1. 
   Gravity assist
   Technique whereby a spacecraft takes angular momentum from a planet's solar orbit (or a satellite's orbit) to accelerate the spacecraft, or the reverse. See Chapter 4.
   Found op http://www.encyclo.co.uk/visitor-contributions.php
   
   
2. 
   Gravity assist
   In orbital mechanics and aerospace engineering, 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 a spacecraft, typically in order to save propellant, time, and expense. ...
   Found op http://en.wikipedia.org/wiki/Gravity_assist
   
   
3. 
   gravity assist
   Also known as the slingshot effect, an important spaceflight technique used successfully on a number of interplanetary missions, including Voyager, Galileo, and Cassini, whereby the gravitational field of a planet is used to increase the speed and alter the course of a spacecraft without the need to...
   Found op http://www.daviddarling.info/encyclopedia/G/gravityassist.html
   
   
4. 
   gravity-assist
   [n] - (spaceflight) a trajectory that passes close to a planetary body in order to gain energy from its gravitational field
   Found op http://www.webdictionary.co.uk/definition.php?query=gravity-assist
   
   

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