How it works

How it works

What the game does, and what this mod does instead

The game gives every part a crash tolerance, a speed in metres a second. Whenever anything touches a part faster than that (the speed counted in full, along the ground as well as into it), the part is destroyed on the spot: its explosion is set off, it is gone, and whatever hung from it carries on as a separate craft until it, too, touches something. A rocket that comes down at a slant is destroyed part by part within a few tenths of a second where it first touched, and nothing of it goes on along the ground. (In the game's code: Part.OnCollisionEnter and OnCollisionStay both lead to Part.HandleCollision, which compares the speed with crashTolerance and calls Part.explode; the game's guard against a fast part passing through the ground between two steps of the physics, CollisionEnhancer, does the same.)

This mod does not patch any of that. It works through the one figure the game's decision turns on:

• Who may crash. Every step of the physics (fifty a second) it looks at each craft. One that is moving faster than its weakest part can take, and is close enough to the ground to reach it within about two seconds, is armed; so is one coming together with another craft that fast. An armed craft's parts have their crash tolerance raised past anything the game could measure, so that the game no longer destroys them, and each part tells the mod what it touches. A craft that has come to rest, or has nothing within reach, is given its own tolerances back.
• Over water nothing is armed: what a splash does is the game's.
• Paving or soil. What a craft touches is paving where the game tags it so (the runway, a pad, the grounds of each of the space centre's buildings) and soil everywhere else. The game tags the space centre's lawns as it tags its tarmac, so along the runway the mod looks at what is drawn: each section of the runway is one mesh, grass and tarmac blended by a mask, and the mod reads that mask under each part that touches (a dozen times a second): tarmac and the painted lines are paving; the grass of the runway's shoulders and the lawn beyond it is soil. (Since 0.2.2. The grounds round the buildings stay paving, lawns and all: what is drawn there is not what a craft touches.)
• A craft that touches down within its parts' tolerances is not hurt, as in the game. Only what is beyond a part's own tolerance counts against it.

A part's own skin

The moment a craft is armed, each of its parts' skins is cut into the panels it would tear into, on another thread while the craft is still falling, once for each kind of part (every FL-T800 shares the same panels):

• The part's meshes, as the game draws them, are taken into the part's own axes as loose triangles. This works for any part whose meshes can be read, from any mod: nothing is known in advance about any part.
• Every edge longer than a few centimetres is cut in two, the same way on both sides of it, and again, until none is (so that no corner of one triangle lies in the middle of its neighbour's side, which would open a crack in the skin when it is bent).
• Points are scattered over the skin, each with a size drawn so that there are few large panels and many small ones (the number bigger than a size goes as that size to the power -1.6, the fit NASA's breakup model uses: see Research), and each triangle goes to the point nearest it, nearer counting for more the bigger the point's panel; the borders wander a little, each panel's its own way, so that they are not straight lines. Each panel knows its triangles, its neighbours, and the edges it shares with each, which is where a tear runs. A tank's skin comes to about forty panels, most a few tens of centimetres across.
• An engine is not cut: its bell, its pump and its mounting each come away whole (what the ground does to a part like that is under The slide, below). Nor is a small mesh on a big part (a hatch, a ladder, a light): it comes away whole too.

From the first time a part is hurt, the mod draws it in place of the game: the part's own renderers are hidden and its panels are drawn as they now are, with what has happened to them (below), wherever a panel is gone the inside of the skin and its torn edges, as thick as the wall, and blackened where it burned (since 0.3.0 the inside shows the structure that holds a tank's wall round: a ring frame every 1.1 m up the part, its flange's lit edge and the shadow it throws down the wall, with lighter ribs between; painted on the inside as it comes round, so that it follows every dent and tear of the wall it is on). The part itself stays a part of the craft, joined to the parts beside it. As soon as any of its skin is gone its own colliders give way to the convex hull of what is left of its skin (so that a tank that has lost its underside sits lower, and a torn tank no longer rolls), set back into the ground by as much as it has dug in, and its mass goes down with its skin. Drawing a torn skin is the dearest thing the mod does on the game's own thread, so one part's skin is drawn torn for the first time each frame (a dozen parts hurt at once are all drawn torn within a fifth of a second), and redrawing skins that change again is held to about three milliseconds a frame on average (a part being ground along the ground is redrawn a few times a second).

