NASA's New Horizons probe is zooming past Jupiter to pick up
speed on its way to Pluto, becoming just the latest spacecraft
to get a slingshot boost from a planetary flyby. It won't be the
last. Mission planners are increasingly taking advantage of
celestial mechanics to speed up interplanetary trips. This year
is prime time for gravitational slingshotting: Just last Sunday,
the European Space Agency's Rosetta probe got a gravity assist
from Mars on its way to a comet encounter in 2014. New Horizons'
encounter, which reaches its climax on Wednesday, will speed the
probe toward a visit to Pluto in 2015. In June, NASA's Messenger
probe to Mercury gets a boost from Venus, while the Dawn probe
will be launched on a Mars-assisted mission to the asteroids
Ceres and Vesta. The reason for such assists is obvious: If a
well-chosen course through the planets saves on a spacecraft's
fuel requirements, that precious mass can instead be used for
things like a bigger rover or an extra camera. The gravity-
assist technique w