Building a Mars Rover

Paul Meacham explains the challenges he faces while working on building the ExoMars Rover...
26 February 2014

Interview with 

Paul Meacham, Astrium


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, it's a little bit difficult to say because when you try and characterise life, you'll find it's 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 - It's 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, it's a medium size Mars rover if there's such a thing. It's about 2 meters tall from the base of the wheels to the top of the mast and about 1.6 meters long. So, it's 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, we're not quite that big. I guess we're sort of the size of...

Chris - Reliant Robin?

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

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

Paul - Well, we've got to the point where we are develop - 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 hasn't 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 doesn't. But we're 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 it'll 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 doesn't have the same heat retention capability that the Earth does.

Chris - But is it not quite good to have cold temperatures for electronics because doesn't the electrical resistance drop when it's 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 it's now dead and you've 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. We've just poured some out into a cup and you can see that it's bubbling and that's because it's 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 it's boiling. So, we've got a nice little circuit here. It's a little bit makeshift. We've got some wire and we've 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. We've got beautiful vapour going everywhere and it's 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. It's does work quite so well.

Ginny - That looks so pretty. It's glowing in the cup of liquid nitrogen and it's 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.

Ginny - Yeah, so it's back. It's not quite as bright as it was at the beginning, but it's getting there. Yeah, I'd say it's just as bright. So, it wasn't that you broken it. It's just while it's that cold, it can't work. Why is that?

Dave - So, LED and most of the clever bits of electronics are made out of materials called semi-conductors and these can conduct or insulate and they can have all sorts of interesting properties. But in order to work they need a bit of heat to kind of give the electrons a bit of a kick and let them move around. But as you cool them down, the electrons kind of get locked up and can't flow as an electric current. They basically just stop working. So, if you get a piece of electronics cold enough, it just doesn't work.

Ginny - So, something to avoid on Mars I guess.

Paul - Definitely, yes. So, we have to manufacture the environment that the electronics sit in to be much closer to where the electronics do like to operate. So, somewhere between minus 40 and 10 degrees centigrade. The way we do that is, we put all the electronics in a central core structure which we refer to as the bathtub and the bath tub essentially has the space equivalent of double glazing. So, it has an inner skin and then a cold gas trapped between that layer and the outer skin. Just like double glazing, it stops the heat from escaping and creates a thermal barrier. So, you can control the temperature of the inside of that bath tub to whatever you like. Typically, somewhere between minus 40 and 10 degrees.

Chris - Where does the power come from?

Paul - Well, all our power comes from the solar panels that sit on top of the bathtub and essentially seal it. So, that's our primary power source while we're on Mars. We have a battery as well that charges up in the day to keep the rover alive at night. But in essence, yes, we are completely environmentally friendly and solar powered.

Chris - These solar panels, how long will they keep the rover running for?

Paul - It's an interesting question because one of the big issues with using solar panels on Mars is that they eventually get covered in dust. It's very, very difficult to get that dust off once it's landed on the solar panel. Essentially, your efficiency, the amount of power you're generating from that solar panel drops off over the mission.

Chris - You need a robot to clean them.

Paul - Almost, but then that can get a little bit difficult because you end up scratching the glass because the solar panel is covered in glass and then you have permanent damage, and then you will never generate enough power again. So, it is a problem and we oversize the solar panel to compensate for a bit of that. But fortunately, dust storms which can envelop the whole planet on Mars are seasonal. They tend to happen from the autumn equinox around to the spring equinox. And so, it makes sense that our mission lands at the spring equinox, just after the dust storm season has finished and then our nominal mission should be completed by the time it starts again.

Chris - Questions from the audience. Who would like to ask about building a robot to explore another planet?

Mark - Hi. It's Mark from Cambridge. I was just wondering, given that what can go wrong will go wrong and that Mars is a long way away, do you tend to over engineer the systems to try and ensure that they don't break or does the rover have some ability of repairing itself at all?

