Laser ablation of organic coatings as a basis for micropropulsion

Abstract The micro laser plasma thruster (μLPT) is a new micropropulsion device which is competitive with the pulsed plasma thruster (μPPT) for steering or propelling 10–100 kg ‘microsatellites’. It is driven by a cluster of fiber-coupled infrared diode lasers, focused onto a two-layer ablating tape. Electrical to optical conversion efficiency is 50%. The tape consists of a transparent supporting layer through which the light passes without perforating it, and an absorbing fuel layer, which is heated by the laser to form a jet on the side of the tape opposite to the laser. The μLPT operates on spacecraft bus voltage, and weighs 0.85 kg. At the millisecond pulse durations required to enable the diodes to achieve ablation threshold in a 25-μm focal spot, target materials are limited to those of low thermal conductivity, e.g. polymers. Passive ablatants produced 7.5 dyn thrust and a coupling coefficient ( C m ) of 8 dyn/W. Specially-designed, carbon-doped exothermic photopolymers produced up to 68 dyn thrust with 2.1 W average optical power, achieving an exhaust velocity of 2–3 km/s in continuous tests and up to 12 km/s in single-shot static tests. We discuss the design and performance of these photopolymers, recent diagnostics of μLPT plasma plume and latest performance results.