It takes longer, but we'll make the top still with breath to enjoy the view and take pictures. A spacecraft on a journey with its limited allotment of energy also has to overcome gravity. With a spacecraft, we must first escape Earth's gravity to reach low-Earth orbit. Once we leave Earth-orbit, other gravitational influences become important in ways we don't need to consider when we are Earthbound. Spacecraft must steer through the curvature of space-time taking into account the accelerating effects of gravitation created by the Sun, planets, and other planetary objects.
Gravitational forces create warps in space-time.
We often speak of such warps as gravity wells, in the sense that it takes a great deal of energy to climb out of a well once you have fallen in. Upon close approach we can use a gravity assist to slingshot around the planet, accelerating to reach our true destination even faster. While we characterize a gravity assist by the planet the spacecraft goes near, it's not just the planet that does the trick. Gravity assist refers to the technique of borrowing energy by means of a close planetary flyby. Using vector analysis, we can plan a gravity assist.