
DeltaV Calculator


Full Mass 

mass of the rocket plus fuel 
Dry Mass 

mass of the rocket after the burn 
Vex or Isp 

exhaust velocity
specific impulse

DeltaV 

change in velocity
= ln(full mass/dry mass) 


Mass units
are arbitrary; use whatever you like, as long as you're
consistent. Similarly,
Velocity units
are arbitrary; the deltaV
computed will be in the same units. Specific impulse is in seconds. Change in velocity, or deltaV, is the most important measure of
"distance" in space flight. To get from the ground to low Earth orbit
(LEO) requires a deltaV of about 8600 m/sec^2. To get from LEO to the
Moon requires a different deltaV. It's the clearest measure of how hard
a rocket has to work to change position.
Specific Impulse
is exhaust velocity divided by g,
the acceleration due to gravity on Earth's surface (9.80665 m/s^2). It's
a common measure of the "mass efficiency" of a rocket engine. You can use
the radio buttons above to convert between specific impulse and exhaust
velocity. The above calculator is very simplistic; it assumes no drag, and it
allows only a single burn. But it can be applied to a great many models.
For example, you could calculate the deltaV attainable by a baseball
pitcher, throwing baseballs to change his orbit. Or, if you know the
deltaV between an asteroid orbit and Earth orbit, you can calculate how
much mass you'd have to eject from the asteroid to park it (which of
course depends on how fast your mass launcher is). 