Paul - Certainly, we do over engineer it a little bit to guarantee that it's going to work over its nominal mission. But in fact, the main way we avoid problems is to carry two of everything. We have a prime and a redundant equivalent of every single unit on the rovers. So we have two computers, two power distribution units, two sets of sensors, and so on and so on. So essentially, if one breaks you switch on to the B side if you like, and use that instead and they both work in the same way.

Chris - Have you got any spare tyres?

Paul - Actually, we don't use tyres because they're made of rubber and we can't organics to Mars if we're looking for life. So, we actually make the wheels of the rover out of metal and they are sort of like a spring in a wheel. They compress slightly to allow us to climb over rocks and grip properly.

Chris - How do you actually control and steer the rover around on Mars?

Paul - Well, because Mars is so far away and in the worst case, there's a 20-minute time delay. It's not practical to drive the rover by remote control. Even though it's monitored back on Earth, we actually want the rover to make as much of the decisions as it possibly can. In fact, our rover is capable of accepting a target which can be several hundred meters away and is simply a X, Y coordinate and then the rover does everything else itself. It will use its cameras to image the terrain in front of it, identify where the rocks and the slopes are, figure out if certain areas of that terrain are safe or not, plan a path through it and then drive that path all by itself. In fact we'll only see the rover once or twice a day.

Chris - I'm still disappointed that you can't sit in your lab with like a radio control device and sort of think, I'm steering this thing. How far away is it to Mars? How far is your message having to go to get to Mars?

Paul - It varies. So, the closest approach is 36 million miles. The furthest is 250 million miles. So, that's where the 20-minute time delay comes from, even travelling at the speed of light.

Chris - So, 20 minutes for my message to go what I want it to do to get to the rover.

Paul - Yes, that's right. So, if the rover was driving forward and you saw an obstacle you wanted it to avoid, you'd press stop and then 20 minutes later, it would have hit whatever the obstacle was you were trying to avoid because the signal takes so long to get there.

Chris - Any other questions so far? One just at the back, this lady...

Sophia - Hello. I'm Sophia from Cambridge. I would like to know if this rover stays on Mars or do you bring it back?

Paul - Sadly, no. It's staying on Mars forever. The reason for this is quite simple. When you want to take lots of scientific instruments, you want to essentially have as big a rover as you can possibly send, and if you want to bring something back, you have to take the fuel with you to then launch it back off the surface of Mars and back to Earth. And of course, that severely limits the size of the rover, the number of scientific instruments, and so on that you can send. So, it's so simple choice essentially. Do you want to do lots of science or do you want to get the sample back? To this point, all the rovers have been on a one-way trip, but the mission that follows ExoMars is called Mars Sample Return and it's a much simpler spacecraft. It's designed to land, take some samples, and then get back up and back to Earth. But the groundwork has been done by the rovers because they had figured out by travelling large distances, where is interesting and where is not to take samples from.

Chris -  What about making sure we don't bring back something horrible to Earth from Mars? What steps are in place to make sure we don't ruin our planet?

Paul - It's a big issue. It applies in both directions actually. We have somthing called planetary protection that means we can't contaminate Mars. But yes, if we were going to bring a sample back, it can't contaminate the Earth. So, it's likely that the sample container would be essentially launched and then collected in orbit by another spacecraft that has not been down to the surface of Mars. That would then return it back to Earth and it would be sealed in an entry vehicle to get it back down to the surface. So, no part of a spacecraft that has been exposed to the Mars environment has actually been exposed then to Earth.

Chris - So that way, there's no way it can deposit anything into Earth's atmosphere.

Paul - That's right and you'd have about 10 minutes or so on landing to go and find it, collect it, and get it back into a clean environment.

Chris - Before someone else nicks it or...

Paul - Well hopefully not - because of the risk of contamination still.

Chris - Any other questions? Yes, Neil. Go ahead.

Neil - What is the lifetime of a rover on Mars?

