Recently we became interested in applying previous work with liquid fueled laser powered minithrusters for
spacecraft orientation to the conceptual design of a multi-newton thruster based on the same principles. Solid-fuel
configurations (such as the fuel tapes used in the Photonic Associates microthruster) are not amenable to the
range of mass delivery rates (g/s to g/s) necessary for such an engine.
We will discuss problems for this design which have been solved, including identifying a practical method of
delivering liquid fuel to the laser focus, avoiding splashing of liquid fuels under pulsed laser illumination, and
avoiding optics clouding due to ablation backstreaming on optical surfaces from the laser-fuel interaction region.
We have already shown that Isp = 680 seconds can be achieved by a viscous liquid fuel based on glycidyl azide
polymer and an IR-dye laser absorber.
The final problem is mass: we will discuss a notional engine design which fits within a 10-kg "dry mass"
budget. This engine, 80kg mass with fuel, is designed to fit within a 180-kg spacecraft, and use 3kW of prime
power to deliver a Δv of 17.5 km/s to the spacecraft in sixteen months. Its specific impulse will be adjustable
over the range 200sp<3,600 seconds and maximum thrust will be 6N, based on performance which has been
demonstrated in the laboratory. Such an engine can put small satellites through demanding maneuvers in short
times, while generating the optimum specific impulse for each mission segment. We see no reason why
Isp = 10,000 seconds cannot be achieved with liquid fuels.