A blow

When a part runs into the ground, the mod works out how much of the craft's energy goes into the ground at that point. Not the whole craft's: a blow at the end of a long rocket turns the rocket as well as stopping it, so the mass the blow has to stop there is less than the whole (it is worked out from the craft's mass, its middle and how hard it is to turn, as for any rigid body: see Body.cs). That mass, times the square of the speed into the ground beyond what the part takes unharmed, is what the part has to take.

A part's structure takes so much before it is crushed right through: half its dry mass times the square of its crash tolerance, times 35 (as set; "How tough parts are" scales it). What is in a part adds to the blow and nothing to the strength, so a full tank bursts sooner than an empty one, as real ones do. A blow crushes the part by that share of its length, at the end that hit: the skin there is pushed in, and folds as a thin tube driven end on folds (in rings, bulging out more than in); the panels flattened right down are torn off as crumpled pieces; a tank on its side is flattened from below. A small blow dents it. An engine's bell (since 0.3.0) crumples in short folds, as thin steel does when crushed (folds about 1.8 times the square root of its radius times its wall, under a tenth of a metre for a bell), a crumpled cone rather than a smooth dent: tried on the test rocket's Terrier, crushed 0.5 m in from one side. If it holds, the craft's going into the ground at that point is stopped, with a little bounce (an eighth of the speed), and the ground's bite takes some of its speed along it. If it does not, it is crushed through, and the craft goes on into the ground that much slower, for the next part to take.

A wreck does not bound (since 0.2.2). Once a craft has been hurt, or is a piece come off one that was, whatever speed away from the ground its middle has after a touch, beyond a tenth of the speed it came down at, is taken from it: what struck gives way, as thin structure does, and stays folded; it does not throw the wreck up again; and it loses three tenths of its turning at each blow, so that it tumbles and does not spin up like a wheel. On paving the ground's grip in a blow is the paving's friction on what the ground pushed back with there (where before it was a quarter of the small part of that which this mod itself stops), but on no more than stopping the wreck's own fall takes, and shared among the parts that strike in the same step: a wreck that tumbles along is held back at every strike, as one that slides is all the way. (Reckoned on how fast the corner that struck was going, the grip spun a tumbling engine up in two strikes and smashed it with the third, 26 m from its first touch: see What was tested.) A craft that comes down within what its parts take is not a wreck, and bounces as the game has it.

Every push is given to the craft as one rigid body: each part gets the motion it would have as a piece of that body. On soil, a hard blow leaves a crater (as wide as the cube root of the blow's energy: a metre for a gentle one, several metres for a hard one) with its rim thrown up, and throws clods of earth.

Two craft running into each other (in orbit, say): the softer of the two parts takes more of it, and a tank, a thin wall full of liquid, is pierced rather than crushed. Dragged along the other craft in a graze, the parts that touch are torn by the push between them times how fast they slide.

The slide

A craft lying on the ground and moving along it is slowed where it touches:

