Keplerian Drift

Thrust fires engines whose nozzles face aft. Retro fires engines facing the nose.

Turn spins the ship with its gyros. Side thrusters join in pairs: RCS pods or side-facing engines (any mix) ahead of the center of mass push one way and those behind it the other, throttled so the ship turns without sliding. A side engine with no partner still helps, shoving the ship sideways as it does; a lone pod at one end doesn't. With a flight computer aboard and ASSIST on, the pairs also fire the other way when you let go of TURN, stopping the spin faster (the TURN button glows). Pods burn fuel for this; gyros don't. Let go and the gyros stop the spin and hold your heading, against lopsided thrust and knocks too, as far as their torque allows. A ship with no gyro can only turn with side engines, and won't hold a heading at all. The cockpit is only where you sit: it has no gyro or computer of its own.

Engines take time to spool up: a rocket needs 0.7 s to reach full thrust and a torch 1.4 s, and each takes a little under half that to wind down. Ion drives are slowest of all, 3 s, because they have to warm up (real ones take minutes), but they cut out instantly. The ring around the THRUST and RETRO buttons shows how far they've spooled.

Slide pushes the ship sideways without turning it. It uses RCS pods and any engines mounted to push sideways. RCS responds instantly but is weak, burns main fuel fast, and overheats after about 2.5 s of continuous firing; the ring around the SLIDE buttons shows its heat. Sideways rockets push harder but need time to spool, so start big slides early. With assist on, the flight computer throttles back any side thruster whose spin the gyros can't cancel.

Assist is the Flight computer modules you fit; with none fitted there's no ASSIST button. It never steers and never slides you. It does two jobs, only with your own hardware and only on controls you aren't touching. Brake assist: when the guide line ahead is turning red, it eases off THRUST and fires RETRO. Spin stop: when you let go of TURN, it fires your side-thruster pairs (RCS pods or side engines ahead of and behind the center of mass) against the spin, on top of the gyros, so the ship stops where you aimed it. More modules brake earlier and catch smaller spins. Braking needs a retro engine and spin stop needs side-thruster pairs; both burn fuel. The buttons it's working glow cyan, and THRUST goes dashed while it's holding it back. The ASSIST button shows how many modules you carry (●●○) and switches them off. Each module weighs 0.5 t and is fragile.

Gates and pylons: fly through a gate between its two posts, in the direction of its chevrons. A pylon is a single post you pass on one side: the curved arrow round it shows which side and which way, and the short red dashed bar marks the side that doesn't count. Pass on the wrong side and you have to go back round. Pylons are solid, so don't clip them.

Dust traps: an arc of thick stardust lies on the outside of the turn at every pylon, like the gravel beside a racetrack's hairpin, at least 40 m clear of the racing line. Run wide and you plough into it: it takes about a third of your speed off, so you can still turn back to the pylon instead of sailing off into the boundary.

Refuel areas: every checkpoint has one, marked in blue. The start/finish line has a box 100 m long running back from the line, every other gate a strip 50 m long before it (both on the approach side only), and every pylon a whole circle 40 m round its post (the course passes 30 m from the post, through the outer part of the circle; fly closer or stop beside the post to fill up). Any ship inside one takes on fuel at 0.05 t/s for as long as it stays, whatever its speed and whatever the size of its tanks, so a ship with big tanks takes longer to fill up. Flying through a gate strip at 40 m/s gives you about 60 kg; stopping fills your tanks while the clock runs. While you're refuelling the fuel bar glows blue, and a striped segment at the end of it shows what the next ten seconds will add. So a light ship with few tanks can race and stop to refill wherever it runs low, and the rivals stop too when they're running short.

Tracks run from easy to hard. Pylon Sprint is just pylons and a crosswind; Nebula Drift adds dust clouds to scoop or skirt and a small black hole; Kessler Loop throws in everything; Slingshot is a long loop round a huge black hole. Demo (next to Launch) lets a computer pilot fly your own ship round the selected track, alone, so you can watch the line it takes, where it brakes and how it uses the guide line; the buttons it presses light up. Demo times don't count as your best.

