Where V _ \ mathrm { e } is the effective exhaust velocity, M _ { \ mathrm { initial } } the initial mass, and M _ { \ mathrm { final } } the mass of the rocket at the point of burnout of each stage.
22.
The specific impulse in terms of propellant mass spent ( multiplying the weight-based " I " sp in seconds by " g " 0 ) is in units of distance per time, which is an artificial velocity called the " effective exhaust velocity ".
23.
To attain and maintain such high speeds, Reaction Engines Limited would need to develop its newly designed concept engine called the Scimitar, which exploits the Mach 5 throughout flight with an effective exhaust velocity of 40, 900 m / s or specific impulse of 4170 s, SFC.
24.
This is termed " exhaust velocity ", and after allowance is made for factors that can reduce it, the "'effective exhaust velocity "'is one of the most important parameters of a rocket engine ( although weight, cost, ease of manufacture etc . are usually also very important ).
25.
Where \ displaystyle m _ f / m _ 0 is the ratio of final mass to initial mass ( i . e ., one minus the mass fraction ), \ displaystyle \ Delta v is the change in the vehicle's velocity as a result of the fuel burn and \ displaystyle v _ e is the effective exhaust velocity ( see below ).
26.
Note that "'effective "'exhaust velocity and "'actual "'exhaust velocity can be significantly different, for example when a rocket is run within the atmosphere, atmospheric pressure on the outside of the engine causes a retarding force that reduces the specific impulse, and the effective exhaust velocity goes down, whereas the actual exhaust velocity is largely unaffected.
27.
(The equation can also be written using the specific impulse instead of the effective exhaust velocity by applying the formula v _ \ text { e } = I _ \ text { sp } \ cdot g _ 0 where I _ \ text { sp } is the specific impulse expressed as a time period and g _ 0 is standard gravity H " 9.8 m / s 2 .)
