The Juno spacecraft launched in August 2011. It coasted away from Earth and returned for a gravity assist flyby in October 2013. That flyby boosted the speed of Juno enabling it to coast away from the Sun and toward Jupiter. It arrives at Jupiter on the 4th of July at 9:30 CDT.
The trajectory brings Juno toward Jupiter over the north pole going 160,000 mph (257,000 km/h) . Its rocket will fire for about 35 min to slow it down in order to be captured in a highly eccentric polar orbit. Previous spacecraft have never visited Jupiter in this kind of orbit or this close. What will Juno encounter?
Juno is Huge
A human figure is shown next to the spacecraft. Three sets of solar panels extend out to capture the weaker light from the Sun. The diameter of the spacecraft is 66 ft (20 m). It is 15 ft (4.5 m) tall. It would take up as much space as a professional basketball court. Click to embiggen.
How Did Juno Get There?
This video illustrated the complex path taken by Juno. Our launch rockets are not powerful enough to give a spacecraft the speed needed to coast as far as Jupiter. The Sun pull them back before they reach that far. Juno was launched so it would return to Earth and transfer some of Earth’s momentum to the spacecraft. That gravitational assist gave it the necessary speed and direction. Watch as Earth orbits the Sun twice while waiting for the return flyby of Juno. No audio.
Details of Arrival Maneuvers
Juno must complete a series of choreographed maneuvers in a short time upon arrival. The transit time for radio communication is about 45 min one way. It must do these actions on its own. Video has no audio.
- Engine cover opens
- Thrusters orient Juno away from the Sun so the main engine can slow it down
- Thrusters spin Juno to a faster rotation rate
- Main engine fires about 35 min to slow the spacecraft for capture in orbit
- Thrusters spin Juno to a slower rotation rate
- Thrusters orient Juno back toward the Sun so the solar panels can function
Orbit of Juno
The highly eccentric orbit will be traveled at least 33 times according to the primary mission plan. Each orbit takes about 11 days and is perturbed somewhat from the previous orbit.
NASA
At closest approach, Juno is about 3000 miles from the cloud tops of Jupiter. This close approach brings Juno through intense radiation zones twice each orbit, here pictured in reds, yellows, and oranges.
NASA
Science Goals
Four and a half billion years ago our solar system formed from a collapsing cloud of dust and gas called a nebula. The Sun was first followed by Jupiter. It follows that Jupiter is composed of the same hydrogen and helium gases as the Sun. But, we don’t know much about the internal structure of the planet since it is shrouded in clouds. We can see the cloud tops as they rotate around the planet. Juno will pass close to those clouds. The instruments will penetrate deeply looking for structure and composition, giving us our best detailed analysis of them.
NASA
What is at the core of Jupiter? Is there a rocky core? Is it something more exotic such as metallic hydrogen? Juno should help give some insights into answers.
NASA
Radiation is a danger to the spacecraft. Jupiter’s magnetic field traps and energizes electrons to very high intensity. These can be harmful to electronics. So, they must be protected inside a special vault made of thick titanium. The dosage levels received by Juno will be equivalent to a human getting 100,000,000 dental x-rays in a year.
JunoCam
The public is invited to participate in this mission via JunoCam. Amateurs can upload their own ground based images of Jupiter. Plus, Juno has an imaging system. The public will have input and a vote on what targets to capture on Jupiter. You can see details and sign up at the link above.
How I See It 
Is it only taking pix? Measuring radiation? Measuring elements?
It is going to take pictures as long as the equipment holds up. It will be measuring radiation and magnetic fields very precisely. And, it will make measurements of elements and compounds in the clouds.
Here is a quote from the mission site.
“As the largest planet orbiting the sun, Jupiter has had a profound influence on the solar system. But its origin remains a profound mystery. To learn how Jupiter formed and how it has evolved, Juno will study the gas giant’s gravitational and magnetic fields, and explore the swirling clouds that form Jupiter’s colorful, trademark atmosphere. The spacecraft will also reveal what Jupiter is made of – and how much of it is water.”
It won’t collect samples. After a year of orbits, it will be slowed to dive into the clouds and disappear so it doesn’t contaminate any other bodies in orbit around Jupiter. Leave no trace is good policy.
I very much enjoyed your clear presentation of this, Jim. Having worked on spacecraft batteries myself I was curious about this latest design and found that it uses 55 Ahr lithium ion batteries. Most previous designs have used either nickel-hydrogen or radiation-powered sources, so this means that lithium ion chemistry is now considered reliable enough for the purpose.
I see great significance to Jupiter’s secrets because a gas giant’s presence in a solar system may well be crucial to the formation of a planet capable of sustaining life and protecting it from asteroid bombardment. If this is true, it should help in identifying other planets like Earth.
Thanks for your comments, Jim. Missions such as this take a long time to develop and carry out. The battery technology, and others, can never use what we currently use in today’s devices. As you know, they use what was available a the time of planning and building the craft. For Juno, it was launched in 2011. But, the technology is years older.
As these missions near their crucial time, I always get nervous. I want it all to work perfectly. We’ve had great successes lately. I hope this one continues the string. But, the path taken is a harsh one near Jupiter.
Nickel-hydrogen batteries were first used in a satellite in 1977 but it was at least a decade before they were accepted as reliable enough for general use. Before that, nickel-cadmium was used. In space, reliability is the name of the game.
This is pretty exciting. I wonder what they will find? An amazing technological feat and to precisely time the arrival for the 4th of July is over the top!
I think it is very exciting, too. I will be home to watch instead of going to fireworks. This is better in my mind.
Once in a lifetime vs. fireworks almost anytime. 🙂
I like Juno. I like the diagrams showing the elliptical orbits. Jim, is there anything truly “spherical” or “perfectly round” in space? I suppose there could be “spherical” or “circular” forms in space, but could they in reality be more ellipsoidal rather than round?
Your feeling about perfectly round is correct. It is rare. Maybe a dense neutron star or black hole is round if it isn’t spinning. Otherwise, they are distorted by their spin. Even Earth shows that to a small degree.
This is in the world of physics, but with math, geometry shows everything in second dimension, so there the ‘true’ circle exists. I guess physics defies all geometry, doesn’t it?
This really is fascinating. In the last photo, it looks like an avocado. If it had little tomato moons, we could have cosmic guacamole.
Seriously, what intrigues me most is that gravitational assist it got from the earth. And I laughed at this: “Each orbit takes about 11 days and is perturbed somewhat from the previous orbit.” When I was a kid, my dad used to say to me, “Don’t perturb your mother.” Now that I think about it, i did have the ability to pull her out of her ordinary orbit from time to time.
LOL…the biggest avocado I’ve ever seen.
I find the gravity assist orbits so elegant and graceful. Some missions have employed the technique multiple times. It is even used to slow down a craft and more safely approach the inner planets.
Our poor mothers and fathers. The job of kids is to perturb their world and see what happens.
Very fine post Jim. It must take a lot of calculations to pull off such a journey. Looking forward to the information Juno sends back. Take care. Bob
Did you know that in Latin the name Jupiter meant ‘Jove the father’?
I didn’t know that.
You can see the relationship between the second part of the compound and our Latin-derived word paternal. The Romans used the form Iup(p)iter primarily as a grammatical subject. In other cases, the ‘father’ part didn’t get added to the ‘Jove’ part.
Interesting and detailed post. Fingers crossed for a successful insertion of July 4.
Funny enough i have written about Juno in my latest post
https://thesciencegeek.org/2016/06/26/mission-juno/
I watched a NASA news briefing today. They are excited. But they know they are getting into some very hostile territory. Fingers are crossed all goes well.