• On soil, by friction (half its weight) and by ploughing, which grows with speed and with how deep each part has dug in. A part digs in as it slides, deeper the further it goes (most of the way within a dozen metres), down to a quarter of its own width; dug in, it ploughs harder (twice as hard 18 cm down), and it sits down into the ground by as much. Torn open, it scoops the earth up and holds in it: as its underside is torn away, its ploughing grows to three times a smooth skin's and more (seven and a half times once two fifths of its skin is gone), and dug in, its jagged edges hold in the earth, its friction up to two and a half times. So a smooth rocket skates for a few tens of metres, and once its underside is torn (within metres, see below) it stops fast: the test rocket thrown at the grass at 70 m/s came to rest 60 to 80 m from where it first touched, 3 to 5 g (see What was tested). A round part rolling over soil is held back as a wheel in mud is, more as it sinks in.
• On paving, by friction that grows from a third of its weight for a smooth skin to nine tenths for a torn one, torn metal gouging, and a little more for speed. An engine (or any part with no skin to tear) is steel and all corners: seven tenths of its weight from the first, twelve tenths once it is broken, and it catches on the paving as it goes, the more the faster (0.35 m/s² for each metre a second it is doing: as set, by eye; see Limits for what plain friction would do). The friction acts where the engine touches and so turns it over; the catching is taken from its middle.
• A wreck that skips along is held back for the moments it is off the ground as well (since 0.2.2; up to three tenths of a second each): its weight comes down again each time as hard as the time it was up, and the ground's friction is owed on all of it, on paving and on soil; so is an engine's catching. Before, the drag acted only in the steps of the physics in which something happened to touch, and wreckage that skipped lost next to nothing: a pod lay 180 m from where it first touched, having touched the ground for 13 m of them. (Ploughing acts only while a part is in the earth.)
• A wreck that rolls or tumbles is held back as one that slides (since 0.2.2): where the place that touches is going slower than the wreck's middle, the drag is reckoned on the middle's speed and taken from it, and the wreck's turning is slowed by as much. Nothing of a wreck is a wheel: it comes down on its corners and edges at every turn, and each one catches (in soil, digs in). Over soil it ploughs a third as hard as one dragged through the earth does: it digs in at each turn and rolls out again (ploughing in full, the pieces of a rocket that had gone up were stopped dead, 25 m from where it first touched). A craft that is whole and rolls over soil is held back only as a wheel in mud is, as before.

Because the drag acts where the craft touches, below its middle, it turns the craft over that point: a long craft slews and, when one end digs in, cartwheels. "How far a wreck slides" divides it. Where the numbers come from is on the Research page.

The drag's work tears the skin that touches away from below. A share of it (a fortieth on soil, a thirty-third on paving) goes into the skin there: the plane below which the skin is torn away moves up into the part by as much as that work tears off (a square metre of a tank's skin takes some 11 kJ: by the weight of its structure a square metre, so that a capsule is no harder to grind than a tank of the same weight of metal). A panel half below the plane is torn off; one less below it is flattened up to it. So a tank sliding on its side loses the bottom of its skin within metres and keeps its top, and leaves shreds, flakes of paint and rivets behind it on the ground, and now and then a panel, folded up; with its underside gone it scoops the earth up (above), and what held it to the parts beside it there is gone with it, so that a long rocket comes apart into sections along its slide.

A part with no skin to tear is worn as a whole (since 0.2.2). An engine's bell, its pump and its mounting are whole meshes, and grinding from below takes none of them off an engine that tumbles (the plane it is ground to begins again each time it turns over). So a larger share of the drag's work wears the part itself (two fifths on paving, three tenths on soil, and as much of the ground's grip in each blow), counted against what crushing it right through would take. As the wear grows its meshes come away one after another, the one nearest the ground first, each a piece of its own, dented, with shreds and bolts; worn right through, the part goes altogether and its last pieces are left strewn where it was dragged, not sent on. A loose Swivel (1.5 t) thrown along the runway at 40 m/s lay 35 m on, a fifth of it gone; at 67 m/s, 60 to 78 m on, its mounting ring, its bell and its pipes strewn behind it and a half to four fifths of it gone (see What was tested). An engine crushed right through by a blow goes altogether too (until 0.2.2 one that had hit the ground at 54 m/s lay there whole).

