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Exoplanet Transit Fuel Requirements Estimator

Estimate propellant mass for a exoplanet-transit mission maneuver from spacecraft dry mass, required delta-v, propulsion specific impulse, and a propellant reserve.

The calculator applies the ideal rocket equation to a single equivalent maneuver. It is intended for early mass-budget trades, where the goal is to understand how propulsion efficiency and delta-v drive propellant demand before detailed trajectory and tank-sizing analyses are available.

Inputs

kg
m/s
s
%
Result
—
Propellant with reserve
Ideal propellant—
Wet mass with reserve—
Ideal mass ratio—

1. Enter dry mass
Use spacecraft mass remaining after the modeled burn, excluding the propellant consumed by that burn.

2. Enter mission delta-v
Use the total equivalent delta-v assigned to this propulsion calculation.

3. Enter specific impulse
Use the propulsion-system Isp appropriate to the planned maneuver.

4. Add a propellant reserve
The reserve is applied on top of the ideal propellant result.

5. Review mass impact
Use propellant and wet mass as preliminary mass-budget values, then replace assumptions with trajectory-specific data when available.

Mass ratio = exp(Δv / (Isp × g₀))
Ideal propellant = dry mass × (mass ratio − 1)
Propellant with reserve = ideal propellant × (1 + reserve%)

g₀ = 9.80665 m/s². This is the ideal Tsiolkovsky rocket equation represented as one equivalent burn.

What the result means

The result is a preliminary propellant allocation for the entered equivalent delta-v and propulsion efficiency.

Real mission budgets must include trajectory losses, maneuver dispersions, residuals, unusable propellant, and hardware mass as applicable.

Given: dry mass 1,200 kg, delta-v 650 m/s, Isp 230 s, and 12% reserve.

Calculation: Mass ratio = exp[650/(230 × 9.80665)] ≈ 1.3340. Ideal propellant = 1,200 × 0.3340 ≈ 400.8 kg. With 12% reserve: 400.8 × 1.12 ≈ 448.9 kg.

Result: Preliminary propellant allocation is about 448.9 kg, giving a wet mass near 1,648.9 kg.

Why is dry mass used as the final mass?

The ideal rocket equation compares mass before and after propellant is expelled. In this single-burn model, dry mass represents the mass remaining after the modeled propellant is consumed.

Does the reserve change the required delta-v?

No. The reserve is added after the ideal propellant calculation as extra carried propellant.

Can I combine several burns into one delta-v?

For a rough first pass, delta-v values can be combined into an equivalent total. Detailed missions should model staging, propellant use, and maneuver timing separately.

Does this include tank and propellant-system mass growth?

Only if those masses are already included in the dry-mass input. The calculator does not independently size tanks or feed systems.

Why does higher Isp reduce propellant?

Higher specific impulse increases effective exhaust velocity, so less propellant is needed for the same ideal delta-v and final mass.