waddles for desert wrote:For example, in an active system, there certainly is no need for a one-to-one correlation between emitters and detectors for each beam path. Assuming a continuous beam, an emitter can use mirrors, prisms or waveguides to illuminate multiple detectors. And, detectors can have multiple detecting surfaces to receive beams from multiple emitters.
Unfortunately, having each transmitter beam to multiple receivers only slightly reduces the total number of transmitters plus receivers necessary. The key factor in detecting ships with beams is that the beams must not leave any gaps very much larger than the diameter of the ships. So if you reduce the number of transmitters, you will have to increase the number of recievers to protect the spaces that would otherwise have been covered near transmitters. You can reduce the numbers somewhat, but it is still in the range of hundreds of millions to billions.
Each detector transmits to the nearest FTL relay. Adding FTL relays increases the cost and decrease the time lag of the report, and vice versa.
All the discussion so far has assumed that communication of a detection would be by FTL.
A cheaper system would be to use a glorified nano fiber spider web with flash bulbs. The cells of the spider web could be 100 m across. A wide angle detector would monitor for flashes and signal the FTL relay. A robot vehicle would keep the components on station.
Are you suggesting enclosing a 20 light-minute radius with a nanofiber web? That's quote audacious. It would certainly work, though I have difficulty imagining it being done even in the Honorverse. For your flash detector, you would have to balance the field-of-view versus time-lag. You would have to have the detector close enough to the web that you don't have too much time-lag in detecting the flashes.
All of this is expensive. But, compared to what was lost in OB, not so much. Not at all compared to what would be lost to a massive high fractional c strike.
Unfortunately, this system cannot really protect adequately against a high-fractional cee strike. It is designed to detect ship-sized objects. A cee-fractional strike would probably involve smaller objects. An enemy who sent only a few kinetic weapons through might be lucky and miss your detection network. Depending on how small the weapons were, they could get significantly better than 50% chance.