Gravity Assist

gravity assist

by Mattia Costantino

Liceo Democrito 5C

gravity assist

In orbital mechanic the gravity assist is the use of the relative movement and gravity of an astronomical object in order to modify the path and the speed of a spacecraft, this technique allows to save propellent, reduce the cost and the time of the mission.

first attempt

In 1959, Soviet Union first attempted to use gravity assist with the probe Luna-3, which mission was to photograph the far side of the Moon.

Planetary Grand Tour

In 1962 Michael Minovich, a NASA’s mathematician, developed his own gravity assist technique, used by Gary Flandro to project his Planetary Grand Tour, a mission which target was to explore Jupiter, Saturn, Uranus, Neptune and Pluto taking advantage of their alignment, like a space highway. For the enormous cost of 1 billion of dollars, it was replaced by the mission Mariner Jupiter-Saturn, which became the Voyager program.

voyager 1

Voyager 1 used Jupiter's gravity assist in order to accelerate to reach Saturn, and then continue towards interstellar space. On the 5th of February the probe reached a distance of 158.9 astronomical units AU, otherwise 23 billion 784 million km from the Sun; this makes it the furthest artificial object from the Earth. Voyager 1 has been sending us data for 45 years, but it will stop within two years, until it runs out of energy.

How does the gravity assist work?

The probe must make a close fly-by of the planet and basically, it's a trade of kinetic energy between the two objects, due to their relative movement. According to the equation E=1/2mv², where E is the kinetic energy given by the planet and acquired by the probe, changing the mass of the planet with the mass of the probe, we obtain, expliciting the velocity v, that the planet loses a banal amount of speed, while the probe can gain up to twice the orbital speed of the planet.

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