Because of the exponential nature of the rocket equation the orbital rocket needs to be considerably bigger.

This is the more frequently proposed method, but is fundamentally limited in final spacecraft velocities by the rocket equation.

The relationship is described by the rocket equation: .

The rocket equation shows that the required amount of propellant dramatically increases, with increasing delta-v.

Which is just the rocket equation applied to the sum of the two maneuvers.

The mass fraction plays an important role in the rocket equation:

If done by direct propulsion, the rocket equation dictates that a large fraction of the spacecraft mass must be fuel.

As a child he had discussed the possibilities of humans in space with his parents, and in college he enjoyed working on rocket equations.

This comes to an exhaust velocity of about of the mission delta-v (see the energy computed from the rocket equation).

These values are used in equations similar to the rocket equation and are analogous to specific impulse or exhaust velocity.