Motion of Rocket in Outer Space

Theorem
Let $B$ be a rocket of mass $m$ be 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 velocity of the rocket's exhaust be constant at $\mathbf b$.

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