macro that uses local variables

[Heime]

I am using the rocket equation in this macro.  I want to change it such that
the arguments are set as local variables.  How does one code that ?

(defmacro booster-velocity-change
    (specific-impulse standard-gravity initial-mass final-mass)

  "Compute change of velocity using rocket equation."

  `(* (* ,specific-impulse ,standard-gravity)
        (log (mass-ratio ,initial-mass ,final-mass))) )