Laser Ablation Could Boost Jet, Rocket Fuel Efficiency

A new approach to the concept of laser propulsion could launch satellites into orbit and push aircraft past Mach 10 with enhanced fuel efficiency.

By ablating solid fuel inside a jet nozzle, laser pulses could increase the speed of gas flow out of the system to supersonic speeds. The approach was proposed by Yuri Rezunkov of the Institute of Optoelectronic Instrument Engineering and Alexander Schmidt of the Ioffe Physical Technical Institute in St. Petersburg.

Mach number distribution simulation for a supersonic nozzle with an off-axis paraboloid; (a) describes the system without an ablative jet, (b) describes the system with one. Courtesy of Yuri Rezunkov/Institute of Optoelectronic Instrument Engineering.

Currently, the maximum speed of a rocket or plane is limited by the amount of solid or liquid fuel that it can carry. Achieving higher speeds means that more fuel must be burned. But adding more fuel would also add more weight, requiring ever greater thrust to move the craft.

If the craft could be pushed, on the other hand, it wouldn’t need to carry so much fuel to reach high speeds. One proposed way to give this push is through laser ablation, where a pulse ionizes material on or within the craft, creating a plasma plume that generates thrust.

This approach would be limited, Rezunkov and Schmidt said, by the instability of supersonic gases as they flow through a gas nozzle, as well as the production of shock waves that would “choke” the nozzle and reduce thrust.

The pair modeled optimum gas-plasma pressure and temperature in the ablation region, as well as mass consumption rate of the ablated solid propellant. Their technique would cause the plasma plume to flow close to the interior walls of the nozzle to avoid choking it.

The work was published in Applied Optics (doi: 10.1364/AO.53.000I55).