Do rockets use gravity to hurl themselves into space?

Answer 1

First, rockets dont fly. In otherwords, birds fly because their wings give them "lift". Planes fly because wings provide "lift". "Lift" is required to counteract gravity and lift the bird or plane upwards, or at least prevent it from falling. The wings operate according to fluid dynamics (yes, air is characterized as a fluid in this case). Rockets are propelled by rocket engines. The rocket engine provide the "lift" to counteract gravity according to forces different than wings. Therefore, I claim rockets dont "fly". If there was no gravity things would "float". Once a rocket is in space one could argue that it is "floating" in space. However, gravity exists everywhere and to keep a rocket from "falling" towards an object like earth, it needs to move away from earth. When something is in earth orbit it is really moving away from earth. However, the gravitational pull of earth causes the object to fall a little towards the earth. The combination of moving away and falling makes the orbit circular or eliptical and makes it seem that it can do this forever. In fact, planets have been orbiting the sun for a long time with no additional energy. The rocket could do the same if it wasn't for other issues that cause it to slow down. As it slows down it cannot move away from the earth fast enough to counteract it falling towards the earth. Eventually, the orbit ceases without additional energy and the rocket floats (or falls) to earth. Because the space shuttle has wings it can float in a controlled manner back to a landing field after it is in the atmosphere (air). BTW, the shuttle's wings are useless in space because there is no fluid (ie air). Air is required to "fly". It could be said that fish "fly" in water but now we are delving into symantics.

Answer 2

No, at least not when they are leaving a planetary surface. However when traveling through the solar system they can avail themselves or a procedure known as a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the path and speed of the spacecraft.

The technique was first used Mariner 10. The Voyagers' also used it flybys of Jupiter and Saturn to propel themselves out of the solar system..