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Brazed assemblies will stand the test of Europe’s first mission to Mercury

01 May 2010

Europe’s first spacecraft mission to Mercury, which is expected to launch in 2014, will face many challenges, not least being the Sun’s gravitational field. Special thrusters are being developed here in the UK to ‘brake’ the craft against this pull and the construction of these ion propulsion units will require some particularly exotic joining techniques

Morgan Technical Ceramics (MTC) is supplying ceramic/metal assemblies for the solar-electric propulsion system used in BepiColombo, Europe’s first spacecraft mission to Mercury, which is expected to launch in 2014. The propulsion system, which is being manufactured by QinetiQ for the European Space Agency’s mission, uses brazed ceramic/metal assemblies to isolate components in the thrusters from extreme high voltage. Brazing is preferred over alternative methods of joining ceramic and metal, as it provides a more reliable and robust construction.

Mercury's distance to the Sun presents many technical challenges. The temperature can reach 470oC and solar radiation is ten times stronger on Mercury than on Earth. It will take six years for BepiColombo to reach the planet and a large amount of energy to ‘brake’ the spacecraft against the Sun's gravitational attraction will be required.

An advanced propulsion system is an essential requisite and to meet this technical challenge, QinetiQ has designed a solar-electric propulsion system comprising four T6 ion thrusters, each of which contains 17 brazed isolator assemblies.
 
The thrusters work at voltages of up to 1.85kV and are around ten times more efficient than chemical thrusters, which have traditionally been used to propel spacecraft. The ceramic/metal components provide essential electrical isolation between the propellant systems and the spacecraft, and are brazed into the feed pipeline using special Kovar expansion match fittings to produce a gas tight seal. MTC’s commercial manager, Yannick Galais takes up the story.

“We are extremely pleased to be working with QinetiQ on their largest space-related contract to date. There are many components and sub-assemblies within the thruster that operate at different voltages and need to be isolated from each other. Assemblies fitted with isolators that have been brazed to a threaded termination or flange result in stronger, rigid and more simplified joints.”

Brazed isolator assemblies are less complicated than alternative methods involving bolts, as these would require multiple isolators to isolate the bolts as well as the assemblies.

QinetiQ has worked with MTC on previous occasions and electric propulsion engineer, Mike Kelly says his company is confident in its brazing and manufacturing techniques. “We chose brazed isolator assemblies from Morgan Technical Ceramics for their robustness and ability to withstand the harsh environments,” he says. The components are a key technology in the solar-electric propulsion unit, which will not only make deep space missions possible for the first time, but also offer significant efficiencies to enhance future communication satellite operations.

Europe’s first spacecraft mission to Mercury, which is expected to launch in 2014, will face many challenges, not least being the Sun’s gravitational field. Special thrusters are being developed here in the UK to ‘brake’ the craft against this pull and the construction of these ion propulsion units will require some particularly exotic joining techniques
 


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