How this calculator works
Delta-v is the ideal change in velocity available from a burn, not the vehicle's final speed. Specific impulse is converted to effective exhaust velocity using standard gravity, 9.80665 m/s2. Initial mass includes propellant; final mass includes everything left after the burn. The single-stage model assumes constant effective exhaust velocity and excludes gravity, drag and steering losses.
Formula
delta-v = ve ln(m0/mf) = Isp g0 ln(m0/mf). m0 = mf exp(delta-v/ve); mf = m0 exp(-delta-v/ve); Isp = ve/g0.
Worked example
With effective exhaust speed 1000 m/s and a mass ratio of two, delta-v is 693.147 m/s. The same delta-v with 3 kg remaining requires an initial mass of 6 kg.
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Frequently asked questions
Is delta-v the same as speed?
It is a velocity-change budget. Gravity and the direction and timing of burns determine the resulting trajectory.
Which gravity converts specific impulse?
The conventional standard acceleration 9.80665 m/s2, even for a burn far from Earth.
Can wet and final masses be equal?
Yes, then no propellant is spent and ideal delta-v is zero. That case cannot determine a unique exhaust speed.