A throttleable rocket engine built on a lathe, flown from 100 m away
Gaseous oxygen and ethanol meet at a brass pintle inside a graphite liner. Every valve is driven by the pad computer, every step is gated by a measurement, and the whole stand carries over to the lander.
Same engine, tank and valves in both phases. Only the oxygen regulator and the pintle tip change.
Fire it from the control table
Arm the stand, fire, and drag the throttle during the burn. Flow animates in each line, closed valves turn solid, and the sequencer aborts on its own when a check fails. Click any component in the schematic for a picture and what it does, or inject a fault to watch the safety logic work. The model is simplified, with the numbers from the design point.
Eleven parts, all lathe work
Drag to orbit, scroll or pinch to zoom. Pick a part on the model or in the list and the camera flies to it. The exploded view follows the assembly order, so every part leaves the way it goes in; Play assembly puts it back together step by step. Dimensions follow the 400 N design, and the SolidWorks models can replace these shapes later.
Why it is built this way
Every material here is something the team can buy and machine today: 6063 aluminium, brass, stainless, graphite and copper refrigeration tube. Each choice below follows from that.
Chamber pressure is set by the regulator
At 15 bar the 6063 sleeve sees about 10 MPa of hoop stress, under a tenth of its yield. The real limit is the oxygen regulator: the venturi needs about 25% more pressure upstream than the injector, and the valves take 2 to 3 bar more. Phase one runs a 15 bar regulator at 9.5 bar chamber pressure; phase two adds a 24 bar regulator for the full 15 bar.
A graphite liner takes the flame
The gas is near 2,900 K. Aluminium melts at 660 °C and burns in oxygen, so a bare 6063 chamber would fail in the first second. One piece of graphite forms the chamber, throat and nozzle, and it slides out for inspection after every firing.
Ceramic paper keeps the sleeve cool
Graphite heats through in about 2 s. Three millimetres of ceramic paper slows the heat into the sleeve, centres the brittle liner and absorbs the difference in expansion: aluminium grows about six times more per degree than graphite.
The sonic venturi is the flowmeter
While the gas in its throat is at the speed of sound, oxygen flow depends only on the inlet pressure and temperature. One transducer and one thermocouple make it a flowmeter, and the choked throat stops chamber pressure swings from travelling back up the line.
Two throttle actuators, on purpose
Oxygen is throttled by a 1/2 in ball valve on a 150 kg·cm servo, because no small needle valve passes 290 Nm³/h. Ethanol is throttled by a needle valve on a NEMA 17 stepper, which gives fine steps on the liquid side. Flying one of each shows which actuator the lander should use.
Tie rods with disc springs
Four M8 A2-70 rods clamp the head, sleeve and retainer plate. Heat cycles loosen nuts more than vibration does, so disc springs keep the clamp load steady as parts grow, all-metal lock nuts sit at the hot end, and paint stripes show any movement.
It fails safe without software
Cutting power is always the safe move. The E-stop loop drops solenoid power through a relay: main valves close and nitrogen purges open, with no code involved. High-pressure oxygen is only ever opened by hand.
| Device | With power lost | Why |
|---|---|---|
| SV-1, SV-2 main valves | Close | Normally-closed solenoids stop both propellants |
| SV-3, SV-4 igniter | Close | No torch gas without a command |
| PV-1, PV-2 purges | Open | Normally-open solenoids flush both manifolds with nitrogen |
| RV-1, RV-2 reliefs | Open at 30 bar | Spring-loaded, no power needed |
| CV-1 to CV-4 | Block backflow | Fuel cannot reach the oxygen side, or the reverse |
| Automatic abort when | Check |
|---|---|
| No torch flame 0.3 s after the spark | TC-5 |
| Chamber below a third of full pressure 0.3 s after fuel opens | PT-5 |
| Chamber pressure off its setpoint by more than 20% | PT-5 |
| Sleeve above 120 °C | TC-1 |
| Venturi no longer choked | PT-1, PT-2 |
| Fuel tank pressure dropping toward the chamber | PT-3 |
| Telemetry link lost for 200 ms, or E-stop | Hardware |
Twelve gates before the showcase firing
Each step has a written procedure and a go/no-go, and the next starts only after the one before it passed. Nitrogen stands in for oxygen in every cold flow. Hot steps need the mentor present.
- Clean and leak-checkOxygen-clean the GOX side, leak-check everything with nitrogen at 25 bar
- Hydrostatic proofFuel tank and engine with the throat plugged, water at 45 bar
- Electronics bench testEvery abort path, E-stop, power loss and link loss, with no gas
- Fuel cold flowWater through the injector: flow against pressure drop, spray on camera
- Oxygen-side cold flowNitrogen through the venturi and annulus, then both sides together
- Throttle mappingMap both throttle valves and tune the control loops on cold flows
- Igniter aloneAt least 20 lights, timing command to flame
- Ignition pops0.5 s, then 1 s at 60% flow
- Short firings3 s and 5 s at full flow, throat measured after each
- Steady 10 s firingsc* efficiency from chamber pressure and measured flows
- Throttle steps100% to 60% and back, open-loop, then closed-loop on chamber pressure
- Showcase firingFilmed for sponsors and the milestone report
Same chamber pressure, half the thrust
The stand, sequencer, control loops, pintle fuel side, liner construction and procedures carry over unchanged. The lander engine swaps gaseous oxygen for liquid N2O and doubles the flow.
| Proof of concept | Lander engine | |
|---|---|---|
| Propellants | GOX and ethanol | Liquid N2O and ethanol |
| Thrust | 240 N → 400 N | 900 N |
| Chamber pressure | 9.5 → 15 bar | 15 bar |
| Mixture ratio | 1.3 | 3.5 |
| Total flow | 128 → 204 g/s | 496 g/s |
| Throat, chamber | Ø16, Ø40 mm | Ø25, Ø56 mm |
| Burn | 10 s | 20 s |
| Throttle | To 60%, 40% stretch | To 40%, held within ±5% |
| Oxidizer feed | Regulated gas | Self-pressurized liquid, 50–63 bar |
Phase-one budget
About R$13,100 in total, R$11,600 with borrowed safety gear. Estimates for late 2026, not quotes.