Wire-to-wire bonding of μm-diameter aluminum wires for the Electric Solar Wind Sail

We present a novel ultrasonic wire-to-wire bonding method for bonding two micrometer-thick metal wires together. A special jig and an industrial wire bonder perform the bonding. This wire-to-wire bonding is the core unit process to produce space tether for the Electric Solar Wind Sail. The proposed method was validated experimentally with 38 bonds where a 25 μm and a 50 μm by diameter Al wires that were first bonded together after which the bond was pull tested. The measured average pull force was (74 ± 15) mN whereas the lowest pull force value was 40 mN. The results show that wire-to-wire bonds of sufficient strength can be produced for the Electric Solar Wind Sail tether application. Tether manufacturing was demonstrated with a separate test where a 1.4 m long tether was produced featuring more than 100 wire-to-wire bonds.