Brazed assemblies used in Europe’s first mission to Mercury

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 providing a much stronger and simpler solution compared to alternative methods of joining ceramic and metal resulting in a more reliable and robust system. Mercury's distance to the Sun presents many technical challenges. The temperature can reach 470°C and solar radiation is 10 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 pull is required. An advanced propulsion system is an essential part of meeting this technical challenge and QinetiQ has designed a solar-electric propulsion system comprising four T6 ion thrusters, each of which consists of 17 brazed isolator assemblies. The thrusters work at extremely high voltage of up to 1.85 kV and are around 10 times more efficient than chemical thrusters, which have traditionally been used as propulsion systems on spacecraft. The brazed components are used to electrically isolate the propellant systems and spacecraft from the high voltage that the thruster operates. The isolators are brazed into the feed pipeline using special Kovar expansion match fittings and they produce a gas tight seal. "We are extremely pleased to be working with QinetiQ on their largest space-related contract to date," says Yannick Galais, commercial manager, Morgan Technical Ceramics. "There are many components and sub-assemblies within the thruster that operate at different voltages and need to be isolated from each other. Fitting the assemblies with isolators that have been brazed to a threaded termination or flange results in a stronger, rigid and more simplified joint." Brazed isolator assemblies are less complicated than alternative methods, especially where parts need to be bolted together. Alternative assembly methods would require multiple isolators to isolate the bolt as well as the assemblies. "We chose brazed isolator assemblies from Morgan Technical Ceramics for their robustness and ability to withstand the harsh environments," says Mike Kelly, electric propulsion engineer, QinetiQ. "We are confident in its brazing and manufacturing techniques, having worked with Morgan previously." The components are a key technology in the solar-electric propulsion unit, which will make deep space missions possible for the first time and offer significant efficiencies to enhance future communication satellite operations.