Changed to fit new J-Drive handwavium.
M-Drive works similarly to J-Drive in that it creates a bubble into 5D where the laws of gravity work differently.
In this case the M drive creates an M bubble in the core of the ship which allows the ship to *fall* in any direction it wants.
The power plant is required for the M drive to create the bubble but the M drive maintains the trickle of power needed to maintain the bubble after that.
Once created the M bubble lasts indefinitely with just a trickle of power.
The density of the bubble determines the maximum G.
In CT ships need 10Pn dtons of fuel for the power plant where Pn is the power number needed to to power the M drive for max G.
So a ship with an M drive that can create 4G needs a power plant with a power number of 4 also and so that power plant takes 10Pn dtons of fuel or 40 dtons.
In my handwavium it only takes Pn dtons to create the bubble (plus a trickle to maintain it). The 10Pn fuel requirement allows the creation of ten M bubbles.
So under normal operation a ship leaving to jump would fire up the M drive once (first go) till jump point, switch off (as imtu you can’t have M and J bubbles at the same time) and then switch the M bubble on again after the jump (second go) to port.
So 10Pn of fuel is like the amount considered safe rather than the amount used. If a ship only fires up the M drive twice on a trip then it will only use 2Pn.
Also if a ship has an M drive capable of producing nG then it can create bubbles of lower G that require less fuel.
A 2G scout would use 2dtons of fuel to fire up the M drive to create a 2G bubble or only 1 dton to create a 1G bubble.
A type T patrol ship with max 4G could use 4 dtons to create a 4G M bubble or just use 2 dtons and stick to 2G.