Juno's mission is to study Jupiter, the largest planet in our solar system.
It's named after the Roman goddess who was Jupiter's wife. "In Greek and Roman mythology, Jupiter drew a veil of clouds around himself to hide his mischief. It was Jupiter's wife, the goddess Juno, who was able to peer through the clouds and reveal Jupiter's true nature," according to NASA.
The spacecraft set off from Earth in August 2011 and will have travelled 1,740 million miles by the time it reaches orbit around Jupiter.
Jupiter was only 445 million miles away from Earth when Juno set off (and is currently around 540 million miles away) but the spacecraft took a roundabout path to the gas giant so it could use Earth's gravity as a catapult.
Juno should begin to enter orbit around Jupiter at 4:18am BST on Tuesday 5th July.
After 5 years traveling to #Jupiter, @NASAJuno arrives today! This video shows a peek of its final approach: https://t.co/ysOKuGUWaQ
That's in the evening of 4th July for anyone in the US. A British-made engine will fire to slow down Juno enough for it to enter Jupiter's orbit. NASA engineers refer to this as the "orbit insertion burn".
The "orbit insertion burn" will last for 35 minutes and is the most crucial manoeuvre in the mission so far. If this goes wrong Juno will sail past Jupiter into the abyss of deep space, and it will all have been for nothing.
Once Juno is in orbit it will stay there for 20 months, flying round the gas giant 37 times in total.
To begin with, Juno will orbit Jupiter once every 53.5 days. Then, in October, the engine will fire again and propel it into a 14-day orbit for the main science part of its mission.
Scientists hope to find out how Jupiter formed and what's at its core, among other things.
Scientists are hoping to use Juno data to map the planet's magnetic and gravity fields and reveal information about its internal structure, as well as Jupiter's northern lights. They'll also be learning a lot more about what is in Jupiter's atmosphere, including how much water it contains – something the planet's radiation belts (seen above in an artists impression) prevent us doing from Earth.
