Juno rockets to Jupiter

Juno rockets to Jupiter and deputy principle investigator of the mission, Jack Connerney, explains to Graihagh Jackson why they called it Juno...

Jack - There was no fight over the name, and I'm not exactly sure where Juno originated but it was a very clever name for the proposal. It refers to the goddess or wife of Juno. Juno was, of course, guilty of straying a little bit in his marriage and apparently raised clouds to obscure his activities from his then wife the goddess Juno. She caught onto this very quickly and, using her special powers, she could see through the clouds and discover what Juno was up to... Lord knows he probably paid a dear price!

So the name Juno basically refers to that mythology and the ability to peer through the clouds and see what's going on inside Jupiter.

Graihagh - Tell me the story of the Juno mission. How and why was it dreamt up in the first place?

Jack - The Juno proposal was first put forward in the early part of this century. It really goes back in time to George Cisco's original study back in the mid-1980s. So even though we've been working on Juno for almost 15 years now, it really grew from a seed that was planted in the mid-1980s.

Graihagh - You must be pleased and proud that it's finally come into fruition?

Jack - Yes, it's been a long time coming!

...Laughter

Graihagh - Back to the mission at hand - given that it's been a bit of a slog to get off the ground, what is it about Jupiter that Jack and co are excited about finding out?

Jack - Jupiter is essentially the repository of what was left over after the formation of our Sun and it hold within it the secrets of solar system formation. And, of course, all the recent discoveries of planets around other stars has kind of given a rebirth to the whole idea that we need to understand how our solar system formed and the best way to do that is to go to Jupiter and understand its composition and its evolution, and so that's part of the wind in Juno's sails.

Graihagh - I wonder if you can just sort of paint me a picture of the journey from Earth, if you like, and what sort of death defying things it's had to do in order to make the mission possible I suppose?

Jack - Well let's see. We launched this spacecraft actually in August of 2011 from Cape Kennedy down in Florida, and I remember that well, it was a very, very hot down there. Then the spacecraft went out and ventured just beyond the asteroid belt and did a deep space maneuver that would target it for a rendezvous with Earth, and that flyby gave us a little bit of momentum to get us out to Jupiter in a very fuel efficient way.

It's kind of interesting the amount of spacecraft that we eventually will get into our 14 day orbit will weigh about 3,500 lbs. Before we did the burn to get into orbit, we weighed a little over 8,000 lbs.  And then looking back in August 2011, the amount of mass that we had to lift off the Earth to do that was about 1,250,000 lbs. So the majority of the spacecraft that we sent out there was actually fuel.

Graihagh - Wow! And what is it precisely that you're mapping - what is the data that you're expecting back?

Jack - Well there's a lot of instruments on this spacecraft; there's nine different science investigations and each investigation usually has a couple of instruments. So we record the magnetic field as we pass by the planet; that's the investigation that I lead and when we have built up a map of all these magnetic field observations we'll create a very detailed model of the magnetic field and see if we can't extrapolate that down into Jupiter to find out where it is generated and how a dynamo works.

We also carry another investigation called a microwave radiometer that looks at the radiation coming out of Jupiter. And by looking at that radiation as a function of the wavelength of the radiation and from where it originates, you can infer what the abundance of water an ammonia is in the atmosphere, and that's a very important element in trying to understand how Jupiter formed.

And we also do a gravity experiment and, of course, we do that by tracking the radio signals from the spacecraft and that tells us how the spacecraft orbit is perturbed by gravity.

All this goes into building a comprehensive model of Jupiter's interior and an evolutionary model of Jupiter from the time of it's birth 4½ billion years ago.

Graihagh - It sounds like a lot of information to take in, and send back, and also analyse and interpret. So when can we start expecting to hear about what you guys have found?

Jack - Well, so far I've only told you about half of it. Those three investigations are the ones that focus primarily on the interior. But we also have a very impressive complement of charged particle instruments: there's a waves experiment; we have a education public outreach camera; we have both an infrared and a ultraviolet imaging spectrograph.

The short answer would be that I'm sure that we'll see a lot of really interesting discoveries and results coming out almost immediately after a few of these orbits at the end of the year. While other science results will come out later when the mission has accumulated this dense net of observations, and that will take about a year and a half, I think.

Graihagh - Finally, I wonder if you could just tell me about the end of the mission - what's going to happen and when is that?

Jack - Ah well, the end of the mission is the interesting part! The nominal mission calls for 37 orbits. We are flying in a very hostile radiation environment, and radiation is not only bad for people, but it's bad for sensitive electronics.

So in order to protect the vital organs of the spacecraft, by which I mean the avionics and the instrument electronics, we put all of that stuff into a vault. It's a cube a metre on the side and its half inch of solid titanium, and that will reduce the radiation environment by a factor of almost a thousand. But even still, after 37 orbits, we will have accumulated quite a heavy dose of ionising radiation. Now we have a safety factor, a margin, that assures us that we should be able to operate the spacecraft and the instruments successfully for the 37 orbits. But NASA has a requirement and the requirement is that we do not contaminate the satellite Europa.

The non-emission plan has us performing this deorbit maneuver while we can still control the spacecraft. So there is another possibility that is under study now that would allow us to extend the mission lifetime by a few orbits at a time. And basically, the way that works is that as long as we control the spacecraft, we can put it into an orbit that we can demonstrate will decay into Jupiter over a series of n-orbits - you can pick any number n: 10, 20, whatever. And as long as you can command the spacecraft, you can keep kicking the can down the road. So, conceivably, we could get quite a few more orbits and more science return out of the mission in that way.