Question

How did scientists boost the spacecraft Juno on its way to Jupiter, helping it overcome the gravitational pull of the Sun?

Answer 1

the excerts force in backward direction
so rocket moves forward

Answer 2

By using the gravitational slingshot, the spacecraft Juno on its way to Jupiter was boosted by the scientist and also helping to get rid of the gravitational pull of the Sun.  

The Juno means the NASA space probe orbiting the Jupiter. The maximum speed of the Juno is 265000 km/hr. This was launched in 2011.