Heat Shield a Challenge for ESA's Solar Orbiter

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Space missions have not been much in the news these last few years, with the exception of the new Star Trek movie about to hit the streets. The problems, delays and more routine missions of the space shuttle have encouraged the public to assume space exploration will cease with the demise of the program in 2010. But in fact nothing could be further from the truth. NASA may appear to have lost its way but in other parts of the world programs still seek to boldly go where no man has gone before ” or if not then to send a robot in his place.

The Chinese are pouring billions into programs to build a space station. The country already has over 50 satellites in orbit and even talks of missions to the moon. India has been active in the satellite launch business for years with a proven track record and has aspirations to put a man in orbit. But in some ways the most ambitious continues to be the Europeans, driven more by a purest search for knowledge than nationalistic hubris. The Europeans have achieved a lot with their limited budgets and complex and often competing national bodies. Lacking the funds of NASA, Europe has launched many robotic missions and even after mixed results their aspirations continue with some ground breaking work. A project led by the European Space Agency (ESA) is expected to launch in 2015 and design work is well underway. The space craft known as the Solar Orbiter will travel more than 70 million miles to one of the least hospitable regions of our solar system, where temperatures are hot enough to melt metal. And, according to the Telegraph newspaper at least, the intense radiation along with chaotic magnetic fields can tear man-made structures apart. Scientists hope the missions will help them answer a long list of questions that still exist about the sun, including why its outer atmosphere is hotter than its surface, and what causes solar wind, sun spots and flares.

One of the biggest challenges will be how to keep the sensitive instruments inside the spacecraft cool enough to operate for the several years of planned operating life while still withstanding the intense heat on the sun-ward facing surfaces. The Orbiter is to travel to within 20 million miles of the sun, well within the orbit of Mercury and at an angle of 30% degrees to the equator so the craft can explore both the north and south poles of the sun. In an exchange with MetalMiner, Philippe Kletzkine, ESA project manager shared their latest ideas on how they intend to shield the craft from the relentless heat. The car sized Orbiter will feature a heat shield. But unlike re-entry heat shields on traditional spacecraft it cannot abate or shed mass to dissipate heat because it has to last for years rather than the mere minutes of an atmospheric re-entry. So ESA engineers have come up with a 16 thick heat shield composed of layers of metal (titanium and nickel alloys are the current front runners)  some mere microns in thickness, interspersed with gaps so that heat will be dissipated sideways into the vacuum of space. Mr Kletzkine said even though the front surface will be consistently at 1300 degrees F and have to withstand solar flux reaching 28 kW/m2 the delicate instruments inside the spacecraft will experience less heat than given out by an electric light bulb.

We expect the metals finally selected for the heat shield will not be decided until considerable further work is undertaken so expect a follow up from MetalMiner as we track this fascinating voyage of discovery in the future.

–Stuart Burns

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