The ground is marked. On soil, a scar: one for each wreck, as wide as all of it that touches the ground (measured across the way the wreck's middle goes, so that a wreck sliding sideways leaves a wide one): a shallow gouge that wanders and widens, beginning and ending in a point. Its floor is moist earth, darker than the ground's top, scored the way the wreck went, darkest under its edges where a trench's wall would be in shade. Its lips are low: a quarter as high as the scar is deep and nine centimetres at most, lumpy, gone altogether here and there, a sod turned over in them now and then. Beyond the lips the scar's picture is cut out (with the game's own cut-out shader): clods and crumbs thrown on the grass, fewer the further out, with the ground showing between them, so that the scar has no edge a ruler could have drawn. The rest of the earth is thrown: clods, and slabs of turf (grass on top, earth beneath) thrown aside at the scar's edges, which lie there a minute or more. A scar is never laid back along itself: the middle of what touches jumps about as a wreck's parts touch in turn, the length of the wreck and more, and a place behind the scar's end is ground already marked (laid back and forth, a scar lay in folds, one over another). A wreck that leaves the ground and comes down again further on leaves a scar in pieces. On paving a dark scrape; where steel drags (an engine, a heavy fitting) a stream of sparks, and chips and bolts of it (a tank's aluminium skin hardly sparks). The game's terrain is built afresh as the view moves, so it is not itself changed: these are meshes laid on it (a point every 0.4 m along a scar, behind a fast wreck as well, and thirteen across it), each point set on the ground beneath it, in the colour of the earth of the place (the picture is made again when the place is another world or another kind of country). A mesh cannot go below the ground's own surface (the ground would be drawn over it), so a scar's floor is drawn at the ground's level and its depth is in its shading, its lips and the wreck sitting down in it.

What the ground is (since 0.3.0)

Until 0.3.0 all ground that was not paving was soil. Now it is read from the world's own map of its biomes where the wreck is (what the game's science asks): on Kerbin its ice caps and tundra are snow, its deserts, badlands and shores sand, its mountains bare rock, the rest soil; the airless moons are dust (the Mun, Ike, Bop, Pol, Tylo, Dres); Minmus's flats ice and its slopes dust; Duna sand, with ice at its poles; Laythe's dunes and shores sand; Vall and Eeloo ice; Moho and Gilly rock. Each holds a wreck its own way, against soil's (or, for the hard ones, paving's):

Ground	Slides	Digs in	Throws	Scar
Soil	as before	to a quarter of its width	clods, slabs of turf, brown dust	dark moist earth
Sand	as soil, ploughs a third harder	half as deep again	pale dust, no clods	nearly as pale as the top
Snow	half as hard (a quarter of its weight)	2.4 times as deep, packing it down	lumps of snow, white powder	blue-grey in its own shade
Dust (the moons)	a tenth harder, ploughs a fifth harder	a fifth deeper	grey dust, no clods	a little darker than the top
Ice	as paving at three tenths of its grip: far	not at all	a little ice dust	scored white
Rock	as paving, three tenths harder, steel catching	not at all	sparks off steel, a little grit	a scrape, no crater

Where the figures come from is on the Research page. Seen at the open ground north of the runway with each kind given in its place (the development build's ground= test word): the test rocket thrown at 70 m/s, 4 degrees down, lay 48 m from where it first touched on soil and 73 m on snow, its scar grey-white and wider; on sand its engines and tanks lay 29 m on (its pod, thrown, further).

