Specific Impulse Converter

Convert specific impulse values between seconds, meters per second, feet per second, and kilometers per second. Specific impulse is a key metric for evaluating rocket engine efficiency.

Specific Impulse Value

Quick Reference

Conversion Results

Enter a specific impulse value

Use the quick reference or input your own value

Specific Impulse Theory & Notes

Definition

Specific Impulse (Isp) is a measure of how efficiently a rocket engine uses propellant. It represents the impulse (change in momentum) produced per unit of propellant mass consumed.

Mathematical Relationships

Primary Formula: Isp = F / (ṁ × g₀)

Where:

F = Thrust force (N)

ṁ = Mass flow rate (kg/s)

g₀ = Standard gravity = 9.80665 m/s²

Effective Exhaust Velocity: vₑ = Isp × g₀

Unit Conversions

Seconds: Isp in seconds (most common unit)
m/s: Effective exhaust velocity = Isp × 9.80665
ft/s: Effective exhaust velocity in feet per second = Isp × 32.174
km/s: Effective exhaust velocity in kilometers per second = Isp × 0.00980665

Physical Interpretation

Higher Isp means more efficient propellant usage
Isp represents the "gas mileage" of a rocket engine
Directly related to exhaust velocity - faster exhaust = higher Isp
Affects mission delta-v capability through the rocket equation

Performance Categories

< 200s: Low performance (cold gas, some monopropellants)

200-300s: Moderate performance (hydrazine, basic bipropellants)

300-400s: Good performance (LOX/RP-1, LOX/LH2)

400-500s: High performance (optimized LOX/LH2)

500-1000s: Very high performance (electric propulsion)

> 1000s: Exceptional performance (advanced electric, nuclear)

Common Applications

Cold Gas: 150-200s - Simple, reliable, low thrust
Monopropellant: 200-250s - Hydrazine for satellites
Bipropellant: 300-450s - Most launch vehicles and spacecraft
Electric Propulsion: 1000-5000s - Deep space missions, station keeping
Nuclear Thermal: 800-1000s - Proposed for Mars missions

Design Considerations

Higher Isp requires more complex engine designs
Electric propulsion has high Isp but low thrust
Chemical rockets balance Isp with thrust requirements
Mission requirements determine optimal Isp range
Cost and complexity increase with higher performance

Historical Context

The concept of specific impulse was developed in the early days of rocketry to compare different propellant combinations. It remains one of the most important metrics for evaluating propulsion system performance and mission feasibility.

Open Source & Transparent

This tool is open source and the underlying logic is fully transparent. You can view the source code, understand the calculations, and even contribute improvements to make it better for everyone.

View Source Code