Calculated Results
Results appear here after you press calculate.
Calculator Inputs
Use thrust mode for engine sizing from burn data. Use delta-v mode for mission mass estimation from the rocket equation.
Example Data Table
Sample inputs below illustrate both major sizing approaches used by propulsion teams.
| Case | Mode | Thrust (N) | Burn Time (s) | Specific Impulse (s) | Delta-v (m/s) | Dry + Payload Mass (kg) | Reserve (%) |
|---|---|---|---|---|---|---|---|
| Sounding Rocket | Thrust | 120,000 | 95 | 285 | — | — | 5 |
| Orbital Transfer | Delta-v | — | — | 320 | 3,200 | 2,150 | 8 |
| Upper Stage Check | Delta-v | — | — | 340 | 1,800 | 950 | 4 |
Formula Used
Two standard propulsion relationships are built into this calculator. In thrust mode, the mass flow rate is based on thrust divided by effective exhaust velocity:
ṁ = F / (Isp × g₀)
Base propellant mass is then:
mp = ṁ × tb
In delta-v mode, the Tsiolkovsky rocket equation estimates initial mass from mission delta-v:
Δv = Isp × g₀ × ln(m₀ / mf)
Rearranging gives:
m₀ = mf × e^(Δv / (Isp × g₀))
Then base propellant mass becomes:
mp = m₀ − mf
Reserve mass is added using:
mp,total = mp × (1 + reserve/100)
If an oxidizer-to-fuel ratio is provided, the calculator splits total propellant into oxidizer and fuel portions using:
Fuel = mp,total / (1 + O/F) and Oxidizer = mp,total − Fuel
How to Use This Calculator
- Select the calculation mode that matches your design problem.
- Choose your preferred output mass unit.
- Enter specific impulse and reserve margin.
- For thrust mode, fill thrust and burn time.
- For delta-v mode, enter delta-v, dry mass, and payload.
- Add an oxidizer-to-fuel ratio if you need mass split estimates.
- Enter stage count for equal per-stage planning values.
- Press the calculate button to show results above the form.
- Use the CSV or PDF buttons to export the result summary.
Frequently Asked Questions
1. What does propellant mass mean?
Propellant mass is the consumable working mass required to produce thrust or deliver a target delta-v. It excludes dry structure unless you include margin policies separately.
2. When should I use thrust mode?
Use thrust mode when engine thrust, burn duration, and specific impulse are already known. It is common during preliminary engine sizing and burn planning.
3. When should I use delta-v mode?
Use delta-v mode when mission velocity change is the main requirement. It helps estimate how much propellant the stage needs from dry mass and payload.
4. Why is reserve margin important?
Reserve margin covers uncertainty in performance, losses, boil-off, guidance corrections, and operational contingencies. Engineering teams often add it before freezing a mass budget.
5. Does the oxidizer-to-fuel ratio change total propellant mass?
No. It only splits total propellant into oxidizer and fuel components. Total propellant is determined by thrust or delta-v inputs and reserve settings.
6. Can this calculator model real staging exactly?
No. The stage field provides equal planning splits only. Real staging requires separate structure fractions, ignition losses, ullage needs, and stage-specific performance values.
7. What units does the calculator use internally?
It uses SI relationships internally for thrust, gravity, and delta-v. The mass unit selector changes displayed values between kilograms and pounds.
8. Is this suitable for final flight certification?
No. This tool is best for conceptual design, trade studies, and budget checks. Flight certification requires detailed subsystem data, validation, and formal review.