What becomes of a part

• A tank torn open leaks. Torn (any panel gone) or crushed in, it splits: what is in it comes out and pushes the craft the other way as it goes. Where there is oxygen in the air it catches three times in four; where there is none, only a tank that carries its own oxidiser burns, and then it does. Not alight, it runs out over some seconds and nothing goes up.
• What runs out stains the ground (since 0.3.0). Liquid fuel or oxidiser running out of a split (not a solid booster's, nor a gas) falls on the ground under the hole, if that is within 40 m, and spreads there as a spill does: to a film some 3 mm deep on paving, while soil soaks it up and is covered less widely, and as a dark, wet stain with a ragged edge. In the game (2026-10-18): an FL-T800's 4 t, split low on the test rocket on the launch pad, made a stain 26 m across on the pad's concrete (28 m is the most). Alight, it burns where it lies as a pool fire: 0.055 kg a square metre a second, as kerosene pool fires burn (31 kg a second there), its flame as tall as Heskestad's correlation has it (some 31 m for a pool 28 m across, 5 m for one 2 m across) under thick black smoke that climbs as a column, until the fuel is gone. Fuel on the ground turns it off.
• Alight, what is in it goes up a moment to a second and a half later (the worse the tear, the sooner): the game's own explosion where the tear is, made by Volumetric Explosions (where installed) from what was in the tank, told it was a crash and how fast. The skin near the tear is blown away as burning, blackened panels, and with them arcs of the tank's rings and bent stringers; the more there was in it, the more goes (from two thirds of the skin left for a few kilograms to a fifth for tonnes), the top of it, as it lies, kept longest; round the hole the skin is blackened and bent back in petals. The wreck burns on where it went up and goes on burning as it slides (see below).
• A split solid booster burns through the split, white, and when it breaks up most of its propellant goes with its pieces, burning, rather than into the blast.
• A hurt part bends before it breaks: what holds it to the part it hangs from is softened as it is hurt and as the skin there is torn away, down to a twelfth of its stiffness, so that it sags and folds.
• Torn through, it comes apart: skin no longer joined, through panels still on, to the rest of the piece of skin it was part of comes away as one piece (a tank torn right round comes away in two). A part that has lost the skin where it is joined to the part beside it comes away from it, with whatever hangs from it, and carries on as a craft of its own. Coming apart where parts are joined is otherwise rare: what breaks is the part's own skin.
• Almost nothing left (less than a sixth of its skin; an engine, worn or crushed right through), a part goes altogether: what is left of it in pieces, and its explosion if it still carried anything that burns. A part with nothing in it that burns is crushed, not blown up: dust and sparks, and no fireball.
• A part that is hurt before its skin is cut (a craft that hit within a fraction of a second of being armed), or whose meshes cannot be read, breaks up the old way: when hurt past whole, its skin is cut there and then into a few pieces and it goes.

Cabins (since 0.5.0)

Asked for on 2026-10-25: "make it so that the cockpit where the Kerbals reside can blow up and fragment too". Until then a cockpit or pod came out of nearly every crash whole, its crew alive, the rest of the craft in pieces round it, for two reasons:

• What a part takes before it is crushed through goes as the square of its crash tolerance (see A blow), and the game's tolerances for cabins are gameplay numbers: 14 to 20 m/s for the capsules (so that one survives a hard landing on land), 40 to 50 m/s for the aeroplanes' cockpits and cabins (so that a hard landing on the runway does not lose the crew), where a tank has 6. The Mk1 Cockpit took 35,000 kJ to crush through, an FL-T400 tank 160: 8 to 13 times what a capsule of the cockpit's weight takes. So a cabin's structure is now reckoned at no more than a capsule's tolerance, 14 m/s (the Mk1 pod's own), for what it takes, what is only a touch, and what a slide along the ground does to it. The Mk1 pod is as it was; the Mk1-3 pod and every cockpit are weaker, as a capsule of their weight.
• Nothing tied the crew's life to their cabin. The game kills a crew only with their part (Part.Die: each of them dies, and where the game is so set a new one comes in their place after a while), and this mod let a part go only once less than a sixth of its skin was left: the test rocket's Mk1 pod, crushed in and slid 100 m on its side down the runway, its monopropellant gone up in it, lay with 28 % of its shell left and Bill sitting in it unhurt. Now a crewed cabin broken open goes to pieces, and its crew with it, the game's own way: crushed in by a quarter of its length, or with less than three fifths of its shell left (torn off, ground away, blown off), or with its own propellant gone up in it (a burst inside the cabin: the split monopropellant tank that every pod and cockpit carries leaks and, in air, catches three times in four, as a tank does). It goes as a tank does: what is left of its skin in pieces, hot and burning where it burst, and its explosion if anything that burns is left in it. The log says who died with it.

