juno approaching jupiter
NASA/JPL-Caltech

When it
pulled into orbit around Jupiter late on July 4, the Juno
spacecraft didn’t just make history for beating
a series of tricky scientific challenges.

It also secured a
Guinness World Record. Not bad for a Monday night!

Reaching Jupiter and getting into the giant planet’s orbit
required some complicated physics. In the process of executing
the necessary maneuver, the probe became the fastest spacecraft
ever, toppling a record that had stood for forty years.

At its peak speed, Juno was whizzing through space at 165,000
miles per hour. That’s thanks to the combination of its own
engine, the rocket launcher, and the gravitational pulls of Earth
and Jupiter. 

And that was actually just to sidle up to Jupiter, a high-speed
journey that still took five years.

Jupiter is 540 million
miles from Earth, but Juno’s journey was not a straight shot.
It looped around Earth on its way to its final destination,
using our
own planet’s gravity to propel itself toward Jupiter and
ultimately travelling a total of 1.7
billion miles. 

As NASA
explains: “During the Earth flyby, called a gravity assist,
Juno steals a tiny bit of [Earth’s] enormous momentum in its
orbit around the sun, giving the spacecraft enough energy to
… travel all the way to Jupiter.” Without that assist, it
could not have made it; the rocket that launched the
probe into space only gave it half the boost it needed.

Once the delicate dance of slipping into orbit started, the
spacecraft had to slow down again.

“When we approach Jupiter, we’re going way too fast to go into
orbit,” Rick Nybakken, the project manager for Juno, said

in a NASA video. “If we don’t do something, we’ll just fly
right by.”


First, it started spinning faster, five times every minute
instead of twice. The faster spin kept it more stable — think of
a child’s spinning top, which only tilts over when its spin
starts to slow down.

Then, Juno fired its engine for 35 minutes, but in reverse, so it
acted like a giant set of brakes, as
Space.com put it. The slower speed put it right in place for
Jupiter’s gravity to snag it into orbit, and about
20 minutes into the burn, Juno was orbiting Jupiter.

The previous spacecraft speed record was set on
April 17, 1976 by Helios 1 (and approached by
Helios 2). Each of these hit
150,000 miles per hour as they sank into orbit around the
sun.

Another mission to the sun, which NASA hopes to launch in 2018, would leave
Juno in the dust,
nearly tripling its top speed.

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