I know it's only Saturday but I wanted to get this down now and polish it later.
Regarding Traveller's M-Drives and J-Drives I came up with the following. Note NONE of this is canon. But I like it.
Both drives are related. The forces an M-Drive generates are used in the J-Drive to turn a micro wormhole into a macro wormhole.
The M-drive also generates matter as it operates, WIMP particles, which balance the momentum generated by the drive (The New Law is the conservation of Matter/Momentum.) Around a planet (within the hundred diameter limit these particles annihilate themselves continuously and produce the light and heat associated with thruster plates. In empty space running the M-drive causes them to build up. The longer you're under accelerations the more energy you throw into the field. The particles travel with the ship and reach a sort of stability in zero-g. Entering a gravity well screws this up and fast so ships spend a few extra hours moving tangent to their destination world to bleed this energy off. Otherwise, they can cause an explosion and damage the ship. A ship moving at relativistic speeds will burn up before it gets near a world.
Another side effect of the M-drive is that computers do not like them. Some of the early STL ships were built with their computers next to the engineering deck and suffered repeated malfunctions. Some were lost due to this effect. Ships today are built with their control centers are far from the M-drives as possible. Therefore you have ships with the bridge fore and the engines aft.
Another side effect of this is that small ships with high powered engines can't be operated solely by computer. They need a human operator so starfighters and launches need human pilots. Missiles use exotic rockets to allow their guidance to function.
Jump drives have a similar effect. After breaking out of jump space the ship's computers are reset. In fact exiting jump space also disorients organic minds. You can overcome the effect with experience and some drugs minimize the effect. In general you want your command crew away from the jump drive when you break out to minimize their disorientation (especially since your main computer is shut down or rebooting.) So we have the bridge and computers as far from the drives as possible.
A jump drive uses most of its hydrogen fuel to hold the wormhole open and create a safe bubble for the ship. The higher the jump number the more pressure exerted on the wormhole and safety bubble and the more hydrogen you need. Early drives can also require more hydrogen. Super refined fuel uses nano materials to maintain greater stability in the bubble.
Letting materials heavier than hydrogen contact jump space is a bad thing. They break down almost immediately into hydrogen and release a lot of energy, possibly destroying your ship. If a ship's safety bubble collapses it disintegrates into superheated plasma.
M-Drives and grav plates also generate wimps that are flushed out of the ship and stabilized using hydrogen. A ship with its artificial gravity and thrusters turned off could operate indefinitely as most of the hydrogen 'fuel ' never even sees the ship's fusion reactor.
Hydrogen from the safety bubble escapes when a ship breaks out . The relatively heated gas creates the jump flash