What would a successful Europa mission look like?

What might determine the success of NASA's Europa Clipper project? And how is the Europa mission pushing the limits of what we are able to do in space? John Zarnecki is professor of space science at The Open University, and a former director of the International Space Science Institute. We first met many moons ago when he visited Cambridge University to talk about his involvement in the Cassini-Huygens mission, which put a probe on Saturn’s largest Moon, Titan. I began by asking him how that mission 20 years ago differed from this one…

John - It's different. It's not trying to land, but it's a very challenging environment because Jupiter is one of the worst places in the solar system from the point of view of radiation. It's coming from the very strong magnetic field around Jupiter, the magnetosphere. And in that strong field, particles, electrons, other charged particles, get accelerated to, to very high energies. And these then smash into your delicate instruments. So what Clipper is going to do is to go into an orbit, which means that for a lot of the time, it'll be quite a long way outside of the damaging regions. And it will then dive in and pass relatively close to Europa, take its measurements and then go back out on its orbit.

Chris - How can you simulate what it's going to experience on its way to a place like Saturn in your case, but Jupiter in this case, so that you can give it a trial run before you actually have to put this thing in space. Because if you are building it once, you've only got one go <laugh>, if it's going to take seven years to get there, you've got one chance. How do you make sure it's as foolproof as it can be? Do you literally dunk these things in liquid nitrogen to see how they handle cold temperatures? Do you blitz them with radiation in the lab to see how they handle that sort of thing? How do you do that? How will this team have approached safeguarding that aspect of the Europa mission?

John - Well, Chris, it sounds as if you're a rocket scientist already because we do exactly what you've said. In fact, there are two types of approaches one takes. One is physical testing, for example, what we call thermal vacuum. So we put the instrument, or in fact the whole spacecraft in a big vacuum chamber and we expose it to the extremes of temperature that it's going to see. In fact, we overtest it. So we go hotter and colder than it will actually see. We will shake the spacecraft. That's a horrible test. When you see your delicate instrument, you see it being shaken mercilessly. That's to simulate what happens on launch. You often do an acoustic test because also at launch there's an enormous level of sound which can be very damaging to equipment. The other thing that you do, and this is increasingly so, you run computer models. So a good example of that is what's called thermal modelling. In a computer you can expose your equipment, your materials and the structure to extremes of temperature. But it's really a combination of the two approaches.

Chris - And assuming all that goes to plan and you get to where you are going, in this case we're hoping for Europa in six years time, for this mission. To what extent is the mission baked in from that point? You have to follow a specific research programme. And to what extent will they have the flexibility to adapt the mission once unforeseen things happen, other exciting things present themselves. Because that's what we're in the business of doing science for, isn't it? Because there will be things that are uncovered that then lead you down a rabbit hole that you hadn't foreseen.

John - Absolutely. So the mission, to a degree, is planned out already. When we arrive at Jupiter, that will be the expectation, but you can be almost certain that things will happen. So there'll almost certainly be some technical aspects that won't work quite right. And this is where another aspect of the design will come in, and that is redundancy. So some physical aspects of the spacecraft, for example, transmitters, they're probably doubled up. So if one fails, you can switch to another. But there might also be good things that happen. By that I mean some particularly exciting feature might be found that we hadn't known about and which might, for example, give us access or the possibility of accessing material from the subsurface ocean. So that will mean a change to the orbit to access that region. Having said that, at least initially, my experience is that all the mission operations people, they're very conservative in their approach. And so certainly early on they will minimise any risks taken. But you can be pretty sure that as the mission evolves and they become more confident of the spacecraft, how it operates, that they'll be prepared to take more risks. And the real exciting part comes towards the end of the mission. I would be very surprised if in the last few passes of Europa, they don't go for a very, very close flyby. And if something goes wrong with the targeting, there's a possibility of crashing into the surface. But you know, as the mission goes on, certainly greater risks will be taken.

Chris - We'll actually end up with two probes in the Jovian system, won't we? Because we'll have the clipper mission, which is the one that's just blasted off. We'll also have the other one JUICE. So we'll actually have a pair of probes there. Does that offer any opportunities? Can one thing inform what the other one then does?

John - Yes, there's absolutely no doubt about that. So JUICE, that's an ESA mission, European Space Agency mission, which was launched last year. And they are going to be in the Jovian system at the same time. But the emphasis of JUICE is on the moon Ganymede. So Ganymede is the largest of Jupiter's moons. In fact, it's the largest moon in the solar system. The belief is that it also has a subsurface ocean. So I mean, to me, I think the fact that these two missions are going demonstrates that the scientific emphasis in the study of the outer solar system has shifted in the last 20 years towards the study of these icy moons about Jupiter and Saturn, rather than the massive planets Jupiter and Saturn themselves.

Chris - What does success for you, given your pedigree and form in this area, what does success of this mission look like to you?

John - Both of these missions have the potential to, I would say, confirm beyond reasonable doubt that these oceans absolutely do exist. So success would be if we get incontrovertible proof from Ganymede or Europa or perhaps both, that we really do have these oceans below the surface. And then of course we can start thinking of 20, 30 years hence, of sending a mission which somehow can get down below that ice and into the liquid.

Chris - Well, you're sort of retired these days. You've got some time on your hands, John?

John - <laugh>. Well, I've said to you before, Chris, rocket science is great, but it is, I would say, mostly for the youngsters because it just takes you over. You know, it's body and soul 24/7. So I think it's the youngsters turn to burrow below the ice and get into the oceans. I'll be watching though, from afar.