FTL Assumptions [Space]

[AlexanderHowl]

You are welcome. The best locations are Titan (atmospheric nitrogen), Triton (ammonia ices), and KBOs (ammonia ices). Other possible resources are water ice, methane ice, silicates, metals, etc. Since deuterium is around 1:20,000 by mass for hydrogen in the outer system, every metric tons gives 50 grams, which DD fusion turns into massive amounts of heat, electricity, and 18.75 grams of helium-3, so a civilization will never run out of fuel as long as it has ice.

In truth, any civilization that is capable of interstellar travel is approaching post-scarcity because of combination of low fertility rates and high resource availability, even without SAI labor. A TL10 civilization will probably have a 20 hour work week due to high levels of automation, with only the people on spacecraft working longer hours out of necessity (and to prevent boredom). With genetic engineering, they will also be stronger, smarter, healthier, etc., so they will just be better workers.

Since conflicts will likely not be over resources, they will probably be over biological reservoirs. Since it will be expensive to develop new life, it will be much cheaper to preserve existing life. New lifeforms will be valuable, especially if they are useful, and new worlds with unique lifeforms will be worth trillions to the individuals who possess their rights.

[weby]

Originally Posted by Rupert

Every hyperspace capable ship is a civilisation ending WMD with this system. The exit velocity gives a 1kg object kinetic energy of about 1-kiloton of TNT. Travel time from Earth's 100 diameter limit to Earth at 0.01c is a little over 7 minutes. Even an accidental loss of control by some freighter exiting hyperspace inbound is a civilisation-ending event.

Indeed they are, but only if they are intentionally used as such or by gross incompetence.

As normal entries are at 1500-1600 light seconds for most civilian ships(so that they can decelerate in time). And that is to low population systems. Also the official approach lines do not point directly at planets.

In high population systems normal ships are way less allowed freely to approach populated planets.

As example take the Capitol system(the imperial seat and highest population system in the empire), Inbound starships need to use certain approach lines and can only go to vicinity of the fifth planet in the system where the star port stations exist.

The 174 primary systems have similar policies in place, the secondary systems (17400) will have less elaborate things, but still usually going to a place far from the main inhabited planets. But things like colonies will likely have just assigned travel lines but not much they can do on attacks.

But incidents do happen, most of the accidental errors are just minor errors like the ship exiting at 1400 light seconds instead of 1500 so cannot stop in time and thus will need to go around for another go or in a too close to planet vector, but there is plenty of time to fix those at the normal distances.

It is the occasional deliberate attacks that cause the real problems.

1% of C gives an impact energy of about 1 megaton per ton of ship. That's pretty 'utterly devastating'.

Yes, except that in any civilized system the ship will be in small pieces by the time it hits the planet, any one ton piece is definitely shattered into much smaller pieces and those pieces into even smaller. The denser parts of such a ship like small pieces of armor materials will survive the atmospheric entry, but most of the mass of a ship will not.

In a colony system: yes definitely you can take out a city with such way too likely, but the total population of such places is such that while it is utterly devastating for the people involved, it is meaningless for the empire. The total sum population of all the about 530 000 colonies is 0.2% of the imperial total, so it would take thousands of such attacks to make primary worlds notice. (That is because the primary system people mostly think of colonies as dangerous with constant pirate attacks and such). And even then the notice would likely be in the form of harder recruitment of colonists and increased funding for local system defenses.

The most numerous tries for such terror attacks are however not by starships, they are by people trying to hijack local system craft as they are way more numerous and going to populated planets and thus easier accessible in major systems and as devastating if successful. Every year there are attempts in large population systems, and every time the sensationalist part of the press plays up simulations of what could happen if they succeeded.

Thus major efforts have gone to securing all in system ships in major systems. They have things like remote control of propulsion systems by traffic control that is really hard to bypass, multiple redundant beacons to transmit their course data, armored bulkhead between passenger and piloting compartments and so on.

As for deliberate attacks by military ships: Yes they are much more of a problem in a real war as they are much tougher and thus harder to stop doing suicide runs and in the past planets have been devastated by such attacks, and indeed one of the previous civilizations was broken by massed numbers of AI driven military grade ships doing such.

