The E wrote:It's a scale problem. In order to bring active defenses to bear against a c-fractional strike, you need to be able to detect it and boot your active defenses before the projectile does damage. This means that detection has to happen at a range of several lightminutes; a .99c projectile will be hot on the heels of the returning radar pulse, in order for a warning to be useful, it needs to come in a couple of minutes before the projectile is in range. In other words, detection needs to happen at 3 to 5 lightminutes at the latest, covering a shell that large with both sensor and defensive platforms takes time and resources.
It's not impossible to do this, mind you. It's just hilariously wasteful. Let's not forget, c-fractional strikes are incredibly rare, so you'd be expending massive efforts to guard against an attack that will probably never happen.
There are occasions where building such a defense system is justifiable. Grayson before HotQ, for example. But what occurs to me is that it's probably easier to build a navy to punch people preemptively (or to maintain a retaliation capability to act as a deterrent) than it is to try to maintain a supposedly impenetrable defensive screen.
And let's not kid ourselves here: Honorverse tech makes it incredibly easy to pull off attacks. No defense is absolute, and if an attacker is determined enough, such a defensive system would be only a minor inconvenience; after all, if you can launch one c-fractional projectile, chances are you're able to launch a hundred or a thousand or however many are necessary to overwhelm any given defense.
The basic serious system defense already employs a whole lot of sensor coverage, aimed not at the near-c ballistic attack near to the target, but at the hyper translation and impeller signatures way out. Spider drives particularly mean the impeller detection component can't do the work it traditionally has, and the incoming hyper translations of careful and patient people can be very hard to catch, to distinguish from noise or malfunctions, or to respond to before they get far enough away from the n-space entry point to be detectable.
FTL communications can help tremendously - they offer that hope of actually responding faster than a near-c attack as you see it coming in. But yeah, the scale to make a difference at that point is prohibitive. Beefing up the traditional defense, with an awareness of the higher threat level and stealth problems against spider drive units, is doable: you can get faster and more serious responses out of the light units checking out those slight hyper footprints, you can station them out at the hyperlimit with warm generators so they get there sooner, you can tie them directly to sensors out there to reduce the command loop, and you can emphasize detection by every in addition to gravitics.
Bolthole boffins may be able to help those sensors, and work out something to pick up spider drive usage too. There may be some application for dedicated recon drone tender destroyers to check out those footprints - not built to fight much of anything, but to be an economical platform you can build and maintain in bulk to check out those footprints ASAP and flood the suspect area with recon drones. (I'd call it a frigate if not for fear of bringing the wrath of RFC down.
But really, all the unit needs to be is a courier boat built up to support a load of drones and the gear to monitor and control them. If someone kills it, they've given up the stealth approach.)
If you have a suspect footprint, you could have some idea where a ballistic attack is coming from, and that could let you deploy mobile sensor platforms along that route to detect it. You could also deploy tugs or similar ships between that threat and likely targets - if you can put it in the right place, the impeller wedge will scotch any attack.
