Katie Hassell, Airbus Defence and Space
The Solar Orbiter, a joint project between NASA and the European Space Agency to study the Sun close up, is scheduled for launch in 2018. It will get nearer to the Sun than weíve ever been before. Airbus Defence and Space were awarded the contract to build the Solar Orbiter, and so they have quite a challenge on their hands protecting it from the Sunís intense rays. Katie Hassell is a Senior Spacecraft Thermal Engineer with Airbus she explained to Connie Orbach just how close to the sun the probe will be going...
Katie - Solar Orbiter, as part of its mission, will going to a third of the distance from the Sun to the Earth, so the close third to the Sun - thatís just inside Venusís orbit.
Connie - And what sort of temperatures is that then - thatís a lot closer than we are?
Katie - Yes. So it has a really big heatshield on the front of the spacecraft and the front of that heatshield will see around 600 degrees. As an idea, if youíve ever left a bar of chocolate in your pocket for a bit too longÖ it will do that to aluminium.
Connie - Thatís the front but the back must be quite a different temperature?
Katie - Yes, the back is cold. So the idea with the heatshield is that it works a little bit like a parasol in the sense it provides a shadow for the whole of the spacecraft and so, everything behind that heatshield is going to be cold. And it can see dark space which we model that around -270 degrees, so the spacecraft itself could get down to temperatures of about -180.
Connie - Wow!. Thatís a really huge range.
Katie - Yes.
Connie - And Iím guessing, if weíve not got the atmosphere of the Earth, then Iím guessing thereís a radiation issue as well?
Katie - So radiation is an issue, particularly for Solar Orbiter, because itís going so close to the Sun it does mean thereís going to be a lot of charged particles in the environment that itís going to be in.
Connie - When youíre thinking about these problems, this huge range in temperature, lots of radiation, how do you go about choosing the materials to make the Solar Orbiter from to deal with these conditions?
Katie - So we have a good idea of how certain materials behave. We know radiationís going to be an issue, which then starts to narrow down what type of materials we can use. So for Solar Orbiter, weíre looking for anything that is electrically conductive, so anything that isnít electrically conductive we then basically remove that from the options - itís not available to us.
Connie - Why does it need to be electrically conductive?
Katie - Thatís these charged particles. We donít want static to build up on any part of the spacecraft because, otherwise, we could end up with electrostatic discharge; itís like little lightning across the whole spacecraft, and that can damage the instruments.
Connie - And so what about the other problems, the other materials?
Katie - So then, after that, it becomes quite a lot of a thermal issue. So what weíre looking to do there is maintain the temperature of the spacecraft. Ideally, from a thermal point of view, it would be lovely if the spacecraft could be white. However, we couldnít find a white material that was going to maintain its whiteness during the lifetime of the mission so weíre actually going to be using black, and by doing that it means that we can understand a lot more how the colour of the spacecraft is going to change over its lifetime. And the idea is we try to maintain a particular type of colour so that weíre controlling the heat flow so from Sun, around the spacecraft, and then out to space.
Connie - So you kind of know whatís going to happen right from the beginning as opposed toÖ?
Katie - Thatís the general idea.
Connie - OK. What are the materials then - what sort of things are you using?
Katie - Inside that shadow cone, weíve got thermal blankets on there, theyíre a little bit like what you might see marathon runners being wrapped up in, but lots of layers of those. They're made out of aluminium foils and, again, theyíve got a black coating on the outside of those. And then the heatshield that Iíve already mentioned, that has a special paint on the very front of it that, it just so happens, is made out of burnt animal bones.
Connie - Ohh - that's quite surprising!
Katie - Kind of a random one!
Connie - Yes. Thereís a load of burnt animal bones going up into space?
Katie - Yes.
Connie - Why? Surely there's lots of things you could make which would do the job?
Katie - Weíve asked for a black paint that can meet all of our requirements and it just so happens that the black paint that has come back to us, that can maintain all of that electrostatic discharge, that can maintain itís colour, and isnít going to fall off once itís all painted on there, itís made out of charred animal bones.
Connie - OK so, basically, this kind of a big box and itís got this big square sunshield in front of it, which isnít made of aluminium - whatís it made of?
Katie - Itís made out of titanium.
Connie - OK. Made of titanium and covered in this black paint made of all thingsÖ crushed animal bones. So how do you know itís actually going to work?
Katie - Good question!. During the whole development of the mission we do a lot of analysis, so different teams do their own types of analysis. Iím a thermal engineer so Iíve been doing thermal analysis. And then what we do is we build it and we put it in whatís called a solar simulation chamber and that is, essentially, a really big box that has a zena light bulb. And the xenon light bulb is to simulate all of the different wavelengths that the Sun emits its light in, and we put our spacecraft in there and we see how the spacecraft reacts to that sunlight.
Connie - So that xenon light bulb is like a mini-sun?
Katie - Itís a mini-sun, yes.
Connie - Oh Wow! And thatís just looking at it right in the here and now. Iím guessing you have to then do some sort of analysis on this?
Katie - Yes, we do more analysis at that point. So we make a model of the test chamber and what we do with our spacecraft model is we make sure that the temperatures on the model match what weíre getting out of the test chamber, and then we run lots of simulations to model the different types of environments that the spacecraftís going to be in during its mission lifetime.
Connie - And how long is that mission lifetime - how long is it going out there for?
Katie - It works out at around nine years. Itís got three years where itís actually going to get to the Sun, and then weíve got three years where itís doing the science and then, all being well, it will have a further three years doing even more science.