Mach Drives

Scope and rating

A Mach Drive is a wearable inertial field generator: a Core, a Cell and a shaped field, the Envelope, mounted on the spine inside a frame. The unit couples its wearer to the local gravitational gradient instead of to the surface under their feet. Everything a Machborne does follows from that one substitution.

Every Drive carries a rating, a speed. It is the speed at which the foundry certifies the Envelope will still hold a body together under a hard landing. The first line's rating scheme gave the unit its name. Ratings are published as two numbers: the Break, where the Envelope changes regime, and the MachBreak, past which the foundry makes no promise. Operators quote the second. Quartermasters buy on the first.

Components

The Core. A sealed coupler core grown in a crucible over eleven weeks from a lattice seed. It is the component that couples the wearer to the gradient. A Core has no moving parts and no serviceable ones; it cannot be repaired, tuned or duplicated, and a Core that has been opened is a paperweight. Each is stamped with its foundry line and crucible number, and the survey services can identify a Drive from its coupling signature the way a port identifies a hull. A Core is worth more than the operator wearing it, and both parties know this.

The Cell. An energy store, and the operator's whole budget. The Cell pays for Burn, for shield projection, for the Lance and the Arc Thrower, and for some pack functions. Passive coupling, Traction and Glide alike, is free; the Core does that on its own. The Cell recharges from the frame's reactor at a fixed rate that does not change with the operator's circumstances.

The Envelope. The shaped field itself, roughly the volume of the wearer plus a hand's width, invisible except as a faint distortion at its edge under hard Burn. The Envelope is what takes the load. In a fall the skeleton feels the deceleration spread across the whole field volume instead of at the feet; in a hard lateral Burn it is the Envelope that turns and the body that follows. Its coupling coefficient is the one control the operator has that costs nothing.

The reactor and frame interface. The reactor is the frame's, not the Drive's; a Strider's reactor is small and its Cell-to-mass ratio high, a Bulwark's is large and moves a great deal of armour and a mortar. The interface is a certified spinal mount. A Drive moved between frames is re-certified for the new rating.

Coupling states

The Envelope's coupling has two set points and no useful ones in between.

Traction. Coupling high. The Envelope grips the surface as a body would, and the operator stands, walks, stops and turns like a person. Necessary for entering a Core Station, for firing a Lance, for repair work, and for the last ten metres of any run. Slow.

Glide. Coupling low. The Envelope is held just off the surface and the ground can push against it but cannot hold it. Friction falls to almost nothing. Gravity is unchanged, so a downhill face accelerates the operator and an uphill face decelerates them; the surface's shape becomes the operator's throttle. Bowls collect speed, ridgelines keep it, long descents build it, and every rise spends it. Glide is free. It is also the entire skill: the foundry can put an operator in Glide at the top of a slope, and what happens at the bottom is not the foundry's doing.

Switching between the states is instant and costs nothing. The foundry notes, for the record, that instant does not mean safe. A Runner who takes Traction at speed on a slope stops the way a body stops.

Burn

The Envelope can be shaped asymmetrically to push against the gradient. That push is a Burn, and the Cell pays for every fraction of a second of it.

Vertical Burn is the default and the first thing the foundry could certify: the Envelope pushes straight up the gradient, lifting the operator off the surface or slowing a descent. It is how an operator leaves the ground and how an operator arrives without breaking.

Vectored Burn is a trained skill. The operator shapes the push off-axis and pays more Cell per second for it, more the further from vertical. A lateral Burn bends a Vector in the air; a rear Burn is a brake; a forward Burn, the thing every initiate tries first, costs the most and gives the least, because it is trying to do terrain's job. The foundry's position is unchanged since Mach-1: Burn is for leaving the ground, correcting in the air and landing. Speed comes from ground.

Burn in the air is where the Cell goes. An operator who leaves a ridge on a Rise, corrects twice on the Burn Arc, and lands on Burn has spent, in the foundry's teaching example, roughly half of a full Cell in four seconds. A Runner who arrives at the enemy Core Station with two Burns left is a Runner who planned the Arc; a Runner who arrives with none has decided to be a pedestrian.

Energy budget

The Cell is one pool. It does not have compartments and it does not prioritise.

Draws on the Cell, in rough order of how fast they empty it:

• Lance discharge. A single shot takes a large fixed fraction. Two shots and a Burn is an ordinary operator's whole Cell.
• Vectored Burn, hard lateral. The Envelope is fighting its own shape.
• Shield projection (Shield Pack). Continuous while held; nothing else happens while it is held.
• Vertical Burn. The cheapest Burn, and the one operators spend most of their Cell on because they use it most.
• Arc Thrower. Continuous, moderate; heavy over a long engagement.
• Pack functions as rated: jammers, repair couplers, relay emitters.

Returns to the Cell:

• Reactor recharge. Fixed rate, always on, indifferent to what the operator is doing. An Energy Pack increases it.
• Nothing else. There is no way to recover Cell from terrain, from a kill, or from an objective. The foundry is periodically asked to add one and has periodically declined.

