How a gravity assist works

Tuesday, October 01, 2013

This is one of the clearest and most entertaining orbital mechanics-related posts I've ever read, and definitely one to bookmark if you ever think the subject will come up.

I only have one item to add to it:

Mission planners use gravity assists because they allow the objective to be accomplished with much less fuel (and hence with a much smaller, cheaper rocket) than would otherwise be required. Lifting extra fuel into orbit, just so it can be used later, is exponentially expensive. Furthermore, the extra speed gained by gravity assists dramatically reduces the duration of a mission to the outer planets.
The other reason of course for gravity assists: flying by other objects on the way to a mission gives us small extra missions for free. New Horizons' flyby of Jupiter provided us with images of its largest moons as well as the planet itself (that's Ganymede on the right). It just so happens that the best planet for gravity assists is also the largest one with the most moons, so any flyby of Jupiter is really a flyby of a (relatively) small system of its own. During this flyby the observations obtained were:
While at Jupiter, New Horizons' instruments made refined measurements of the orbits of Jupiter's inner moons, particularly Amalthea. The probe's cameras measured volcanoes on Io and studied all four Galilean moons in detail, as well as long-distance studies of the outer moons Himalia and Elara. Imaging of the Jovian system began on 4 Sep 2006. The craft also studied Jupiter's Little Red Spot and the planet's magnetosphere and tenuous ring system.


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