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# 4 Numerical Fun Facts About the Juno Spacecraft

Did you hear the exciting news that NASA just successfully put the Juno spacecraft into orbit around Jupiter? Want to learn 4 super-cool numerical fun facts about this mission? Then keep on reading!

By
Jason Marshall, PhD,
July 9, 2016
Episode #284

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July 4th was a day of celebration in the United States this year. Of course, that day is always a big deal in the U.S. (something about something that happened 240 years ago), but this year, the Fourth was especially special.

In fact, it wasn’t just an exciting day for the U.S.- it was a day for humans around the world to celebrate. Because this past July 4th, humanity successfully put its newest spacecraft into orbit around the planet Jupiter.

And, most importantly for us, it was also a day for math fans to celebrate, because this NASA mission to Jupiter is full of awesome numerical fun facts for us to talk about. How big is the spacecraft? How much energy does it use to operate? How far is it from Earth? And how much did it cost to send it there? Let’s find out!

## Fun Fact 1: How Big Is Juno?

The folks at NASA dubbed the spacecraft "Juno" because that’s the name of the wife (and, interestingly, the sister) of Jupiter—who is the “Zeus” of classical Roman mythology. The spacecraft version of Juno is going to spend the next (and last) 20 months of its life orbiting Jupiter and keeping an ever-watchful eye on the planet and its four Galilean moons—Io, Europa, Callisto, and Ganymede, the mythical versions of which all had, shall we say, complex relationships with the king of the gods.

Anyway, enough about the mythological origins of this mission’s nomenclature; let’s turn our attention to the Juno spacecraft itself. In particular, let’s talk about its size—because it’s BIG. The spacecraft is comprised of a roughly cylindrical central satellite surrounded by a trio of nearly 10-meter (or about 30-foot) long spokes tiled with solar panels. That means the spacecraft is on the order of 20 meters across (about 60 feet), which is bigger than an NBA basketball court!

## Fun Fact 2: How Much Energy Does Juno Need?

For comparison, the New Horizons spacecraft that travelled to Pluto and beyond last year is “merely” the size of a grand piano. So why is Juno so big?

Well, unlike every previous outer solar system mission, Juno is not nuclear powered. Instead, it’s entirely powered by the Sun - which means that Juno needs those large solar panels to absorb as much sunlight as possible, so that it has power to operate its scientific instruments, radios, and flight control systems, as well as keep itself warm (because space is really cold that far from the Sun.)

The distance between Jupiter and the Sun is five times the typical distance between the Earth and the Sun, which means that Jupiter only receives 1/25 as much sunlight per unit area as we do here on Earth. So the solar arrays need to be 25 times larger than they would be if the spacecraft were orbiting the Earth.

And how much energy do those huge solar arrays collect for Juno? Around 500 watts, which isn’t a lot—it’s only enough to light-up five old-fashioned 100 watt light bulbs. Which means not only is Juno a big spacecraft, it’s an amazingly power-efficient spacecraft, too.

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