About the Delta-V Budget Calculator
Every space mission is planned in delta-v: the sum of all velocity changes needed to get from one place to another. This tool lets you assemble a mission from standard legs - low Earth orbit to trans-lunar injection, lunar orbit to the surface, Earth to Mars transfer - and then applies the Tsiolkovsky rocket equation to show what your vehicle needs to fly it: mass ratio, propellant load, and whether the mission closes at all.
How to use it
- Tick the legs that make up your mission - the running total updates instantly.
- Add a margin (10% is a common planning buffer).
- Set your vehicle's Isp and dry mass.
- Read the required propellant and mass ratio, and check the chart of each leg's contribution.
- Share the exact scenario with the permalink button.
How it works
The mission total is the sum of selected leg delta-vs times your margin. The rocket equation then gives the required mass ratio: m0/mf = e^(dv / (Isp x g0)). With your dry mass fixed, propellant is (mass ratio - 1) x dry mass. Because the relationship is exponential, watch how adding one leg can double the propellant requirement - this is exactly why orbital refueling changes mission design so profoundly.
Worked example
LEO to TLI (3,120 m/s) plus TLI to low lunar orbit (900 m/s) plus landing (1,870 m/s) with 10% margin totals about 6,479 m/s. A methalox vehicle at Isp 380 s needs a mass ratio of about 5.7 - roughly 4.7 tonnes of propellant per tonne of dry vehicle.
Frequently asked questions
What is delta-v in one sentence?
Delta-v is the total change in velocity a spacecraft can produce - the 'fuel currency' of spaceflight that every maneuver spends.
What is the Tsiolkovsky rocket equation?
dv = Isp x g0 x ln(wet mass / dry mass). It says achievable delta-v grows with exhaust efficiency (Isp) and the ratio of fueled to empty mass.
Why do small dv increases need so much more propellant?
Because mass ratio grows exponentially: each extra m/s of delta-v multiplies the required propellant fraction, which is why staging and refueling matter.
Are the mission leg values exact?
They are widely used textbook approximations (e.g. LEO to TLI about 3,120 m/s). Real missions vary with trajectory, timing, and margins.
Is my data uploaded?
No - everything runs in your browser. Nothing is sent to a server.