Rocket Engine Specific Impulse Calculator

Specific Impulse Equation:

\[ I_{sp} = \frac{v_e}{g} \]

Specific Impulse (I_sp):

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1. What is Specific Impulse?

Specific impulse (I_sp) is a measure of how efficiently a rocket engine uses propellant. It represents the impulse (change in momentum) per unit of propellant and is equivalent to the exhaust velocity divided by gravitational acceleration.

2. How Does the Calculator Work?

The calculator uses the specific impulse equation:

\[ I_{sp} = \frac{v_e}{g} \]

Where:

\( I_{sp} \) — Specific impulse (seconds)
\( v_e \) — Exhaust velocity (m/s)
\( g \) — Standard gravity (9.81 m/s²)

Explanation: The equation shows that specific impulse is directly proportional to exhaust velocity and inversely proportional to gravitational acceleration.

3. Importance of Specific Impulse

Details: Specific impulse is crucial for comparing rocket engine performance. Higher I_sp means more efficient propellant usage, allowing for greater payload capacity or longer missions.

4. Using the Calculator

Tips: Enter exhaust velocity in m/s and gravitational acceleration (default is Earth's gravity at 9.81 m/s²). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical I_sp values for different engines?
A: Chemical rockets: 250-450s, Ion thrusters: 2000-5000s, Nuclear thermal: 800-1000s.

Q2: Why measure I_sp in seconds?
A: The units work out to seconds dimensionally, and it represents how long 1kg of propellant can produce 1kg of thrust.

Q3: How does I_sp relate to thrust?
A: Thrust = I_sp × g × mass flow rate. Higher I_sp means more thrust per unit of propellant.

Q4: What affects exhaust velocity?
A: Combustion temperature, molecular weight of exhaust products, and expansion ratio.

Q5: Can I_sp be improved?
A: Yes, through higher combustion temperatures, lighter exhaust products, or more efficient nozzle expansion.