Guide line: the trail of colored dots ahead of you is the ideal path through the next gates, planned for your ship's own thrust and braking. Its color compares it with your current speed: green, you could go faster; yellow, hold it; red, you're too fast for the bend ahead and need to slow down now. Red dots are also bigger. When you're well off the line, a faint dotted lead runs from your ship to where you'd rejoin it. Switch it off from the pause menu, or with G.

Pilot hints: what the demo pilot would do in your place, shown but never done for you. A chevron on a ring round your ship marks where your nose should point; a dashed arc from your nose shows which way to turn. Once you're lined up it turns orange with THRUST when it's time to burn, red with RETRO when it's time to brake on your retro engines, and stays a faint outline when the right thing is to coast. The buttons she'd be pressing get a dashed outline. A red BRAKE bar across the guide line marks where you need to start braking for the bend ahead at the speed you're doing now (for a ship without RETRO it allows the time to swing round tail-first). She paces herself by your fuel gauge, and when your fuel won't last the race she'll point you into a refuel area and show STOP, then REFUEL. Switch hints off from the pause menu, or with H.

Course boundary: stray more than about 250 m from the course and you fly into dark boundary dust that thickens the further out you go, until it stops you dead. When you're deep in it, stalled outside the course, or out of fuel, a RETURN button appears: one tap tows you back to the last gate for 10 s.

Open space has no friction. You drift until you burn the other way. The dotted line ahead of the ship is your coasting path, bent by gravity and dust.

Black holes pull with the inverse square of distance. Dashed rings mark where the pull reaches 2 and 8 m/s². Touch the black disk and the run is over. Very close in, the pull on one end of the ship is much stronger than on the other, and those tides tear parts off. Shields don't help.

Dust drags on every exposed cell like air. A narrow nose and a heavy ship lose less speed. A dust scoop turns that dust into fuel while you fly through nose-first, at the price of extra drag.

Solar wind streams (pale gold streaks) are fast-moving gas that presses on whichever side faces it. Ride one going your way and it pushes you until you match its speed; go faster than it and it turns into a headwind; cross one and it blows you sideways. Wide ships catch more of it.

Gates are one-way. The chevrons on each gate point the way it counts; crossing it backwards doesn't count, and you have to come back through it the right way.

Frames are the skeleton: they link to each other and to the cockpit, and every other part must sit on a frame or next to one. A cell can hold a frame with one part bolted on top. Light trusses save mass; heavy girders survive hard hits.

Rocks orbit the big black hole. Impacts trade momentum, spin you, and damage the part that hits; shields soak damage first. 40% of what gets through travels into the frame that part sits on (or the frames beside it), so a truss can snap even when the hit lands on the part bolted to it. Any part that loses its link to the cockpit floats away. Armor plate is the exception: it takes 12 off every blow (rocks, weapons and missile blasts alike) before it's damaged at all, and none of the blow reaches the frame under it.

Track builder: build your own tracks. Pick ＋ Build a new track… at the end of the Track list, or open any track's MAP and tap COPY to start from a copy of it (EDIT for one of your own). Choose a tool along the bottom (Gate, Pylon, Hole, Dust, Wind, Rocks, UFO) and tap the map to place it; checkpoints are flown in number order from the start/finish gate F, and a new one goes after the checkpoint you have selected, or last. In Move, tap something to select it, drag it to move it, and drag its white handles to turn it (↻) or size it (↔); the panel underneath sets the rest: gate width, which side to pass a pylon, a black hole's pull and its ring of rocks, wind speed, dust thickness, and the order of checkpoints. The guide line redraws as you go and turns red where a black hole forces it out wide. ↶ undoes, ⤢ fits the track to the screen, ☰ saves, opens, exports to a file, copies as text and imports, and RACE saves it and races it (or lets the demo pilot fly it). Your tracks are kept in this browser and appear in the Track list as Custom; export them to move them to another browser or share them.

Track map: tap MAP beside the track picker (or the radar during a race, which pauses it, or Track map in the pause menu) to see the whole course north-up. Drag to move round it; pinch, scroll or double-tap to zoom. It shows every gate and pylon with its number and which side to pass, the refuel areas, dust and dust traps, solar wind, black holes with their 2 and 8 m/s² rings, rocks, UFO zones, and the guide line with arrows for the way the course runs. In a race it also shows every ship, and colors the guide line by how fast your ship can take it (green fast, red slow).

