Tsiolkovsky's equation applies to a hovering helicopter. Not if Δv = v(final) - v(initial) it doesn't.