A cabin with nobody in it is only weaker (it tears as any part does). A cabin that is dented, scraped or holed a little keeps its crew: a pod slid down the runway on its side at 78 m/s, its leak not alight, kept four fifths of its shell and its kerbal. Cabins break up too (on as installed) turns both off: a cabin as strong as the game makes it, its crew alive while any of it is left.

With Smooth Portraits 0.3.0, a kerbal killed so has their last moments in their portrait (what the cabin's camera saw: the blow, the flash and the fire's light, the picture breaking up and the feed lost).

The pieces

• Panels: each panel torn off becomes a piece made of its own triangles, with the inside of the skin and its torn edges, as thick as the wall, all round it; bent about a line across it and crumpled by how it was torn (ground away and crushed panels most, a piece torn right off whole least), blackened where it burned, dirtied where it was ground. An engine's bell and its machinery come away whole, dented rather than folded.
• Bits: with every panel, shreds of skin, flakes of paint and rivets (and from a spacecraft's skin, shreds of its foil blanket): too many and too small to be pieces each with a body of its own, they are moved by the mod, fall, bounce once or twice off the ground and stop, and stay a minute or so (those lying still cost next to nothing). A part takes two milliseconds at most making pieces (four when it goes altogether) and always makes one; what more comes off it then is bits only, and so is more of it when the frames are already slow. What can wait shares one budget a frame (eight milliseconds of this mod's work in the frame's physics steps): past it, what was torn off is made into pieces in the next frames, where the part has got to by then, and so are a burst tank's rings and stringers, the parts going altogether, a torn part's letting go of the parts beside it, and split tanks going up; at least one of each kind is done every frame (one part going or let go, taking turns: each splits the craft, the game's own heavy work), so nothing waits long. Until 2026-10-24 each physics step had budgets of its own and did at least one of each whatever it had spent, and a frame of two steps took up to 70 ms of this mod's on the PC; a part going costs the game itself 5 to 18 ms (its own destroying, the craft it splits into, every mod hearing of it). On the PC's release builds a crash's worst frame came down from 52-122 ms to 56-70 (three crashes each). And while a craft that may crash is watched, one untouched part's skin a frame is drawn ahead, hidden, the part drawn by its own as ever: a part's first drawing is the most work its skin takes (3 to 12 ms of a crash's frame on the PC), and at the first blow only what was struck is drawn again (1 to 3 ms); the skins drawn ahead are let go again if the craft comes through untouched.
• Rings and stringers from a torn tank (one whose skin is round about its long axis): arcs of its frames and bent bars, bare metal.
• Each piece is a solid body with its share of the part's mass, a collider round it (the convex hull of a big piece, a box round a small one), and the speed that point of the part had, thrown as what tore it off would throw it: what the ground tore off is left behind, what a blow crushed is thrown out from the part, what a burst blew off is thrown out from the burst. What was going into the ground is sprayed out along it.
• They are the game's own kind of loose object (as a fairing's panels are once cast off), so the game moves them with everything else when it shifts the world about. The air's drag on them is the mod's own (a tumbling plate, by its area); their weight is the game's while the craft being flown is whole, the mod's after.
• For their first third of a second they are on a layer of the physics that hits the ground and nothing else, so that pieces of one part do not throw each other apart at once.
• A piece that has lain still for a second and a half is left lying, out of the physics, until a blast sets it moving again. There are at most so many ("Pieces at most", 150 as installed): when there are more, the oldest go, those lying still first, sinking into the ground as they shrink. Each goes after "How long pieces stay" (two minutes as installed) anyway. A piece that goes is kept, hidden, for the next one to use.

Wrecks moving further off (since 0.4.0)

The game puts a craft on the ground or the sea on rails, frozen where it is, once it is 350 m from the craft being flown (2.25 km in the air): a wreck still sliding there, or a piece still tumbling, stopped dead mid-slide. Physics Range Extender widens every craft's ranges for that, with known faults where craft far off on the ground are thrown about as the game moves its frame under a fast craft. Here only the wrecks a crash is watching get the air's 2.25 km on the ground and the sea too, each craft's own ranges and not the game's, and only while it is watched: once a wreck is left as it lies, its ranges are given back as the game had them, and while the craft flown goes faster than 250 m/s every wreck has the game's own. A setting, "Wrecks moving further off", on as installed.