Paul - Well, the nominal mission if I can call it that is 218 days or sols as they are on Mars, and that's reasonably typical, the Spirit and Opportunity rovers had a lifetime of 180 sols. Curiosity is about 2 years. So, that's when it has to achieve all its basic science goals. But of course, the mission can go on and will go on beyond that. Partly as a result of the over engineering, but partly because we'll just keep running it until something breaks.

Ginny - Steve on Facebook wants to know, "We've got driver-less trains and you were talking about a sort of driver-less rover, so when are we going to have driver-less cars, and would we really trust them? Can we be sure that they'd actually be safe?"

Paul - It's an interesting question. I mean, we are starting to make steps to that. Google have a car that can do some degree of driving by itself. It's probably only ever going to work if all the cars are driver-less because then there's less unpredictability certainly. But I mean, certain features of it are appearing in cars these days like lane control. So, if you start to go outside of your lane, it'll vibrate to let you know that's happening. So, some features will come in to our cars, but I think we're some way from all of us driving cars that are autonomous.

Chris - Any other questions from you guys out there, one at the back just over here?

Rhys - So, this is Rhys Edmunds from Comberton. How long roughly will a rover be out on the surface of Mars per day?

Paul - Well certainly at night, we don't go anywhere The rover is parked up at night because of the temperature drop, just to keep the rover alive. But in the day, it rather depends on whether we're at the science site or not. So, it might be drilling holes or we might be doing analysis, that sort of thing. But if it's a driving day, we expect to travel about 70 meters and that's all being done autonomously. Over that 218 days, we'll be doing about 4 km or so. So obviously, we're not driving every day, but that's typically what we have to design for.

Chris - When will this actually blast off heading for Mars?

Paul - We're due for launch in 2018 and the launch date is quite specific because you can't just go to Mars whenever you like.We have to wait for the planets to be in the correct alignment relative to each other, such that by the time you blast off and get to Mars orbit, Mars is there. So, that only happens every 2 and a bit years and that's why the first part of the mission goes in 2016 and the rover goes in 2018 because they have to wait for the next opportunity.

Chris - Curiosity came down in this incredible way where they actually had a platform that had thrusters that stopped the rover above the surface and then winched it down onto the surface of Mars. I mean, it was incredibly elegant. How are you going to land? Not like a Beagle hopefully.

Paul - Hopefully, not. But we will also be using powered decent because that's really the standard for rovers of this size. Partly because you want to have a nice gentle landing, but partly because you want to target the rover very, very carefully. I mean now, we have a reasonable idea of where we want to take samples. The rover has to be able to be directed to that place and can't just bounce around for miles. So, we essentially have a landing platform that has rocket motors in it, but the difference is, we're sat on top of it, not being winched down from it. We land the whole thing because the difference between us and the Curiosity mission is that we have instruments and so on, on the actual landing platform. So, we want to land them both in the same place, so we get a consistent data.

Kate - I'm Kate from Cambridge. I've got a question. How would the Mars rover have done on Robot Wars and does the panel think that more kids would get into robotics if the BBC brought it back? How else should kids get into robotics?

Paul - I don't think our rover would fair very well because it's very, very slow. There are rather different constraints when you are 250 million miles away. So actually, we would be severely outcassed I think on the Robot Wars arena. But yes, you're absolutely right. That sort of thing is a great inspiration for young people to go and explore engineering software. Something like a rover has so many different aspects of engineering that it's actually quite a good way to explore lots of different areas.

Ginny - Neil, do you think one of your arms would do quite well? Would it be able to sort of punch people?

Chris - In Robot Wars?

Ginny - In Robot Wars, yeah.

Neil - Quite possibly. I think it would do quite well. I always...

Chris - Pipette the opposition to death...

Neil - Yeah. When I was younger, I always fancied entering the competition. Maybe I'm not too old.

Ginny - Now, I've got a sort of more general question for all of you I guess is, Maybeline on twitter wants to know, could we power robots on something other than, well, I guess we use electricity. Could we use something like food to power robots?

