Ariane 5 Kourou
Specific impulse is the parameter used to measure the efficiency of a rocket jet engine, and is basically the ratio of the useful jet impulse Ft (Ns) produced divided by the fuel flowrate (mass per second in Kg/sec) required to produce that impulse . Specific impulse Isp is the index of performance for rocket engines and is defined by the following ratio : sec

Where the numerator is the total impulse obtained over the operating time of the rocket engine. Usually referred to as the ‘Burn time’. Defined by the time period from t_{0} to t_{1}.seconds. Accompanied by a denominator which represents the total fuel mass flow necessary to produce the impulse during the same time period. ‘g’ is the acceleration due to gravity g_{earth} at sea level m/s^{2} The above expression can be simplified to the ratio given below if the flow rate and thrust are constant over the burn time. For liquid fueled rocket engines this is usually the case, so they can be represented by the ratio of the thrust force produced at the exit of the nozzle F _{ } divided by the product of g_{earth} at sea level multiplied by the mass flow rate of fuel used to produce the thrust. Note: F is measured at t_{earth} Specfic impulse I_{sp} = sec

Where F is the Jet Thrust force at the outlet of the nozzle F = q * v_{2 }N _{Newtons } ‘q’ is the volumetric flowrate * density r to give mass flowrate of fluid leaving the nozzle Kgs/sec v_{2 }is the exhaust jet velocity at the outlet of the nozzle m/sec Mdt is the mass flowrate of fuel

Dimensional analysis of I_{sp} Isp = Sec

Isp = Sec

esa comparison of specific impulse for liquid propergols and electric propulsion Once you are out in space and have overcome aerodynamic drag of the atmosphere then the total impulse produced over a long period by a certain mass of fuel become significant.
http://sci.esa.int/sciencee/www/object/index.cfm?fobjectid=34201 Definition of Tsiolkovskis Formula Tsiolkovski modified end function http://en.wikipedia.org/wiki/Specific_impulse
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This site was created on the 15th April 2003 ©John Gwynn and sons2003 You're welcome to reproduce any material on this site for educational or other non commercial purposes as long as you give us proper credit (by referring to "The WaterRocket Explorer" http://waterocket.explorer.free.fr).


Ariane 5 Envisat 2 
" Great things are not done by impulse, but a
series of small things brought together". Ironic quotation which says that success is the result of assembling many simple existng systems or ideas in a new original way. 