Specific Impulse Calculator
Calculate rocket engine performance and efficiency using thrust, mass flow rate, or exhaust velocity
Calculate Specific Impulse
Select a real rocket engine to auto-fill parameters, or use custom values
Force produced by the rocket engine
Rate of propellant consumption
Velocity of exhaust gases relative to the rocket
Standard Earth gravity: 9.80665 m/s² (can be adjusted for other planets)
Specific Impulse Results
Formula used: Isp = F / (ṁ × g)
Effective Exhaust Velocity: 0 m/s
Performance: Higher Isp indicates more efficient propellant use
Performance Analysis
Example Calculation
SpaceX Merlin 1D Engine
Thrust: 845,000 N (at sea level)
Mass Flow Rate: 273.6 kg/s
Exhaust Velocity: ~3,050 m/s
Propellants: RP-1 (kerosene) and liquid oxygen
Calculation
Isp = F / (ṁ × g)
Isp = 845,000 N / (273.6 kg/s × 9.80665 m/s²)
Isp = 845,000 / 2,683.9
Isp = 314.9 seconds
Engine Types Comparison
Solid Rocket Motors
150-250s Isp
Simple, reliable, lower performance
Kerosene/Oxygen
280-340s Isp
Good thrust, moderate efficiency
Hydrogen/Oxygen
380-450s Isp
High efficiency, lower thrust
Ion Propulsion
3000-10000s Isp
Extremely efficient, very low thrust
Specific Impulse Facts
Measured in seconds - time to consume propellant equal to engine weight
Higher Isp means better fuel efficiency
Depends on exhaust velocity and gravitational acceleration
Critical for spacecraft mission planning
Understanding Specific Impulse
What is Specific Impulse?
Specific impulse (Isp) is a measure of rocket engine efficiency. It represents how many seconds an engine can produce thrust equal to its weight using one unit of propellant. Higher specific impulse means better fuel efficiency and longer operating time.
Why is it Important?
- •Determines mission feasibility and payload capacity
- •Enables comparison between different engine types
- •Critical for calculating delta-v requirements
- •Helps optimize propellant selection
Formula Explanations
Isp = F / (ṁ × g)
- Isp: Specific impulse (seconds)
- F: Thrust force (Newtons)
- ṁ: Mass flow rate (kg/s)
- g: Gravitational acceleration (m/s²)
Isp = ve / g
- ve: Exhaust velocity (m/s)
- g: Gravitational acceleration (m/s²)
Note: TSFC (Thrust-Specific Fuel Consumption) is the inverse measure: fuel consumed per unit thrust produced.