 <unk> from Earth to other planets in the Solar System have a high energy cost . It requires almost the same amount of energy for a spacecraft to reach Jupiter from Earth 's orbit as it does to lift it into orbit in the first place . In <unk> , this energy expenditure is defined by the net change in the spacecraft 's velocity , or delta @-@ v. The energy needed to reach Jupiter from an Earth orbit requires a delta @-@ v of about 9 km / s , compared to the 9 @.@ 0 – 9 @.@ 5 km / s to reach a low Earth orbit from the ground . Gravity assists through planetary flybys ( such as by Earth or Venus ) can be used to reduce the energetic requirement ( i.e. the fuel ) at launch , at the cost of a significantly longer flight duration to reach a target such as Jupiter when compared to the direct trajectory . Ion <unk> capable of a delta @-@ v of more than 10 kilometers / s were used on the Dawn spacecraft . This is more than enough delta @-@ v to do a Jupiter fly @-@ by mission from a solar orbit of the same radius as that of Earth without gravity assist . 
