Exploring Efficient Weapons in Sci-Fi Settings

[DaveC426913]

I think the length of a battleship can be a km, but not the cross-section.

So now you need enough sensors, computers and weapons and fuel onboard your ship to locate, track and fire upon all those incoming rocks that track within that a half square km or so cross section. Which means you need a bigger ship than if you didn't need those things...

 

[GTOM]

So now you need enough sensors, computers and weapons and fuel onboard your ship to locate, track and fire upon all those incoming rocks that track within that a half square km or so cross section. Which means you need a bigger ship than if you didn't need those things...

Actually i think about an acre cross section.
The main laser is pretty fine to illuminate debris. Sensors don't have to be all onboard.
Well, an advanced defence system is even better.

 

[member 656954]

Actually i think about an acre cross section

Are you assuming the rubble is coming head on? Because it needn't be and ideally your foe would be aiming for the largest cross section of your ship.

 

[GTOM]

Are you assuming the rubble is coming head on? Because it needn't be and ideally your foe would be aiming for the largest cross section of your ship.

Not if you face them. Although i also think, if kinetics play an important role, that favors lots of smaller ships instead of big capital ships.

 

[DaveC426913]

Not if you face them.

Again, this is predicated on the assumption that
1] you have sensors that can pick up marble-sized objects at enough range to do something about it, and/or
2] there's only one attacking position. If the attacker can flank the defender then the defender will come up short on "faces".

 

[GTOM]

Again, this is predicated on the assumption that
1] you have sensors that can pick up marble-sized objects at enough range to do something about it, and/or
2] there's only one attacking position. If the attacker can flank the defender then the defender will come up short on "faces".

If the enemy has superior numbers, that is bad. Otherwise each ship face one attacker.
Each can have recon probes too. Maybe motherships even fighters, so they can target the butt of incoming missiles, and turn them into shrapnel very far away.

 

[member 656954]

Not if you face them.

Adding to @DaveC426913's observation, you are assuming that you can face them. I'm not sure that you are adequately visualizing how 3D warfare might happen, @GTOM. You can be readily bracketed by rubble coming from many directions in space, and if you are close to planets or large moons, then their gravity wells can be used to fling rubble at you from over the horizon. And again, these can be really small fragments, traveling very fast. They will be very hard to spot!

But I am still not sure if we are discussing the real-world physics of space warfare, or the "whatever goes" science-fiction physics of stories? They really are different beasts and the OP noted "hardish" sci-fi was their goal, so I've been applying that.

 

[GTOM]

Adding to @DaveC426913's observation, you are assuming that you can face them. I'm not sure that you are adequately visualizing how 3D warfare might happen, @GTOM. You can be readily bracketed by rubble coming from many directions in space, and if you are close to planets or large moons, then their gravity wells can be used to fling rubble at you from over the horizon. And again, these can be really small fragments, traveling very fast. They will be very hard to spot!

But I am still not sure if we are discussing the real-world physics of space warfare, or the "whatever goes" science-fiction physics of stories? They really are different beasts and the OP noted "hardish" sci-fi was their goal, so I've been applying that.

1. Realistic engines can maintain miliGs of acceleration for long time.
If you randomly throw rubble, the ship only has to face 1-2 of them at most. The main laser is great for illumination, fleet formation and additional recon/fighter craft can solve the rest.

2. If you fire guided missiles their thrusters are pretty bright, that makes it easy to estimate trajectory (they can't maintain acceleration for long time without nuclear power source) and deploy countermeasures, face toward them.

With the miliG order of sustainable acceleration, closing speeds are a few hundred km/s in deep space and much less in orbital combat.

 

[trurle]

1. Realistic engines can maintain miliGs of acceleration for long time.
If you randomly throw rubble, the ship only has to face 1-2 of them at most. The main laser is great for illumination, fleet formation and additional recon/fighter craft can solve the rest.

2. If you fire guided missiles their thrusters are pretty bright, that makes it easy to estimate trajectory (they can't maintain acceleration for long time without nuclear power source) and deploy countermeasures, face toward them.

With the miliG order of sustainable acceleration, closing speeds are a few hundred km/s in deep space and much less in orbital combat.

The problem should be evaluated actually as two separate problems
1) Defense against coasting threats.
*only active sensors with Detection_range=power^0.25 rule (laser/lidar, radar) are useful, therefore point defense only
*tradeoffs between defender energy budget on (maneuverability)/(point defense), (attacking swarm density)/(penetration capability of each element of swarm)
2) Defense against maneuvering threats
* Passive sensors can be relied upon, therefore area defense instead of point defense.
* Larger attack vehicles are generally not vulnerable to point defense (especially if point defense is laser-based)
* Tradeoff is between interceptor/attacker maneurability ratio, (interceptor range)/(interceptors amount)

Generally i expect category (1) threats to be more common in space-faring society. All you need for attack of type (1) is to dump enough mass of loosely constrained sort on right trajectory, and this capability is available for any spaceship. Category (2) threats are likely to be custom-tailored attack vehicles against specific (highly mobile) targets.

 

[GTOM]

Recon part: with advanced recon probes, you can pretty much decrease the beam scattering problem.

If the ship only maintain miliG s acceleration, i consider it mobile.

Laser focusing mirrors are vulnerable, so i think even a fighter squadron can use its lasers efficiently against bigger ships.
Of course with big distance the bigger ship still has the advantage, but it is possible to reduce distance in orbital combat.

 

[trurle]

Recon part: with advanced recon probes, you can pretty much decrease the beam scattering problem.

Sensor picket methodology. Well, it is not a very efficient protection. Because volley aimed at main ship can take out sensor pickets too. And pickets itself to be efficient must be outside of point defense range of mothership, therefore vulnerable to wider range of threats.

 

[essenmein]

With regard to the sensor topic and ships reaching relativistic speeds to be able to launch piles of rocks at people. If you can fly at those velocities, you'd better hope you have good sensor tech, because a stationary rock/rubble shield would be just as effective against you as the weapon you plan on wielding.