Tap VIEW (top right) to choose what points up the screen: your ship's nose (the default), your direction of travel, or north. The radar map in the corner turns with the view and keeps your ship at its center. It shows 600 m around you; the N on its rim marks north, and an orange pip on the rim points to the next gate when it's out of range.

The camera reacts only to acceleration you'd feel. Thrust and the ship surges ahead; brake, plough into dust or hit a rock and it drops back, in proportion to the push, then settles back within about a second once the push ends. At any steady speed, and in pure free fall around a black hole, the ship stays at its usual spot on screen. The faster you go, the further the camera pulls back (from 100 m across the screen at rest to about 420 m flat out), but ships are drawn larger than life, so they stay easy to see: against the course they look about one and a half to two times their real size. Collisions still happen at the real hull, so a rock can seem to clip you and fly past.

Cruise: forward engines on the cruise group (ion drives by default) run while the CRUISE switch above THRUST is on, and keep running until you switch it off, so you pay their warm-up once. THRUST fires the main group. Both can run together. Change an engine's group in the garage by tapping it.

Laser: press FIRE (or Space) to shoot where the laser points; aim by turning the ship. Each shot costs a little fuel. No recoil.

A rock's strength is its size: hits erode it, so it visibly shrinks. A big rock (14 m across or more) breaks into two equal pieces once it is down to half its strength; the pieces share what is left and drift apart, which often opens a gap. Clearing a rock completely always costs exactly the strength it started with.

Turret: automatic and never runs out, but weak. It faces your direction of travel, picks the rock most likely to hit you, leads its shot, and keeps firing. Alone it clears small rocks and can break medium ones on a slow approach; big rocks need several turrets working together. Each round kicks the ship back the other way, and it can't shoot through your own hull.

The small diagram beside your gauges is your ship: each part's outline shows its health (green, yellow, red), tanks show fuel, engines glow when firing, RCS shows heat, lasers show charge, turrets light up while engaging a rock, the blue outline is your shield, and dashed red squares are parts you've lost.

Sound: tap SOUND to switch between music and effects, effects only, or off. Each difficulty has its own race music: bright and bouncy on Easy tracks (and free flight), driving on Medium, dark and fast on Hard and Expert. Engines rumble louder and brighter as they spool, ion drives whine up as they warm, and a low drone grows near black holes.

Boost: a boost cartridge holds two single-use bottles. Tap BOOST and one empties over 3 s into your chem rockets and torches for up to 60% more thrust, burning its own propellant at a poor exhaust velocity, not your main fuel. Forward rockets light by themselves for the boost but still need their spool-up time, so boost early. One bottle feeds about 150 kN of rockets at the full 60%; bigger engine clusters share it. Ion drives can't use it.

Missiles: tap ARM above THRUST and wait about a second while it arms, then tap any rock to launch at it. The pod facing that way fires. You can tap a UFO or a ship too. Missiles are slow on purpose: 3 s of rocket fuel adds about 60 m/s to the speed you launched at while it steers itself onto the target (it aims where the target is going, not where it is), then it coasts, and after 10 s it blows itself up. So gravity bends a long shot, a rock in its path sets it off early, and a quick ship that sees one coming from 300 m and floors it straight ahead can outrun it. Turrets shoot down missiles aimed at their ship, if the hull isn't in the way (a turret on the nose can't see one coming up behind), and so can a laser. The warhead only arms 25 m clear of your ship and its blast reaches 20 m, so don't fire at a rock you're about to hit. One hit destroys most rocks and breaks the biggest in two.

Mines: tap MINE (it shows when you carry a Mine layer) and one drops out of the back; a small charge brakes it to a near stop, so it stays about where you dropped it, then it drifts like a rock. Its light blinks once it's armed (30 m from you; until then it's safe, and a shot only breaks it up) and a faint ring shows how far the blast reaches. It goes off on touching anything, your own ship included when you come round again, and it hits hulls more than twice as hard as a missile. A laser or turret round sets one off from a distance, and turrets fire at one in your path by themselves. Rivals see them and steer round, the clumsy ones not always in time. A mine that catches a ship counts as an attack by whoever dropped it. Mines go inert after 90 s.

