There are many ways of moving through the Universe – of
travelling from one point to another over great, even extraordinary distances.
There is also a way of using the world for your own ends: taking advantage of
slopes, winds, currents or gravitational fields, as fuel-efficient resources
for your own acceleration.
Gravity-assisted space travel is one such example, when a
spacecraft uses the gravitational pull of a nearby planet or other celestial
body to ‘slingshot’ itself toward another, more distant goal. Crucially, the
target or destination here is one that could not have been reached without this
assistance, not only in terms of the ship’s velocity but even in terms of its
original direction of travel.
You head toward one place to get to another – or,
channelling Hamlet, "by indirections find directions out."
Remarkably, this metaphorically rich idea of heading in one
direction to arrive somewhere else entirely connects gravitational slingshots
with the oceangoing people who settled remote island chains in the South
Pacific. These ancient mariners learned to use a combination of seasonal winds
and celestial navigation to push ever farther east, reaching the most extreme
outer edges of Polynesia.
