Science Interviews


Wed, 26th Feb 2014

Building a Mars Rover

Paul Meacham, Astrium

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Paul Meacham, a systems engineer working on the ExoMars Rover explains the A model of the ExoMars roverchallenges he faces when designing a robot which has to find new life on the red planet in 2018...

Chris - Paul you have the amazing party conversation starter of being able to say that you make rovers for far away planets.

Paul - Yes, although it tends to be the social equivalent of Marmite either it starts conversation or kills it dead. So, we have a 6-wheeled vehicle which we refer to as the Mars rover that's going to Mars in 2018. The goal of the mission is to look for signs of life outside our planet. So, whereas previous rovers and they primarily have been American, this is the first European one, have looked for the conditions for life and things like that. We are looking for life directly.

Chris - And what are the hallmarks of life that you'll be looking for?

Paul - Well, itís a little bit difficult to say because when you try and characterise life, you'll find itís actually very, very hard. So essentially, we have an organic molecule detector that looks for very simple molecular structures and we also have a drill on the front of rover that allows us to take samples from 2 meters below the surface.

Chris - like a Black and Decker.

Paul - Itís actually more akin to an oil rig actually in the way it works. It has a single drill piece and the extension rods that rotate into place to make a drill that is 2 meters long. And then the drill piece has a camera shutter in the bottom of it that can push the sample in and bring it back up to be analysed by the organic molecule analyser.

Chris - How big is this rover?

Paul - So, itís a medium size Mars rover if there's such a thing. Itís about 2 meters tall from the base of the wheels to the top of the mast and about 1.6 meters long. So, itís a reasonably sizable beast and that means it can travel over most of the terrain we expect it to encounter.

Chris - There seems to be a sort of vogue for describing your rover in relation to a vehicle here on Earth. Curiosity famously dubbed the size of a Mini Cooper. So, how big is your one then?

Paul - Well, weíre not quite that big. I guess weíre sort of the size ofÖ

Chris - Reliant Robin?

Paul - I was thinking more like one of those big lawn mowers that you sit around and drive around on. Itís kind of that sort of size I think.

Chris - So, how far down the development process are you with it?

Paul - Well, weíve got to the point where we are develop Ė well, we have several development models to test out the bits of the technology the rover will use that is less mature. Simply because it hasnít been done before. In particular, the autonomy the rover has, the ability the rover has to drive itself across the surface of Mars. We have several prototype rovers that allow us to demonstrate that and practice it, and see what works and what doesnít. But weíre actually some way from building the flight rover.

Chris - And you can recreate Mars to test it on, can you?

Paul - We can, yes. So, we have a big Mars yard, a giant sandpit if you like in Stevenage and the rover essentially practices in there. It drives over rocks. It sees how we handle slopes and our prototypes are deliberately developed such that they have the same weight on Earth as the real one is on Mars. So, they behave in the same way as a real one will do when it gets to Mars where the gravity is much lower. And therefore, we can write all our clever software to control it, knowing itíll work on the flight rover when we get there.

Chris - Is the temperature on Mars at night time not close to minus a hundred though?

Paul - It can be slightly lower than that. Yes, I mean, day time temperatures are around zero to 10 degrees which electronics typically like, but night time temperatures as you say can drop to minus 130 and they drop off very quickly because the Martian atmosphere is very thin and it just doesnít have the same heat retention capability that the Earth does.

Chris - But is it not quite good to have cold temperatures for electronics because doesnít the electrical resistance drop when itís nice and cold.

Paul - It can do, but the real problem is that essentially, when you get to the sort of below minus 100, you're starting to see your circuit boards is freezing, solder's going to start to break, even the circuit board will just break in two. And so, that means that itís now dead and youíve got no way of repairing it. So, we have to avoid low temperatures as much as possible.

Ginny - So, we have a little demo now to show you exactly what happens to various bits of electronics at very low temperatures.

Dave - So, what I have here is an exceedingly jury rigged circuit. I have some batteries with a little light and a very long coil of wire. In this thermos flask, I have some liquid nitrogen which is sitting a little bit colder than Mars at about minus 196 degrees centigrade.

Ginny - So, you can see. Weíve just poured some out into a cup and you can see that itís bubbling and that's because itís actually boiling in the same way that your kettle gets lots of bubbles in it when it boils, when it comes up to 100 degrees, this liquid nitrogen will boil at room temperature. All that vapour coming off is that kind of vapour as itís boiling. So, weíve got a nice little circuit here. Itís a little bit makeshift. Weíve got some wire and weíve got a bright red LED which everyone can see is glowing beautifully. So, what are you going to do with that LED?

Dave - So, the first thing I'm going to do is cool down the wire.

Ginny - So, you're popping the wire into the thermos flask full of liquid nitrogen. Weíve got beautiful vapour going everywhere and itís making quite a noise, and now it seems to have quietened down. So, what does that mean?

Dave - So now, the wire is sitting about minus 200 degrees centigrade and the wire actually is perfectly fine at this sort of temperature. If anything, LED will have got a little bit brighter because the resistance of copper drops an awful lot when you get down to this sort of temperature, I think even by a factor of 10. But if instead of that, we cool down the LED which is a piece of electronics. Itís does work quite so well.

Ginny - That looks so pretty. Itís glowing in the cup of liquid nitrogen and itís gone off. It stopped working. Have you just broken it?

Dave - If I take it out again and let it warm up slowly, it comes back on.

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