Motion of Rocket in Outer Space

Theorem
Let $B$ be a rocket travelling in outer space.

Let the velocity of $B$ at time $t$ be $\mathbf v$.

Let the mass of $B$ at time $t$ be $m$.

Let the exhaust velocity of $B$ be constant at $\mathbf b$.

Then the equation of motion of $B$ is given by:
 * $m \dfrac {\d \mathbf v} {\d t} = - \mathbf b \dfrac {\mathrm d m} {\d t}$