Calculator Inputs
Enter average mission values for a steady burn segment. This tool estimates ideal burn time and related performance using simplified engineering relationships.
Example Data Table
| Scenario | Propellant Mass (kg) | Dry Mass (kg) | Payload (kg) | Flow per Engine (kg/s) | Engines | Throttle (%) | Usable Propellant (%) | Isp (s) | Efficiency (%) |
|---|---|---|---|---|---|---|---|---|---|
| Reference stage burn | 1200 | 850 | 150 | 8.5 | 2 | 92 | 97 | 285 | 96 |
| Higher throttle check | 1200 | 850 | 150 | 8.5 | 2 | 100 | 97 | 285 | 96 |
| Single engine test | 450 | 500 | 60 | 4.2 | 1 | 88 | 95 | 250 | 94 |
Formula Used
1) Effective mass flow
ṁeff = ṁ × engines × throttle fraction
2) Usable propellant
musable = propellant mass × usable fraction
3) Burn time
tburn = musable / ṁeff
4) Effective exhaust velocity
ve = Isp × g × efficiency fraction
5) Average thrust
F = ṁeff × ve
6) Total impulse
Itotal = F × tburn
7) Ideal delta-v
Δv = ve × ln(m0 / mf)
This calculator assumes a steady average burn and uses idealized relationships. Real missions can differ because of mixture shifts, gravity losses, pressure changes, drag, and throttling schedules.
How to Use This Calculator
- Enter propellant, dry, and payload masses.
- Provide mass flow per engine and engine count.
- Set throttle percentage and usable propellant percentage.
- Enter specific impulse, efficiency, and gravity reference.
- Click Calculate Burn Time to generate results above the form.
- Review burn time, thrust, total impulse, thrust-to-weight, and ideal delta-v.
- Use the graph to inspect mass depletion and cumulative impulse over time.
- Export results to CSV or PDF for reporting and comparison.
Frequently Asked Questions
1) What does burn time mean?
Burn time is the estimated duration the engine can operate while consuming the usable propellant at the chosen average flow rate and throttle setting.
2) Why does throttle affect burn time?
Throttle changes the effective mass flow rate. Higher throttle usually consumes propellant faster, which shortens burn time if all other inputs stay unchanged.
3) Why include usable propellant percentage?
Not every kilogram of onboard propellant is always available for ideal consumption. Residuals, ullage needs, and operational limits can reduce usable propellant.
4) What is specific impulse?
Specific impulse measures propulsion efficiency. Larger values generally indicate more exhaust velocity and better potential delta-v for a given mass ratio.
5) Is delta-v here exact mission performance?
No. The displayed delta-v is idealized. Real vehicles lose performance through drag, steering, gravity losses, mixture changes, and off-design operation.
6) Why are ignition and burnout thrust-to-weight both shown?
Vehicle mass decreases during burn. Showing both values helps reveal how acceleration conditions improve as propellant is consumed.
7) Can I use this for multi-engine stages?
Yes. Enter the mass flow for one engine and provide the engine count. The tool scales effective flow and thrust accordingly.
8) Why export CSV or PDF?
Exports make it easier to document assumptions, compare cases, and share a clean summary with teammates, clients, or project files.