Leaving Earth

At our present level of technology, all interplanetary journeys must start from the Earth surface, i.e. deep into the gravitational well of Earth, and are also concluded on the surface of Earth. Exiting from this gravitational well is one of the most difficult and costly phases of all interplanetary missions. A similar situation occurs in the return journey, which must start from the surface of the destination planet. Also the opposite maneuver, a safe entry, descent and landing on the destination planet, is difficult even if, in the case of planets with an atmosphere, aerodynamic forces may be of help in reducing the cost of this phase of the journey. The final phase, re-entry into the Earth atmosphere, is also a difficult, and even dangerous, maneuver.