Coolant [Spaceships]

[Rupert]

Originally Posted by AlexanderHowl

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.

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.

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.

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.

[Ulzgoroth]

Originally Posted by Rupert

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

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

[Johnny1A.2]

Originally Posted by Agemegos

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.

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).

[Johnny1A.2]

Originally Posted by Ulzgoroth

The OP's proposal literally keeps the rocket equation in! The only thing it changes is not having a high-energy exhaust stream.

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.

[Johnny1A.2]

Originally Posted by Anthony

[*]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).[/list]

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.

[Aldric]

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.

[Ulzgoroth]

Originally Posted by Johnny1A.2

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.

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...

Originally Posted by Aldric

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.

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.

[AlexanderHowl]

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).

[Aldric]

Originally Posted by AlexanderHowl

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).

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.

[TGLS]

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.