Rivals fly the same physics with the same controls you have. Pick up to five. VEGA is calm and the best pilot. LARK is calm and middling. MOTH is calm, slow and clumsy. VIPER is territorial, a middling pilot, and armed with a laser and missiles. WASP is territorial too, a poor pilot with a laser and armor plates. With 1 to 5 rivals you race them in that order: VEGA, VIPER, MOTH, LARK, WASP. Aggression sets how many of them are territorial: Med (the default) is VIPER and WASP; Low leaves only VIPER; High adds LARK and MOTH; All makes everyone territorial; None makes everyone calm (VIPER and WASP keep their guns but only shoot back). With fewer rivals it's roughly the same share. A rival made territorial that has no gun fits a laser on its nose for the race: VEGA in place of its scoop, MOTH in place of its turret, LARK as an extra 1.2 t. Their name tags turn red with an ✕ once they're at war with you, and the HUD shows your place (P2/4). When a rival is off screen, an arrow in its color at the edge of the screen points at it, with its name and distance: the closer it is, the bigger the arrow.

The start: everyone lines up side by side across the start line, and until you cross it you can only go straight at it (THRUST, CRUISE and BOOST work; turning, sliding, RETRO and firing don't), so the grid can't swerve into each other. Your side thrusters, if you have any, hold you in your lane against any pull to the side. It lifts once you're past the line, or 20 s after GO.

Multiplayer: up to six ships on one WiFi network. One device hosts (a laptop is best; it can race or just watch, and add computer rivals to fill the grid); the others tap MULTIPLAYER, Join a game, and type its room code. Everyone races the ship in their own bay. Your own ship is flown by your own device, so it answers at once; the others are drawn from the host's reports. There's no pause and no time warp in multiplayer. Linking up needs an internet connection (the free PeerJS server); after that the race runs over your WiFi.

Who fights whom: rivals start out friendly, so your turret leaves them alone. A ship that hits you with a weapon, launches a missile at you or catches you with one of its mines becomes your enemy (a stray turret round meant for a rock doesn't count): your turret engages it and it shows red. It works the other way too: shoot a calm rival and it fights back. A territorial rival (VIPER and WASP, unless you change Aggression) guards its space: fly inside the red ring around it (70 m) and it turns its laser on you, and on any rival that does the same, until you back off past 110 m. The ring only counts once it's past its first checkpoint, so the scramble off the start is left alone. A ship out in front of it doesn't count (it's the one catching up, or it's pulling away), and refuel areas are neutral ground: it holds fire while either of you is in one. Shoot it first and it comes after you at any range, missiles included. Fights burn out: 15 s after whoever started it last landed a hit, both sides go back to leaving each other alone (shooting back doesn't keep it going). Bumping into each other is never counted as an attack. Turrets hold fire when a ship they aren't fighting is in the line of fire.

UFO zones (dashed green rings) launch saucers when a ship comes near. They hover in your path and lob slow globs of goo: 350 kg each, so running into one is an inelastic collision that costs speed, and the goo stays stuck to you, making the ship heavier, until it boils off after about 7 s. A glob also does a little damage. Lasers, turrets and missiles all bring UFOs down, and turrets shoot down globs headed for you, and incoming missiles too.

Weapons hurt hulls less than rocks: a laser shot takes 220 strength off a rock but 40 HP off a hull part, a turret round 10 versus 2.5, and a missile blast up to 20 HP for every exposed part within 20 m, after the shield has soaked what it can (a UFO caught in one takes up to 150).

Keyboard: arrows or WASD, Q and E to slide, Space to fire, C for cruise, F for assist, B to boost, M to arm missiles (then click a target), X to drop a mine, T for time warp, R to tow, G and H for the guide line and hints, V for view, Esc to pause.

Keplerian Drift

Parts

Spec sheet

How to play

Learn by flying

Build it. Fly it. Race it.

Nothing slows you down

Left thumb steers, right thumb pushes

Checkpoints, in order, every lap

What's out there

Every part has a job and a weight

Parts break, one at a time

Five pilots, five tempers

Straight to the line

Up to six ships on one WiFi

Start gentle

The details

Keplerian Drift