Gravity Turn - Use in Spaceflight

Use in Spaceflight

Many spaceflight missions have utilized the gravity turn, either directly or in a modified form, to carry out their missions. What follows is a short list of various mission that have used this procedure.

• Surveyor program — A precursor to the Apollo Program, the Surveyor Program's primary mission objective was to develop the ability to perform soft landings on the surface of the moon, through the use of an automated descent and landing program built into the lander. Although the landing procedure can be classified as a gravity turn descent, it differs from the technique most commonly employed in that it was shot from the Earth directly to the lunar surface, rather than first orbiting the moon as the Apollo landers did. Because of this the descent path was nearly vertical, although some "turning" was done by gravity during the landing.

• Apollo program — Launches of the Saturn V rocket during the Apollo program were carried out using a gravity turn in order to minimize lateral stress on the rocket. At the other end of their journey, the lunar landers utilized a gravity turn landing and ascent from the moon.

• Mariner 10 — The Mariner 10 mission used a gravity assist from the planet Venus to travel to Mercury. In 1970, three years before its launch, Giuseppe Colombo noticed that because the spacecraft's orbit around the Sun after the encounter with Mercury was very close to twice the orbital period of Mercury. By properly orienting the first flyby of Mercury the spacecraft underwent a gravity turn which allowed it to make a second flyby of the planet.

• Ulysses — The Ulysses probe utilized a gravity turn around Jupiter to change the inclination of its orbit around the sun. This was done because the delta-v required to launch into a polar orbit around the sun was greater than the capability of any existing rocket. The spacecraft left Earth, arriving at Jupiter slightly "below" it; this caused Jupiter's gravity to incline the orbit so the probe would pass over the Sun's "north" pole.