The operating ledger the foundry teaches is simple: a Cell spent on the ground is a Cell wasted, and a Cell carried into a Core Station is a Cell that did nothing. Spend it in the air, in the last third of the run, and arrive with enough to land. Everything else is style.

Empty. An empty Cell is not a dead operator. It is a Traction-or-Glide operator with no Burn, no shield, no Lance, at whatever speed the ground has already given them. On a good Breakline that is still a great deal of speed, and the foundry's records show more Cores delivered at zero Cell than at any other reading.

Regimes: the Break and the MachBreak

The Envelope behaves differently at speed. Below a certain velocity it is elastic: it flexes under load, which is what makes landings survivable and also what makes an operator at walking pace an easy target that stops when hit. Above that velocity the Envelope stiffens. The change is not gradual; the field transitions between regimes at a threshold the HUD marks with a line on the readout and a tone in the helmet.

That threshold is the Break. The word came back from the boundary zone with the salvage crews who first crossed it routinely, and the foundry adopted it because it was already in use.

Above the Break:

• The Envelope's stiffness makes the operator far harder to deflect. Hits that would stop a slow operator push a fast one a little off their line.
• Burn is more expensive and more effective; the Envelope is already under tension and the push has more to work against.
• The operator cannot stop. Traction at speed above the Break is a foundry-documented injury. The only choices are where to arrive and how much Cell to arrive with.
• Every telemetry channel records at full rate. The foundry wants the data. So does the ledger.

Well above the Break is the MachBreak regime: the Drive running past its rating, the Envelope at the edge of what it can hold, the operator faster than most weapons can be led. It is not a state the foundry certifies; it is the state past which the foundry stops making promises, and it is recorded, scored, and remembered. An operator who has held a MachBreak in sanctioned telemetry carries the Apex grade for life.

The two thresholds are published per Drive and per frame. Inside the boundary zone of the Break, the region that gave the regime its name, both come earlier and the Envelope holds past either. Nobody at the foundry can tell you why.

Failure modes

Listed in order of how often the foundry sees them. Every one of these is in the telemetry of at least one operator the foundry certified.

Cell exhaustion in the air. The commonest. A Burn Arc planned on the assumption of a Cell that is not there. The operator lands at whatever velocity gravity and the last Burn left them, and the Envelope takes what it can. Survivable below the Break. Above it, usually not.

Envelope overload. The Envelope has a load it can distribute and a landing can exceed it. Above the rating, or below it at a bad angle onto a hard face, the field collapses for a fraction of a second and the skeleton takes the difference. The foundry's rating is the promise that this will not happen on a flat landing at that speed. It is not a promise about walls.

Traction at speed. Documented above. An operator who takes high coupling above the Break is coupling a moving body to a stationary surface in a single frame of time. The foundry has interlocked this on training units and left it enabled on field units, because there are landings where it is the right call.

Cell fault. A Cell that reads full and is not. Rare on foundry Cells; commoner on Break salvage, which the foundry does not certify and cannot read.

Core fault. Almost unknown on a sealed Core, and unmistakable when it occurs: coupling drops to nothing, the operator is a person standing on a hill in a suit of armour, and the Core is a paperweight. The foundry has never confirmed a Core fault that was not preceded by the Core being opened.

Boundary overcoupling. A Drive in the Break's boundary zone couples harder than its rating and the operator glides further, burns harder and holds together past the MachBreak. The failure is not the Drive's. It is the operator's: a body that has learned one set of thresholds arriving in a place where they are wrong. Salvage crews call the first week in the zone "learning the ground again." The survey services' casualty figures for that week are not published.

Interference. Jamming does not touch the Drive. Nothing anyone has built touches the Drive. A jammer blinds the sensors the operator relies on and the HUD the thresholds are drawn on; the Envelope neither knows nor cares. An operator who can read the ground without the readout is an operator a jammer cannot slow.

Certification

An operator is certified by foundry grade, and the grades are the competitive ranks the ledgers use: Initiate, Certified, Rated, Field-Rated, Vectored, Breakrated, Apex. Certification is on a frame and a Drive line; a Ranger certification does not cover a Bulwark, and the foundry re-tests on re-mount. Washout rate is not published. The foundry's position is that a certified operator is a tradesperson with a dangerous tool, that most who hold the certificate are ordinary people who were good at it, and that the certificate says nothing about them except that. The word on the stamp is Machborne.

Break salvage

Drives, Cells and Cores recovered from the boundary zone carry the zone's coupling with them. A Break Core outperforms a foundry Core of the same line; a Break Cell holds past its reading. The foundry does not certify salvage, cannot reproduce it, and buys it at every opportunity. What it has established: the change is in the Core, not the Cell or the frame; it does not fade; it cannot be induced outside the zone; and a Break Core's coupling signature is readable by survey instruments as a foundry Core's is, with a component the instruments have no name for. Every bloc holds some. None holds enough. The Mach Wars are, in the foundry's accounting, a dispute over the supply of an object the foundry did not make.