Designing Magnetometers for Space Missions Is Really Hard

​Working with a sensitive instrument to take critical scientific measurements about our universe is tricky enough; now put that instrument in the highly restricted confines of a planetary orbiter.

That's the challenge faced by Michele Dougherty, a professor of space physics at Imperial College London who was recently awarded a research professo​rship at the UK's Royal Society. Dougherty is the principal investigator for magnetometer instruments—which detect magnetic fields—on ​the Cassini mission to Saturn by NASA, the European Space Agency (ESA) and the Italian Space Agency (ASI), and on ESA's upco​ming JUICE mission to Jupiter's icy moons.

In 2008, Dougherty won the Royal Society's Hughes Medal for her work identifying the atmosphere around Saturn​'s moon Enceladus, and this year she was named one of the ​top 100 UK scientists by the Science Council.

She took a few minutes out amid an instrument crisis to explain more about what her work entails as the Cassini mission approaches its end and the JUICE mission is just getting started.

MOTHERBOARD: You're a professor of space physics and the principal investigator on two major magnetometer instruments. What does that mean—what do you do?
​Michele Dougherty: What I do depends on where we are as far as the mission is concerned—whether it's flying or whether it's still being built. On Cassini, I am responsible for making sure the science team produces the best science output we can from the data we're getting and at the moment I'm interacting a lot with the Cassini project because we're planning the end of the Cassini mission in 2017, when we're actually going to be flying very close to Saturn; we're going to be flying inside of the rings. This is completely unique. We haven't done it before and we probably aren't going to do it for a long time to come, because there aren't any future plans to go to Saturn.

All the instruments want to take data during those very close fly-bys and so at the moment we're all interacting with each other, talking about who will do what, when, and what's possible and what's not possible. On Cassini at the moment it's a mix of doing the science, making sure my team is doing the science, but also interacting with the Cassini project to make sure we get what we want at the end of the mission.

And you're also working on the JUICE project, I understand?
​Yes, that's right. That's in a completely different phase of the mission in the sense that we were recently selected to build the instrument and in fact the mission was officially adopted by the European Space Agency last week. So we've got the go-ahead to go full steam ahead and we've also just been confirmed to get the funding that we need from the UK Space Agency to actually build it.

There, what I spend a lot of my time doing is actually interacting with the European Space Agency, making sure that the instrument we're going to build has the power needs and mass needs to fit on the spacecraft; making sure that we're far enough away from the spacecraft so we're not affected by currents and fields that are generated on the spacecraft.

It's a very different interaction because we're still designing the instrument. I spend a lot of time with the engineers at Imperial talking about what we need to do to be able to design the instrument we need to be able to get the science that we hope to get once we actually go into orbit.

It's quite interesting for me because on Cassini I only became involved once it was actually flying. On JUICE it's very interesting to see it right from the start of the mission and see all the ideas. We've got to push back on the ESA engineers because they say to us, "No, you can't have that much mass, you can only have 100 grams less," and we turn around and say, "No, that's not possible; we can't build the instrument we need!" It's the first time I've been involved in that kind of interaction and it's very interesting to see how different it is to what I've been doing on Cassini.

What's the hardest part of working with these instruments?
​It's probably not best to describe it as "hard," but I think the trick is you need to keep your eye on the prize at the end, and the prize is the science. We were selected to build the instrument because we said we could—at Ganymede, the moon of Jupiter that we're going to orbit—measure the currents that flow in the ocean underneath the surface. To do that, we need to build an instrument that will allow us to do that.

We get pushed back a lot by the ESA engineers saying, "We can't give you all the things you need; what can you lose?" The trick is to keep your eye on the end goal, and that's to be able to do the science that we need—and to stand firm if you feel that what they're saying they can give you isn't sufficient.​

One of the things I'm most excited about is recently we managed to persuade ESA to allow us to have an additional sensor. When we first wrote the proposal for the instrument we said we wanted to fly three different types of sensors that would allow us to do our science, and when they chose us they said we could only fly two. We essentially spent a year persuading them that we need the third one and we recently got that back. It's a long, slow process, but you need to stay focused on what's important, and that's the science we get out at the end.

What sensor is that?
​We build fluxgate magnetometers, so we're going to build one, our German colleagues are building the second one, and the third one is a scalar sensor, which will be built by our colleagues in Austria. That one doesn't measure the vector, the three components of the vector field it only measures the strength of the field. By having all three sensors, it's essentially going to allow us to measure the very small changes in field that we need to be able to resolve the ocean currents.

Coming back to your own work, how did you get into this research in the first place?
​In a roundabout way. I was born in South Africa, I did my PhD and my undergraduate work there—I actually did my PhD in applied mathematics. I came over to Europe, I was in Germany for a couple of years at the Max Planck Institute and again I was working on more theoretical projects. It was only as I arrived at Imperial as a young postdoc 23 years ago now that I was asked if I wanted to spend a little time getting involved in a spacecraft mission that was going to fly past Jupiter.

There was a spacecraft called Ulysses that was going to use the gravitational kick of Jupiter to get it out of the equatorial plane and get it above and below the poles of the Sun. I was asked to put a magnetic field model together ready for that fly-by, and I spent a day a week working on that but it really enthused me, so I then moved to work on planetary science full-time. It wasn't something I planned, but I ended up doing it.

What's next for you now?
​Well, I'm very excited because I've just been awarded a Royal Society research fellowship, which means my salary is paid by the Royal Society so I don't have to do any teaching. That's giving me a lot more time to focus on the Cassini work and on the Jupiter work, but also it will give me time to do some science of my own. The last few years have been so busy, I've essentially done my science through my postdocs and my PhD students. I'm now really looking forward to doing some of my own. I've been told it's like falling off a bike; you get back on again. I certainly hope I'm going to find that's the case!

Which specific projects will you be working on there?
​It'll be both the Jupiter and Cassini work, but I'm really excited about the end of Cassini. We're going to get so close to Saturn, we're going to be able to understand where its internal planetary field is coming from, so that's what I'm going to be focusing on.

Amazing. I like forward to seeing the results.
​I really can't wait, it's going to be really exciting. We just need to convince the Cassini project we need to be able to take the data we need. We're getting there, but it's quite hard work because there are ten other instruments trying to take data at the same time, so we're trying to pick and choose who does what when.