I was talking with some folks on another forum, and the topic of BattleTech's fusion plants and (especially) rockets came up. Namely, how unrealistically powerful and low-maintenance they are. Now this is fine, it's part of the setting. But it got me thinking, to the point that I actually came back here and started a new topic (which I will hopefully not come to regret).
Here's what we know: fusion plants were developed. Kearny and Fuchida discovered anomalies in their power outputs, and from there formulated the mathematics that would lead to Jump drives. After Jump drives were invented and perfected, fusion plants became even better. Now, real fusion plants would produce a great deal of energy, yes, but still require a decent amount of fuel (far less than other methods, but measurable, and often exotic). While the mechanics of Jumps are, of course, shrouded in technobabble (since the entire process is science fiction and relies on Hypothetical Future Math), it's still clear that there really isn't another dimension that can be traveled to, but instead a sort of mathematical shortcut that allows direct physical translation from one place to another. It's not Star Trek teleporters, that destroy and recreate you, it's actual travel, just cutting out all the empty in-between. The start and end places are even called "points," which is a mathematical ideal.
So here's what the thread title is all about: they're not really fusion power plants and rockets. Fusion is powerful, but nowhere near THAT powerful. Indeed, fusion rockets should be really slow, or more properly, accelerate at a lower rate - just for a very long time and very efficiently. The fusion process is just a catalyst (heh) for an honest-to-Cat zero point energy system...and nobody in-universe realizes this yet, or at least it's a well-kept secret. Any BattleTech "fusion" plant could produce unlimited energy instantly (which would be a VERY BAD IDEA), but they're actually limited by the amount of shielding you give them, and power plants capable of handling cosmic levels of energy would be prohibitively large and expensive. A 400-rated engine produces 40 times as much power as a 10-rated, but weighs over a hundred times as much - which is another argument against them being true fusion, as that would be nonsensical. Real fusion would be more efficient the larger you got, until you had something made almost entirely of hydrogen and helium producing as much energy as the sun. Which would be a sun.
There you go. The biggest secret in BattleTech revealed: it's a post-scarcity economy, and this fact has been hidden away. I like to think that Jerome Blake made the connection while ill, and Toyama straight-up murdered him to bury this secret as deeply as he could. Layers upon layers - pseudo-mysticism, hidden councils, hidden worlds, destabilization campaigns, the deliberate culling of brilliant researchers...and perhaps a few crazies here and there who started poking around with an insane, impossible theory abandoned in the early 21st Century. Stone sees is as some sort Blakist super-shield, the Coyotes managed to use it as armor on a WarShip, and Apollyon was arrogant enough to weaponize it (we've still not seen stats for his personal 'Mech), but they still didn't know just what they were dealing with. The Master knew, and that's why he sent the core of the Word of Blake out of known space. He was evil and power-mad, but he would've ushered in a new Golden Age for mankind (under an iron boot), but in a way he was right. It's all too powerful for the Successor Lords and Clan Khans to be trusted with it.
(If this is The Secret, rest assured there was no leak from the developers; as I said, I came up with this on my own. If it's not, good luck coming up with something better. ;) )