Specific Impulse Calculator

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Isp in seconds is the same in both systems; only thrust and flow rate labels change.
Choose which quantity you want to find.
Loads a representative vacuum Isp. Select Custom to enter all values manually.
Average thrust produced by the engine during the burn.
N
Mass of propellant consumed per second.
kg/s
Total rocket mass including all propellant at ignition.
kg
Rocket mass after all propellant is exhausted (structure + payload).
kg
Specific impulse (Isp)Liquid chemical range
311.2s

Thrust produced per unit weight-flow of propellant consumed

Effective exhaust velocity (Ve)3,052
Thrust (F)934,000
Mass flow rate (m-dot)306
Thrust-specific fuel consumption (TSFC)0.000328
Mass ratio (m0 / mf)12.5
Delta-V7,709
Burn time (approx.)751.6
311.2 s
Cold gas<100Solid rocket100-280Liquid chem.280-380Hi-perf chem.380+

Specific impulse: 311.2 s

  • An Isp of 311.2 s corresponds to an effective exhaust velocity of 3052 m/s.
  • This engine produces 934000 N of thrust while consuming 306.000 kg/s of propellant.
  • With a mass ratio of 12.50, the Tsiolkovsky equation gives a delta-V of 7709 m/s - enough for a significant orbital manoeuvre.
  • The propellant supply lasts approximately 751.6 seconds at this flow rate.
  • This is typical of hydrocarbon/LOX engines such as the Merlin or F-1.

Next stepTo maximise delta-V for a given Isp, reduce dry mass (structure and payload fraction). For chemical stages, a mass ratio of 7-10 is typical; ion stages often exceed 10.

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