The Stars Our Destination

[jeff_wilson]

Originally Posted by David Johnston2

FTL drives don't help because you need space to accelerate.

There's usually plenty of room in other solar systems.

[Ulzgoroth]

Originally Posted by Joseph Paul

Losing a single decisive battle has huge downsides to it. Like extinction.

If the consequence of losing is extinction, how does the delaying action change that?

Originally Posted by Joseph Paul

Cost of collateral damage to the infrastructure of a system hosting mostly a small force is pretty negligible compared to losing a major manufacturing center with shipyards and personnel plus civilians to recruit from for the next battle....

Are you comparing collateral damage to defeat or are you proposing that collateral damage devastates the entire system?

In the latter case, that would be a reason to have a decisive battle one jump earlier, no more.

[David Johnston2]

Originally Posted by jeff_wilson

There's usually plenty of room in other solar systems.

I would be surprised if momentum is conserved when you've done something so non-Newtonian as a FTL jump.

[AlexanderHowl]

Well, C.J. Cherryh has FTL maintain velocity in her books, so it is not unknown in science fiction.

[Daigoro]

Originally Posted by AlexanderHowl

Well, C.J. Cherryh has FTL maintain velocity in her books, so it is not unknown in science fiction.

Relative to what frame of reference?

[AlexanderHowl]

The star system they are leaving and the star system they are entering. If I remember correctly, they have to be at a minimum of 0.9c before they can make an FTL jump. The acceleration and deceleration capabilities of the ships are quite impressive, around 100g, and they maintain inertia.

[Rupert]

Originally Posted by David Johnston2

FTL drives don't help because you need space to accelerate.

Yes they do - they let you accelerate in another solar system, and then jump, coming out already moving at dinosaur-killing velocity. Of course you need an FTL system that allows reasonably precise timing and placement of the exit point, and not too far away from the target planet (exiting 50AU out isn't going to let you surprise another star-faring culture, for example).

[Rupert]

Originally Posted by AlexanderHowl

The kinetic energy is equal to 1/2 (mass in kilograms × [velocity in meters] squared). A 1 million kilogram object traveling 577,000 meters per second would possess 167 PJ of energy, not even equal to Tsar Bomba. A dinosaur killer would be 500 ZJ, three million times as much, so you would need to accelerate a three billion metric tons (SM+21) object to 360 mps to do a KT event.

I did not say that the 1000 ton spaceship was a dinosaur-killer. I said that, given that a 1000 ton spaceship would be a multi-megaton impactor, spaceships could be dinosaur killers. You could avoid that by capping the mass of ship that the reactionless drives can move.

My current cheat is that the drives also lower inertia, and when turned off velocity reverts to that consistent with the ship's inertia. Remove inertia completely, you go FTL. Do that without paying attention, and you're likely to end up who-knows-where.

I find that an FTL exclusion zone of 10 AU around a Sol mass object has prevented any player from being too clever with kinetic energy objects, though it has not prevented them from using clever tactics against bases not protected by an FTL shadow. An FTL shadow allowed for defensive positions and safe zones, since people can see their attackers. It also served as a convenient plot point for preventing ships from escaping into FTL.

It also gives a couple of day's warning on an incoming hyper-velocity attack on your planet, assuming a Sol-like system, which is nice.

[Rupert]

Originally Posted by AlexanderHowl

The star system they are leaving and the star system they are entering. If I remember correctly, they have to be at a minimum of 0.9c before they can make an FTL jump. The acceleration and deceleration capabilities of the ships are quite impressive, around 100g, and they maintain inertia.

Deacceleration is even better than that, as they can cycle their FTL drive at lower power and 'skim' the border between normal and FTL space and that causes a sort of 'friction' that results in dump a great deal of velocity in a short time (and makes you 'skip' across a system, so you'd better hope there nothing at your 'landing' point).

[cptbutton]

Originally Posted by AlexanderHowl

Well, C.J. Cherryh has FTL maintain velocity in her books, so it is not unknown in science fiction.

Originally Posted by Daigoro

Relative to what frame of reference?

Originally Posted by AlexanderHowl

The star system they are leaving and the star system they are entering. If I remember correctly, they have to be at a minimum of 0.9c before they can make an FTL jump. The acceleration and deceleration capabilities of the ships are quite impressive, around 100g, and they maintain inertia.

Assuming you mean Cherryh's Union/Alliance/Chanur setting, I don't see it that way. My interpretation was it wasn't maintaining velocity it was creating it or sucking it out of hyperspace.

You undock from station and head out to the minimum distance from the mass (usually a star). This generally involves conventional thrust of not more than a few gravities for a few hours to a few days. You have to get far enough out, and get a velocity vector towards the target system, but not more than a few miles per second.

You turn on your jump drive and it pushes you into hyperspace. You travel through hyperspace until you hit a deep enough gravity field around a mass. Ships with a higher jump drive power to mass ratio can go faster than others and skip over smaller gravity wells. When you hit the gravity field it precipitates you out of hyperspace, but you have a real velocity of .7 to .9 c roughly towards the mass. You didn't pay for this kinetic energy, it came from nowhere or was extracted from hyperspace somehow.

If you do nothing then you are a menace, possibly smashing into other ships or the station*. Or the mass, but no one else cares in that case. Any gas/dust/gravel near your ship when you jumped ends up doing this at a smaller scale anyway. This can really annoy people, so be careful.

You could also crash into a planet as a dinokiller or even a moon-spaller-offer. A kif bad guy threatens this in the Chanur series. And one of the reasons Arian Emory backed the Gehenna project was that it created a secret nonthreatening planet for human survival if the Company War or sequel went apocalyptic.

But normally in the first hour or so you do 2-4 "v-dumps" where you flare your jump field to drag against hyperspace and slow you down. Like the main jump, this does not cause acceleration effects, although it does feel unpleasant. If you are in a hurry you can delay your v-dumps until you are close to the station, but this will annoy people.

After your v-dumps your are at normal system travel speeds (a few miles per second) and can proceed to the station with conventional drives.

[The Chanur books also seem to have something about protective force fields for ships, but it is scanty.]

* I haven't examined it carefully enough to run the numbers, but I suspect Cherryh has the common scale error problem of just not understanding that space is really really big, much bigger than you thought even though you knew it was really, really big.