And all military planners definitely worry about such repeating and there is only so much they can do due to the fact that the empire has so many systems and a serious attacker could focus on single systems with overpowering strength.

But in such a situation the attacker would more likely not go for the effect as a few line cruisers over a planet once the defenses are neutralized can destroy everything on it really fast. Large warships(and defensive bases) in the setting are devastatingly powerful.

But in simulations there are cases where in a total war situation you could have a force that is powerful enough to push couple of ships through defenses and not enough to neutralize the defenses. But that would also require a major part of the ships crew to man the point defense weapons, EW systems and so on to allow the push though, without such crew the number of ships needed would go up a lot and thus in most cases be more efficient to do the slow deliberate attack.

[lwcamp]

Originally Posted by weby

Yes, except that in any civilized system the ship will be in small pieces by the time it hits the planet, any one ton piece is definitely shattered into much smaller pieces and those pieces into even smaller. The denser parts of such a ship like small pieces of armor materials will survive the atmospheric entry, but most of the mass of a ship will not.

It is not clear that breaking a relativistic impactor into small pieces will accomplish much. The stress of atmospheric entry will break up any spacecraft anyway (although very large ones may be shielded by their front ends well enough that part of the back can impact the ground - I have a vague memory that the last time I did the calculation you needed to be about Babylon-5 size for this). So you will expect these relativistic spacecraft to give high altitude airbursts ("high", here, being somewhere in the mesosphere or stratosphere, depending on the size of the craft). Breaking the spacecraft up into pieces also gives you a high altitude airburst. If the pieces have dispersed much, you will have the burst at higher altitude than otherwise. If they did not, then it will not make much difference - striking the atmosphere as a dense collection of aggregated fragments will give about the same penetration into the air as a solid object, since at these speeds the mechanical ram pressure is so high that mechanical strength is irrelevant and any material will flow as a fluid, whether a monolithic spacecraft or a pile of rubble.

At 1% c, even dense armor will not survive atmospheric entry (for earth-like atmospheres, anyway), unless, as discussed above, it was on the back end of a very large craft.

Luke

[lwcamp]

Originally Posted by Rupert

When deciding how I want my FTL to function, in terms of in universe effects and game mechanics, such things are just window-dressing anyway. I've already decided to do terrible damage to our understanding of physics by having an FTL drive that gives reasonably quick and convenient interstellar travel.

You can make it slightly more plausible. Rather than "planetary diameters" you could use a "causality exclusion zone" generated by the same tech that makes FTL possible in the first place. Preventing causality violations brings you up to a slightly higher level of hardness (although it is maybe only "firm" rather than the "mushy and runny" of using planetary or solar gravity). It also adds more tactical choices. If you can blow up the causality exclusion generators, you can warp in your troop ships and begin the invasion. You can have ship-board generators to keep pirates from getting away; the pirates can use causality exclusion mines to prevent their quarry from jumping out; shoot generator-equipped missiles around the battlefield to limit enemy maneuverability; and so forth.

Luke

[Rupert]

Originally Posted by lwcamp

You can make it slightly more plausible. Rather than "planetary diameters" you could use a "causality exclusion zone" generated by the same tech that makes FTL possible in the first place. Preventing causality violations brings you up to a slightly higher level of hardness (although it is maybe only "firm" rather than the "mushy and runny" of using planetary or solar gravity). It also adds more tactical choices. If you can blow up the causality exclusion generators, you can warp in your troop ships and begin the invasion. You can have ship-board generators to keep pirates from getting away; the pirates can use causality exclusion mines to prevent their quarry from jumping out; shoot generator-equipped missiles around the battlefield to limit enemy maneuverability; and so forth.

At this point space combat starts looking not unlike EVE Online, in terms of stopping ships leaving fights, having bubbles that can black their passage, and so on. This may or may not be a good thing, depending on what you're after.

[AlexanderHowl]

I generally think that any velocity above 0.001c is inappropriate for civilian spacecraft. Of course, that means that it takes a week or so per AU traveled, but that is better than having every spacecraft being capable of ending civilization. In fact, I can imagine a society deliberately limiting civilian spacecraft to the maximum velocity and destroying any civilian spacecraft that violates that limit with extreme prejudice.