Tried (2026-10-24, the Mac): the test rocket thrown at the grass east of the pad at 250 m/s: pieces 443 and 488 m from the craft flown slid on at 1.0 and 0.8 m/s in physics where the game would have frozen them; each, come to rest, was given the game's 350 m back and put on rails (DEV Fragmentation.Tests.Ranges).

Kept in the save (since 0.3.0)

What a crash leaves is written into the game's own save (a scenario of the mod's, Kept), so that a quicksave and a quickload, or leaving the flight and coming back to it, find the wreck as it was:

• the marks on the ground: each scar's and scrape's points along it (where, which way across and up, how wide and deep, how far along), each crater's place, turn, size and slant, each fuel stain's place, what was spilt and burnt, and whether it burns; laid again on loading once the ground under them is there (the world's ground is built over the first seconds of a scene);
• the torn skin of every part still there: which panels are gone and which are burnt, where it was crushed and dented and how far, which panels are bent back and how, how far it has dug into the ground; done again on loading once the part is near and its shape is cut, nothing thrown (what was thrown is gone).

The loose pieces and bits are not kept: they go when the flight is left, as they go in time anyway. In the game (2026-10-19, the development build's own keep and lay-again, the game's save being the released mod's): two scars, a fuel stain and the test rocket's FL-T400 torn open (41 panels gone) written in 17 KB; the marks taken away and the tank mended, then all of it read back: the scars and the stain where they were, the tank torn as it was.

With Volumetric Explosions

The explosions come from the game's own, as always. Through the ways in the explosions mod has for other mods, this mod says once a frame what else is burning or rising:

• Every piece trails a little smoke: a wisp for a few seconds off one torn out of the ground or crushed, smoke for longer off one that came out of a fire, flame and smoke off one that burns; and so do the bits that came out of a fire, and a hundred of the others. These go through the way in added for this mod (Trails): each is laid as puffs straight into the patch of air it is in or near, and never begins a patch of its own (beginning one is the dear part of the explosions mod's work; see What was tested).
• The wreck's fire goes with it: after a tank has gone up, the wreck burns where it went up and goes on burning as it slides, dying down over twenty seconds or so: puffs of flame and black smoke laid where the burning part is, frame by frame, into the air it is in (the same way in as the pieces' smoke), so that its smoke streams out behind it along its way. Each leak likewise: white vapour, or flame and black smoke where it caught; fire alone in a vacuum. (The explosions mod can also draw a fire as an engine's flame, in a patch of air of its own going along with the craft; this mod asks for that only in its development build: each such patch is worked out and drawn every frame. Measured again on 2026-10-10 with Volumetric Explosions 0.6.0: the same crash ran at 28 and 33 frames a second in its first two seconds with them, against 41 and 45 without; see What was tested. Asked so, it says what each is: a burning leak a jet, a wreck on fire something burning with no jet, whose smoke rises off it as a plume.)
• The dust and earth a craft throws up sliding over soil: brown, in the patch of air it is in.
• A tank that goes up and stays is noted to the explosions mod as a part that died would be, with what was in it, through the way in added for this mod (Records.Burst), so that its blast is made from what was in it although the tank itself is still there.

The explosions mod's smoke goes round the bigger pieces as they fly (Movers), and round craft.

With Smooth Running

The bits go with the game's moving frame, as the craft do, and are moved every frame. Where Smooth Running carries the craft on between the game's physics steps, the bits are carried on with that frame, all at once, by their root (Keystone.Motion.RideWithFrame); their particles are kept in that root's own space for it. The pieces are loose bodies of the game's own kind, which Smooth Running carries itself (2026-10-18).