Kerbal Space Program Delta‑V Calculator

Formula Used

The calculator applies the Tsiolkovsky rocket equation independently to every active stage, then adds stage results in flight order.

Delta‑v is ideal velocity change. Isp is specific impulse. Standard gravity is 9.80665 m/s². Initial mass includes propellant and carried mass. Final mass includes dry hardware, payload, upper stages, and residual fuel.

How to Use This Calculator

1. Select a reference body.
2. Enter final payload and equipment masses.
3. Add stages from bottom to top.
4. Select an engine preset or enter custom values.
5. Enter stage dry mass, fuel, pressure, and separation mass.
6. Build the mission sequence.
7. Add realistic reserves.
8. Calculate and review warnings, TWR, burn time, and mission coverage.
9. Export JSON, CSV, PDF, or a share link.

Detailed Design Guide

Overview

This application combines a staged rocket equation calculator, mission budget planner, payload solver, fuel estimator, body reference table, engine library, validation system, and export tools. It is intended for pre-flight design checks. It does not replace in-game testing.

Stage ordering

Enter stages from the lowest active stage to the final upper stage. Automatic stacking carries every later stage during an earlier burn. After the burn, entered jettison mass is removed before the next stage begins.

Mass accounting

Dry mass should include tanks, structure, engines, decouplers, landing legs, batteries, reaction wheels, science parts, and other hardware assigned to that stage. Propellant mass should include only usable resources. Payload mass should describe hardware that remains with the final vehicle.

Engine mass option

The engine-mass checkbox is optional. Enable it only when stage dry mass excludes engines. Leaving it disabled is safest when copying a complete stage dry mass from another design tool.

Residual fuel

Residual fuel represents propellant intentionally reserved or trapped after a stage burn. It remains in final burn mass and reduces available delta-v. When the residual-fuel option is disabled, the calculator assumes all entered propellant can be consumed.

Atmospheric interpolation

The tool linearly interpolates thrust and specific impulse between sea-level and vacuum endpoints. This is useful for planning, but it does not reproduce every engine pressure curve exactly. Jet engines require a much more detailed model.

TWR

Thrust-to-weight ratio uses selected-body gravity. Launch and powered landing stages normally need TWR above one. Orbital transfer stages may use lower TWR, although burns become longer and maneuver accuracy can suffer.

Burn time

Fuel flow is estimated from thrust divided by specific impulse and standard gravity. Burn time is usable propellant divided by fuel flow. Long burns may need node centering, multiple periapsis passes, or a different engine cluster.

Engine-out mode

The engine-out field removes the selected number of engines from each multi-engine stage. It reports the starting TWR that remains. This does not model asymmetric thrust, gimbal authority, or structural control problems.

Mission legs

Each mission leg has a base delta-v, margin, optional aerobraking reduction, and optional gravity-assist reduction. Reductions should be used only when the trajectory genuinely supports them.

Reserve strategies

Per-leg margins are best when landing, docking, and transfer operations need different reserves. A global percentage is useful for simple planning. A fixed reserve is helpful when a known emergency or rendezvous allowance must remain.

Payload solver

The payload solver rearranges the rocket equation. It assumes one ideal stage. Structural mass, tank dry mass, engine mass, and staging hardware must be included for a practical design.

Fuel solver

Required fuel is derived from target delta-v, final mass, and specific impulse. Whole-tank rounding is available. After choosing tanks, add their dry mass and repeat the full calculation.

Asparagus staging

Represent each booster-drop event as a separate stage. Enter only the fuel consumed before that separation. Jettison mass should include empty tanks, engines, decouplers, and support hardware removed at that event.

Drop tanks

A drop tank can be modeled as a stage with no separate engine. Its fuel can be assigned to the engine stage and its empty tank mass entered as jettisoned mass at the drop event.

Solid boosters

Solid motors usually cannot throttle after ignition. Use a throttle value of one hundred percent and adjust thrust values to represent thrust limiting. Burn time remains an ideal average.

Nuclear stages

Nuclear engines provide high vacuum efficiency but low thrust. Check burn time carefully. A vehicle may have enough delta-v yet perform poorly for capture burns near periapsis.

Ion stages

Ion engines can provide enormous ideal delta-v. Their power requirements and very long burns are mission-critical. The calculator does not simulate solar output, battery depletion, eclipse time, or xenon feed systems.

Spaceplanes

Rocket-mode delta-v is straightforward. Air-breathing performance depends on altitude, speed, intake supply, drag, and engine curves. Jet presets are rough placeholders rather than full ascent simulation.

Landing design

A landing stage needs both delta-v and TWR. Include hover, correction, and reserve requirements. Terrain, piloting, horizontal velocity, and suicide-burn timing can materially change the result.

Launch design

A launch stage should be evaluated at representative pressure. A pressure of one atmosphere is conservative for ignition. A lower average pressure can approximate the full burn, but ascent drag and gravity losses remain outside the ideal equation.

Rendezvous

Budget separate delta-v for phasing, inclination correction, approach, braking, docking retries, and departure. Small spacecraft may need a larger percentage reserve because absolute corrections remain similar.

Aerobraking

Aerobraking can reduce capture or landing propellant. It introduces heating, structural, periapsis, and atmospheric uncertainty. Do not enter a large reduction without a tested heat shield and trajectory.

Gravity assists

Gravity assists can reduce propulsive requirements but add launch-window, encounter, and correction constraints. Treat the reduction as an advanced planning estimate.

Custom bodies

The custom body option accepts custom gravity and pressure. Modded systems can be represented by changing these values and using custom mission legs.

Exports

JSON stores the editable vessel configuration. CSV stores stage results. PDF creates a printable mission report. Browser storage saves one working design locally. Share links encode the configuration in the URL.

Validation

Warnings identify common data problems. They are not a complete flight-safety assessment. The calculator does not model aerodynamics, center of mass, center of lift, heating, part strength, communications, electricity, or life support.

Verification

Compare final values with the in-game engineer report. Confirm staging order, crossfeed, engine mode, locked tanks, and atmospheric condition. Differences usually come from mass accounting or resource flow.

Frequently Asked Questions