Paul- Well, I can start by saying something which is quite important for planetary exploration of the future, particularly when we go so far away from outside the orbit of Mars where solar power is starting to become not a viable source. It may even be applicable for human missions, particularly with regards to getting something back without having to take lots of fuel with you to do that. One of the ideas is that you would actually mine methane and use that as your fuel to power your rocket or whatever to get back to Earth.

Neil - It's really a fracking mission.

Chris - Is that what the drill's for?

Paul - Not in this case, but...

Chris - Any other questions from everyone at home?

Ginny - So, Joe asks, "There's been this movie out recently 'Her'. I haven't seen it but I think it's about someone falling in love with one of the sort of voice recognition systems and we were wondering how important is it to have an emotional connection to a robot and sort of linked to that. What do you need to have that emotional connection? Do we need something that looks human, that sounds human?

Blaise - Yeah. I think it's actually very important. People like using robots that have more emotion. In some ways, that's possibly why people have been more interested in Siri which is from Apple then from Google's product which is called Google Now.  Because Siri has this kind of personality and you can ask it if Siri will marry you for example and...

Chris - What will she say?

Neil - I think usually, she says, no.

Chris - She's fussy then.

Neil - She's very fussy and I think has refused most of the population. I think she likes her own company. So, I think the things that we get affected by, are things like the voice. It's quite easy for us to hear emotion in a voice and that can have a very big impact. So, I think the more that you have, the more affinity you can attach to the robot. But I think it's not necessary that you have everything. So, you probably don't even need to have a face or a picture of a face. You can start developing some emotion for your robot/device even if it doesn't have a picture of it.

Chris - Do you give your robots names, Neil?

Neil - Yes, we do. For the projects, they'll all have names and they've had various themes of names over the years.

Chris - The diagnostic lab I work in, they've got things like Rob, Jane and Freddie and stuff like that. I mean, Scooby Doo. Everyone thinks it's quite funny, but it does actually kind of endear the staff to the machine they're using to do all these tests.

Neil - Yup and we've wasted many hours debating what we should call the systems in our robots.

Chris - And?

Neil - The debates continue.

Chris - Have you got a nickname for your robot, Paul?

Paul - Yeah, all the prototypes have names. So, we've got Brigitte, Bradley, Bruno, and Brian, are our four.

Chris - So, you favour B's then.

Paul - We do, yes. So, it started with Brigitte because our prototypes are referred to as bread boards, it's the correct engineering term for them. So they often get shortened to BB in the documentation. One of the members of the project team was a fan of Brigitte Bardot and so, it became known as Brigitte and we sort of followed on with the B's from there.

Ginny - That kind of leads on to - there's a question here from Jenny Lugo who wants to know if there are any sort of ethical issues around the use of robots and she quotes this article she read which had the line, "We had people interact with very cute baby robotic dinosaurs and then at the end of the workshop, we asked them to torture and kill them. They were pretty distressed by this."

Chris - I'm not surprised.

Ginny - So, does naming your robots and sort of giving them a personality, then mean you're going to be sad when they break or are you going to miss your robot that doesn't come back from Mars?

Paul - Yeah, I guess so. There's a very sad cartoon that does its rounds on the internet of Spirit asking whether it can come home or not, but yeah, it gives them a bit of a personality. And they do have personalities and it probably makes us care for them, I think.

Chris - The Chinese lander that was exploring the moon across the Christmas period developed a problem and it sent back a message and it said, "My masters can't manage to shut me down in time for the cold weather that's coming, so I might not wake up again in the morning. Goodbye." It got virally tweeted around the world because I think everyone felt very attached to this machine. Did people get attached to your lab machines?

Neil - I think attached is a strong word, but yeah, if you've been working on a system, on a robot for a year and you know it's a prototype, and at some point, it's going to go in the skip then you think you've put so much effort into making something and then once it's served its purpose to throw it away, that's sometimes tough.


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