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What is a rocket made of?
A rocket is a stack, from bottom to top: one rocket engine on flat ground (with four landing legs), one to four tanks, zero to two cargo modules, a satellite deployer if you launch one, one cockpit and one fairing. It can fly only when the stack is complete in that order. The engine's 340 kg of propellant a second give about 1.1 MN of thrust, and the throttle is cut back above 4 g.
- Engine: 3.4 m high, 1 600 kg. The first piece, placed on the ground.
- Tank: 6 m, 1 000 kg dry, 26 m³ of propellant shared between oxidizer and fuel.
- Cargo module: 4 m, 1 500 kg. A hold of 36 slots that flies with you (72 with two); a full stack weighs 50 kg.
- Cockpit: 3 m, 2 400 kg. The crew capsule, four seats: right-click it to board; leashed animals board too.
- Fairing: 2.6 m, 400 kg. It shields the rocket from re-entry heat.
Which propellant should I use?
Every rocket burns liquid oxygen (LOX) with one of three fuels, one fuel per rocket. A dewar is one cubic metre of liquid; a tank holds 26 m³. The higher the Isp (in seconds), the more speed you get from the same mass.
| Fuel | Isp sea level / vacuum | Density | Dewars in a tank (LOX + fuel) | Character |
|---|---|---|---|---|
| Liquid methane | 327 / 350 s | 423 kg/m³ | about 15 + 11 | Balanced; the all-round choice. |
| RP-1 kerosene | 282 / 311 s | 810 kg/m³ | about 17 + 9 | The densest, the least efficient. |
| Liquid hydrogen | 366 / 452 s | 71 kg/m³ | about 7 + 19 | The most efficient, but very light: 2.3 times less per tank. |
| Propellant | Density (kg/m³) | Boils at | O/F ratio | Isp sea level / vacuum |
|---|---|---|---|---|
| Liquid oxygen (LOX) | 1141 | 90.2 K | — | — |
| Liquid methane (CH4) | 423 | 111.7 K | 3.6 | 327 / 350 s |
| RP-1 kerosene | 810 | 489 K | 2.56 | 282 / 311 s |
| Liquid hydrogen (LH2) | 71 | 20.3 K | 6 | 366 / 452 s |
| Tanks | CH4 | RP-1 | LH2 |
|---|---|---|---|
| 1 | 5746 m/s 26.7 t | 5624 m/s 31.6 t | 4692 m/s 14.4 t |
| 2 | 7232 m/s 49.3 t | 6983 m/s 59.2 t | 6293 m/s 24.8 t |
| 3 | 8000 m/s 72 t | 7680 m/s 86.8 t | 7163 m/s 35.2 t |
| 4 | 8481 m/s 94.7 t | 8115 m/s 114.4 t | 7718 m/s 45.6 t |
| Tank volume | 26 m³ |
|---|---|
| Tanks | 4 |
| Cargo modules | 2 |
| Slots per cargo module | 36 |
| Engine mass flow | 340 kg/s |
| Max acceleration | 4 g |
| Rocket radius | 1.5 m |
| Standard gravity | 9.81 m/s² |
What your stack can do (no cargo, full tanks), in kilometres a second of delta-v:
| Tanks | Methane | Kerosene | Hydrogen | Enough for |
|---|---|---|---|---|
| 1 | 5.5 | 5.4 | 4.5 | Low orbit (4.2) and a landing back |
| 2 | 7.0 | 6.8 | 6.1 | A landing on the Moon |
| 3 | 7.8 | 7.5 | 7.0 | More margin, or cargo |
| 4 | 8.3 | 8.0 | 7.5 | The Moon there and back |
How do I build, fuel and fly one?
- 1
Place the engine
Right-click flat ground holding the engine. Then right-click the rocket with each part in order: tanks, cargo modules, the deployer, cockpit, fairing. Hold the left click to take the top part back.
- 2
Open the rocket's screen
Right-click the rocket with anything else. Drag dewars of LOX and of one fuel in from your inventory: all the tanks fill at the right mixture. In survival an emptied dewar comes back empty.
- 3
Choose a destination and read the plan
The screen gives the route, the distance, the delta-v needed against the one you have, what the cargo costs, and simulates the whole flight: for instance “Lands on the point with 34 % propellant left”.
- 4
Board and light the engine
Press Board, then Space to light the engine. P hands the flight to the autopilot, which climbs, enters orbit, burns for the Moon and lands. Steering takes the controls back: Shift and Ctrl set the throttle, W A S D tilt the nose, N picks the destination.
- 5
Land upright
Deploy the legs with G. Under 3 m/s vertically and 2.5 m/s sideways, upright, is a good landing.
Where does the propellant come from?
- Empty dewars: steel flasks padded and sealed in epoxy, four at a time. Every propellant is one cubic metre in a dewar.
- Liquid oxygen (LOX): the gas plant fills an empty dewar with 64 units of oxygen, from its holder or straight from the air where there is air.
- Liquid methane and liquid hydrogen: the gas plant again, from natural gas (the refinery's fractions) or from hydrogen (water split into hydrogen and oxygen at the gas plant, or 32 voxels of water). On the Moon, Moon ice gives both LOX and hydrogen.
- RP-1: the refinery fills an empty dewar with 64 voxels of kerosene.
- Fill by conveyor: a fueling tower beside the pad takes 9 full dewars and pours one every 0.5 s into the nearest rocket (12 m around, 20 m up), returning 9 empties. A methalox tank wants about 15 LOX and 11 methane.
Questions
Why will my rocket not take off?
Check that the stack is complete in order (engine, tank, cockpit, fairing) and that tanks hold LOX and a fuel. The engine is lit with the Space key once aboard.
Which fuel is best?
Methane is balanced and is the sensible default. Hydrogen gives the most speed per kilogram but a tank holds 2.3 times less; kerosene is dense but least efficient.
How much does cargo cost me?
A full stack weighs 50 kg, a full hold of 36 slots 1.8 t. The rocket's screen computes the delta-v lost and the most the cargo can weigh for your trip.
Can I mix two fuels?
No. A rocket carries one fuel, chosen by the first one you load; empty the tanks with Drain to change it.
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