If opening subspace portal and keeping them open is so cheap and easy - why aren't subspace portal always kept open?
The Knossoss opens up only when a ships is going trough. The shivan subspace opening aren't kept open for other ships to pass trough. Each ships creates it's own that closes immediately.
Perhaps because opening the portal is tremendously energy-expensive: thus why the Lucifer carries around five vulnerable reactors to keep its shield up at all times. (Ironically, multiple ships DID pass through subspace openings in the original game design.) But that doesn't tie the cost of opening and holding the portal open to the mass of anything passing through.
None of that is evidence against a flat-rate cost for holding a subspace aperture open based solely on duration rather than transit mass. I don't personally
believe that theory, but there's no way to disconfirm it.
And you still miss the point. What if you throw MORE mass/energy per second than the portal shield is capable of transporting? EVERYTHING in the universe has a limit.
A domain wall doesn't care how much baryonic matter you throw at it; it will happily convert it all into radiation. A singularity will eat a constant stream of whatever and just grow bigger (mass and energy are conserved); a wormhole would simply throw it all somewhere else.
The Lucifer's shield could (I say could, not 'is'!) be 'truly invincible' as long as it's up because it simply requires a flat rate to
stay on: everything that hits it goes somewhere else, but that process is not energy intensive any more than it's energy-intensive to throw stuff through an empty hole. The hole itself pays no price for the mass transit.
I'm not a big fan of this theory, but there is nothing in either physics or FSverse to suggest that Lucifer's shield can't be
genuinely invincible so long as it simply eats stuff and throws it out in subspace.
Personally, I think that'd be silly, but if a campaign wanted to argue that, there is nothing to prevent it.
