No waiting, but the real distance: why jump fuel works as it does
Published
Only the carrier and the Hawkeye scout have jump drives. Here is why a jump costs what it costs.
A jump costs the fuel of the real trip
Why: “no waiting, but the cost of the real distance”. A jump is instant once the drive has spooled, but it burns the fuel the trip would have taken if it were flown.
Decided 2026-10-25 · scripts/warp_fuel.gd
Fuel from the rocket equation
Why: fuel from physics, “a base rule to reuse for every ship”: nothing hand-picked. The game uses Tsiolkovsky’s rocket equation, published in 1903[2], solved for the fuel burned: fuel = mass × (1 − e^(−Δv ÷ v_e)). Because fuel is mass you also have to push, far trips cost far more than near ones: Pluto costs about 36 carrier tanks, the Moon about a tenth of one.
Decided 2026-10-25 · scripts/warp_fuel.gd cost_dv()
1 g the whole way
Why: 1 g is livable for a crew. The ship speeds up to the halfway point, flips and brakes, so trip time = 2 × √(distance ÷ 9.81 m/s²): the Moon in about 3.5 hours. The project’s own note is honest about it: nothing real holds 1 g for hours.
Decided 2026-10-25 · scripts/warp_fuel.gd ACCEL = 9.81
A 10,000 km/s exhaust
Why: the one number physics can’t give, so it is a stated assumption with a source: a fusion drive of the kind studied in Project Daedalus, whose two stages were designed for exhaust velocities of 10,600 and 9,210 km/s[1].
Decided 2026-10-25 · scripts/warp_fuel.gd EXHAUST = 1.0e7 (m/s)
Not a cost per kilometre
Why: a cost per kilometre, like a ship at sea, grows straight with distance. Under the rocket equation the cost grows faster than the distance, because you push your own fuel. That is what makes deep trips expeditions.
Decided 2026-10-25 · scripts/warp_fuel.gd
Hot drops and burns cost nothing
Why: “nobody should waste time saving slivers of fuel”.
Decided 2026-10-25 · scripts/warp_fuel.gd (header)
The carrier: 100,000 t and a 10,000 m³ tank
Why: every ship is anchored on a real counterpart of its size and role. The carrier’s is the Nimitz class, about 100,000 long tons at full load[3]. The 10,000 m³ tank is anchored on a Nimitz’s jet-fuel load: about three million gallons of JP-5[5], roughly 11,400 m³ (derived: 3 million US gallons × 3.785 litres).
Decided 2026-10-25 · scripts/ship_catalog.gd MASS["Imperial"] = 100,000 t; modules.gd TYPES["fuel_tanks"] = 10,000 m³
The Hawkeye: 18.4 t and a 7 m³ tank
Why: the same rule. The Hawkeye is anchored on the E-2 Hawkeye, 18,234 kg empty[4]; the game rounds it to 18.4 t. Its 7 m³ tank is anchored on the E-2’s internal fuel, 5,624 kg usable[6]: about 7 m³ of jet fuel. With the same drive it gets about 3,200 km/s from a full tank, around 28 trips to the Moon.
Decided 2026-10-25 · scripts/ship_catalog.gd MASS["Hawkeye"] = 18.4 t; modules.gd TYPES["fuel_tank"] = 7 m³
Fuel weighs 1 t a cubic metre; cargo 0.7
Why: a ship’s mass is its hull with its fit, plus what is in its hold, plus its fuel. A heavier ship burns more for the same trip: a full carrier hold costs about 25 % more fuel a jump. 1 t a cubic metre for fuel and 0.7 for cargo are round in-game defaults.
Decided 2026-10-25 · scripts/warp_fuel.gd FUEL_DENSITY = 1.0, HOLD_DENSITY = 0.7
Fuel in containers takes a third more room
Why: fuel in the hold travels in tank containers, which need room for their frame. 100 m³ of fuel fills 100 m³ of tank, or about 133 m³ of hold. Tanks are the efficient way; containers are flexible, because the room is cargo again once the fuel is burned. The one-third figure is an in-game estimate.
Decided 2026-10-25 · scripts/items.gd TYPES["fuel"]
Range is all the fuel aboard
Why: a ship tops its tanks up from its own hold on the way, so a long route is one order, with its cost added up over the links. The game shows before the jump whether the fuel left would bring the ship back.
Built 2026-10-25 · scripts/warp_fuel.gd can_return_dv(), top_up()
Spool: 12 s for the carrier, 4 s for the Hawkeye
Why: bigger ships take longer; there is no cool-down. A route of several links spools that many times as long, a 3-link carrier route 36 seconds: a window in which it can be caught. Both times are placeholders.
Built 2026-10-23 · scripts/ship_catalog.gd JUMP_DRIVES
Related
- 36 tanks to Pluto: jump fuel from the rocket equation
- Why fuel is mass: the rocket equation, explained
- 350 m, just above the longest ship ever: why the carrier is built as it is
- Fun first, real numbers as flavour: how the game is designed
Sources
- Project Daedalus, Wikipedia.
producing exhaust velocities of 10,600 km/s and 9,210 km/s respectively.
- Tsiolkovsky rocket equation, Wikipedia.
The equation is named after—and usually credited to—Konstantin Tsiolkovsky, who derived and published the formula in 1903.
- Nimitz-class aircraft carrier, Wikipedia.
100,000 to 104,600 long tons (101,600–106,300 t) full load
- Northrop Grumman E-2 Hawkeye: specifications, Wikipedia.
Empty weight: 40,200 lb (18,234 kg)
- Fuel in potable water system delays deployment of carrier USS Nimitz, The Maritime Executive.
Nimitz-class carriers can carry about three million gallons of JP-5 on board
- E-2C Hawkeye, Federation of American Scientists.
Maximum fuel (internal, usable) 5,624 kg