Expanse Delta-v Calculator
How long would it take to reach nearby stars with a drive similar to the Epstein Drive from The Expanse?
Drive & Mission
Fraction of fuel rest-mass converted to exhaust KE. ve = c·√(2η).
Spacecraft mass without propellant.
Sets thrust via F = m₀·a₀. Acceleration rises during the burn as fuel is spent.
Trip to Tau Ceti
Ship Time
48 years, 8 months
Earth Time
50 years, 1 months
Drive & Fuel
- Mass ratio (m₀/m_dry):44.47
- Fuel mass:21.73 kt
- Initial wet mass:22.23 kt
- Thrust:65,409,920 N
- Mass flow:2 kg/s
- Jet power:1.24 PW
Journey Phases
- Flight plan:Accelerate → Cruise → Decelerate
- Burn phase (each):4 months, 4 days
- Coast phase:49 years, 5 months
- Phase ratio:102% coasting
Journey Details
- Distance:11.91 light-years
- Mission Δv:143,900 km/s (0.48c)
- Peak velocity:71,950 km/s (24.00%c)
- Lorentz γ:1.030×
- Time dilation:1.030×
How long would it take to reach nearby stars with an Epstein-style fusion drive? Pick a drive efficiency, a dry mass, and a target cruise velocity, and the calculator works the trip out from the Tsiolkovsky rocket equation. Efficiency η sets the exhaust velocity via ve = c·√(2η), which sets the fuel mass ratio exp(2·Δv/ve), which sets everything else — fuel mass, burn time, burn distance, and the jet power the drive has to sustain. Crank η down to 0.65% and you'll see why an Epstein Drive needs to be fictional.
Physics review courtesy of Phil Fairman (retired physicist), who caught the earlier version's linear fuel-mass approximation and the unused efficiency parameter. if you spot anything else. Canon specs from Project Rho and the Expanse wiki.