AbstractsPhysics

Tethers are key elements in the electric solar wind sail (E-sail). In this thesis I claim that E-sail tether manufacturing on km scale is possible. The E-sail is a space propulsion method for interplanetary missions. It uses long, thin and conductive, tethers to create thrust from the solar wind. Based on simulations a full scale E-sail using one hundred 20 km long tethers could create a continuous 1 N thrust. Compared to state of the art ion engines the proposed E-sail produces 10 100 times more specific impulse over the device lifetime. The E-sail is estimated to lower costs of interplanetary missions by reducing the payload mass needed to launch to orbit and by shortening the travel time. Manufacturing is an important technical challenge to the E-sail. A multifilament tether structure is needed to provide micrometeoroid tolerance to the tether. To address the challenge we combined an industrial ultrasonic wire bonder and a custom-built tether factory for tether production. A customized 3-wire bonding wedge enabled 4-wire multifilament tether manufacturing. The tether comprises 25 and 50 µm in diameter (Ø) aluminum wires that are ultrasonically welded together. The main result of this thesis is that we showed the feasibility of large-scale device manufacture by producing a continuous 1.04 km long multifilament tether comprising 90 704 wire-to-wire bonds. The measured bonding yield of the manufacture was 99.9%. Wire-to-wire bond pull strength was measured in a separate test on a 97 m long tether produced subsequent to the 1 km tether production. The maximum sustainable pull force of the tether bonds should exceed the estimated 50 mN centrifugal force of the spinning full scale E-sail. The measured average maximum sustainable pull force of 252 bonds along the 97 m test tether was (99 ± 8) mN with a minimum recorded value of 80 mN. This result shows that E-sail tether production on km scale is possible and thus supports the main claim of this thesis. Before this PhD project, no E-sail tether existed. The development of tether production and the results achieved brings the implementation of the most important E-sail component into the practical engineering realm and thus significantly advances the E-sail development. The produced 1 km tether was the most important objective of the ESAIL EU FP7 -framework project. Aurinkotuulipurje voi tulevaisuudessa korvata raketit ja ionimoottorit planeettojen välisissä kuljetuksissa. Suunniteltu täysikokoinen aurinkotuulipurje käyttää 100 kertaa 20 km pitkiä metallisia liekoja, jotka avataan keskipakoisvoiman avulla 40 km leveäksi purjeeksi. Liekojen tulee olla sähköä johtavia ja pinta-alaltaan mahdollisimman pieniä. Mikrometeoroidit, avaruuden tomuhiukkaset aiheuttavat merkittävän ongelman. Ne katkaisevat yksittäisen 20 km pitkän 50 µm halkaisijaltaan olevan metallilangan keskimäärin 160 kertaa vuodessa. Ratkaisu ongelmaan on monisäikeinen lieka, jossa yksittäisen langan katkeaminen ei merkittävästi lisää koko liean katkeamistodennäköisyyttä. Tutkimukseni pääväite…