“It comes down to thermal properties and the balance between what heat the material absorbs versus how much it emits.” “It’s not obvious why we did that,” admits Draper.
But, given that titanium is also reflective, why go to the trouble of painting it black? The metal was chosen for its strength, flexibility and, crucially, its high melting point of 1,668C. The inner layers have a carbon fibre structure to hold the panel together, the outer ones are made of titanium foil. The final heatshield design is made up of a 40cm (16 inch) deep sandwich of between eight and 18 layers (the final number has not yet been finalised) with gaps between them – currently these are filled with air but eventually it will be just the near-nothingness of space. “The materials we use have to survive the environment but be light enough to be made into a structure that we can actually launch.” On top of that, the shield has to have apertures in the outer surface, with opening doors, to enable the instruments to see through to the star they are designed to study. The 3.1m-by-2.4m heatshield also needs to be light enough for a rocket to lift it off the ground, and it should be able to survive at least five years in space bombarded by everything the Sun throws at it. “The heat shield design has been driven primarily by materials – we had to ask what sort of materials do you need to use so the electronics don’t get baked?” “It’s been quite a challenge to do that,” admits Draper. To survive its close encounter, Solar Orbiter will have to cope with temperatures that are greater than 550C on the side observing the Sun and below -200C on the opposite side of the spacecraft, while keeping the electronics, instruments and propulsion system comfortable in between.
(Read more about the effects of this space weather in a previous story). Not only should it give us a better understanding of our nearest star but also the influence it has on the Earth and the vulnerable technology, such as satellites and power systems, we rely on.
The spacecraft is being designed to make a detailed study of the Sun and the high-energy particles it blasts across the Solar System. That is much closer to our nearest star than any previous mission, and well within the orbit of Mercury. Slated for launch in 2017, this probe will orbit the Sun at a distance of around 40 million kilometres (25 million miles). Just 1/20th of a millimetre thick, this animal-bone-coated titanium foil will make up the outer section of the heat shield being fitted to the European Space Agency’s (ESA) new Solar Orbiter spacecraft.
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