Colours: ■ cold liquid CH₄ ■ warm supercritical CH₄ ■ LOX ■ fuel-rich hot gas
The methane side of Raptor 3, station by station: how liquid methane at a few bar becomes 950 K gas at 800 bar, spins a 47 MW turbine, and powers the very pump that feeds it. Click any part or numbered station to see its pressure, temperature and flow.
All gas moves one way: pump → cooling jacket → preburner → turbine → main chamber. The "loop" is the shaft: the turbine hands its power straight to the pump it shares a shaft with. The other loop is heat, carried from the chamber wall back upstream by the coolant.
No gearbox, generator or hydraulics hang off this shaft as far as anything published shows. Raptor's steering actuators are electric, powered by the vehicle.
About 94% does. Roughly 10 kg/s is tapped off to heat the oxygen-rich preburner on the other side. And methane doesn't go straight from the pump to the preburner: it cools the chamber first.
That figure comes from the early 650 kg/s total. At Raptor 3's 250 tf and ~327 s Isp the engine swallows ~765 kg/s, so methane is ~166 kg/s.
Flattened for clarity: the real turbopump is a compact vertical unit with the preburner welded directly onto the turbine inlet. Line colour shows the fluid; line thickness is fixed, not flow.
Methane is pushed up to the highest pressure anywhere in the engine, then spends it in stages. Each drop is a deliberate price: cooling, injector stiffness, and above all the turbine. What's left has to stay above 330 bar so the gas can still flow into the chamber.
Each dot is a station; each arrow is one step, coloured and labelled by where the energy for that change comes from. Pressure uses a log scale so the 4 bar inlet and the 950 bar discharge both fit. The main chamber, at ~3,600 K, is off the right edge.
Pressure only ever rises in one place, the pump, and that energy is shaft work from the turbine. Temperature rises in three places: pump losses (small), chamber-wall heat in the cooling jacket, and burning in the preburner. Every other step spends pressure, either to friction or, in the turbine, on purpose.
Warm, supercritical methane (156 kg/s) and liquid oxygen (36 kg/s) meet in a small, thick-walled chamber at about 800 bar. That is an oxygen-to-fuel ratio of only ~0.23, against 3.6 in the main chamber and ~4 for complete burning.
The oxygen runs out almost immediately. Only about 6% of the methane actually burns; the remaining 94% is just heated by it. The mixture leaves at roughly 950 K, hot enough to carry a lot of energy and cool enough for turbine blades. The outlet temperature is set almost entirely by how much oxygen the FPOV lets in.
A torch igniter (a small spark-lit methane/oxygen flame) lights it at startup. Once running it is self-sustaining. Musk has said the preburners run at 700 to 800+ bar Published, which matches what the power balance on this page needs.
The most likely layout (not published) is a single-stage axial turbine Estimate. Full-flow is the reason one stage is enough: because nearly 200 kg/s goes through it, each kilogram only has to give up ~247 kJ, a pressure ratio of about 2. Gas-generator engines starve their turbines of flow and need high ratios and often two stages.
Stage 1a, nozzle guide vanes (stator): fixed, curved vanes that act like nozzles. Almost all the pressure drop happens here, 795 → ~390 bar, turning pressure into a jet at roughly 700 m/s aimed sideways at the rotor.
Stage 1b, rotor blades: curved buckets on a disk welded to the shaft. The jet slams in and is turned back the other way; reversing its direction pushes the blades round. Gas leaves slow, at ~385 bar and ~880 K. Blade count isn't published; turbines of this size typically carry 40–80 blades per row.
Methane is light: ~440 kg/m³, under half the density of LOX. Pushing it from 4 bar to ~950 bar means a head of about 22 km, as if lifting the liquid 22 kilometres straight up. One impeller can only add so much before its tip speed gets dangerous (~600 m/s), so the job is most likely split across two centrifugal stages Estimate.
Inducer. A screw-like axial rotor at the inlet. It gently raises pressure by a few tens of bar so the impeller's low-pressure zones don't make the methane boil locally (cavitation), which would destroy the pump. Raptor has no separate boost pump; the inducer does that job, helped by subcooled propellant.
Impellers 1 and 2. Each flings the liquid outward, adding roughly 470 bar. A crossover passage leads from the first to the second.
Volute. A spiral casing that slows the liquid and converts its speed into pressure before the discharge duct.
Bearings and seals. Cooled and lubricated by methane itself. A full-flow bonus: the turbine gas is fuel-rich and the pump fluid is fuel, so a leak across the seal is harmless. Single-preburner engines need a helium-purged barrier seal between oxygen and fuel on the same shaft.
| Shaft figure | Value | |
|---|---|---|
| Pump hydraulic power | ~36 MW | Estimate |
| Pump losses (heat into CH₄) | ~11 MW | Estimate |
| Turbine shaft power | ~47 MW | Estimate |
| Shaft speed | ~30–40k rpm | Estimate |
| Torque at 35k rpm | ~13 kN·m | Estimate |
| Pump efficiency assumed | 77% | Estimate |
| Turbine efficiency assumed | 80% | Estimate |
For scale: 47 MW is roughly the output of a large ship's main engine, on a shaft you could hold in two hands. SpaceX's 2016 estimate was ~80 MW for both turbopumps of a larger, 300-bar Raptor Published.
This is the honest version of "energy flowing backward". Two quantities recirculate: shaft power (turbine → pump, mechanically) and heat (chamber wall → incoming methane, through the coolant). Both end up back in the main chamber; nothing is thrown away.
The exhaust jet carries ~3.9 GW. The whole methane turbopump runs on about 1.2% of that, which is why a small preburner can drive it.
How the estimates were made: start from the published thrust, chamber pressure, mixture ratio and sea-level Isp; assume typical pump (77%) and turbine (80%) efficiencies, an ~80 bar cooling-jacket drop, an 8% preburner injector drop and a 15% main injector drop; pick a 950 K turbine inlet; then solve for the pump discharge pressure at which turbine power exactly equals pump power. The result, ~800 bar in the preburner, lands inside the 700–800+ bar range Musk has quoted, which is a useful cross-check. Real Raptor values will differ.