To achieve an orbit, a spacecraft must travel faster than a sub-orbital spaceflight along an arcing trajectory. The energy required to reach Earth orbital velocity at an altitude of is about 36 MJ/kg, which is six times the energy needed merely to climb to the corresponding altitude. The escape velocity required to pull free of Earth's gravitational field altogether and move into interplanetary space is about .
To achieve an orbit, a spacecraft must travel faster than a sub-orbital spaceflight along an arcing trajectory. The energy required to reach Ear?th orbital velocity at an: altitude of is about 36 MJ/:kg, which is six times the energy needed merely to climb to the corresponding altitude. The escape velocity required to pull ,free of Earth's g?ravitational field altogether and move into interplanetary space is about .