[Suicide Junkie]

I think that with knowledge of shields (or armor) and the "x destroying" tech, you should be able to build defences against such weapons.

If different types of shields would stack properly (eg. phased & non-phased) then a low efficiency (eg. 5hp/kT) tachyon shield should be possible.

At least there is a method of defending against those attacks, which I really like.
Basically it involves decoys.

With a "Tachyon Dampener I", it does no damage at any range, but it is technically a weapon, so tachyon weapons have a finite chance of hitting it. It is also tough enough to resist most tachyon hits (although a massive mount TPC will still destroy it)

This way, with a WMG and 4 tachyon Dampeners around it, each tachyon hit has only a 20% chance of killing your WMG, and 80% chance of being absorbed by the TD.

The same could apply to engines (after elimination of engine limits eg. by making larger ships require 5/move), and shields.

You don't become immortal, but also don't lose all your weapons/engines/shields on round one of combat.