Demonstration of a mN-Class Photonic Laser Thruster

Abstract

Demonstration of a mN-Class Photonic Laser Thruster
Young K. Bae,* Ph.D., Y.K. Bae Corporation, USA
Hagop Injeyan, Ph.D., A&I Consulting, USA
Jörg Neuhaus, Ph.D., Dausinger + Giesen GmbH, Germany

The Photonic Laser Thruster (PLT) aims to overcome “the tyranny of the rocket equation,” which implies that the required onboard fuel mass exponentially increases as a function of the destination velocity in conventional rocketry. When scaled, PLT is projected to make space endeavours beyond earth-orbits commercially viable. To improve the efficiency and reduce the required Size, Weight and Power (SWaP) of the spacecraft, PLT amplifies thrust by recycling photons in a high-finesse active optical resonance cavity formed between two spacecraft platforms. Because PLT does not use any propellant and can control thrust amount and direction orders of magnitude more precisely than conventional thrusters, PLT permits near-term applications that are stepping stones towards longer-term applications, such as manned interplanetary commutes. The near-term applications include earth-orbit spacecraft maneuvering and precision formation flying of small spacecraft, which would open doors to an entirely new generation of planetary, heliospheric, and Earth-centric missions.
Under the auspice of the NASA Innovative Advanced Concepts (NIAC) program, we have successfully scaled PLT thrust by a factor of 100 to 3.5 mN and increased the power-to-thrust conversion efficiency by a factor of 10. Our success resulted from an adaptation of state-of-the-art, highly efficient Thin Disk Laser (TDL) technology, which significantly decreased the total laser cavity loss of the recycled photons by reducing absorption and scattering in the laser gain medium and improved thermal management. The PLT has generated a maximum intracavity laser power over 500 kW at a modest extractable power level of 550 W, and thus is 900 times more power efficient than a conventional laser sail. The intracavity power was estimated by measuring the laser power transmitted through an outcoupler mirror. Simultaneously, the photon thrust was measured directly on a newly-developed NIST/Scientech radiation pressure sensor. The results of these two measurements agree within 10%. The difference is attributed primarily to the errors from the mirror transmittance measurement and the outcoupler heating. Moreover, the PLT was demonstrated to maneuver a 1U CubeSat via photon thrust beaming on a 2-m-long air track without degrading the optical resonance condition. The low friction air track simulated a zero-gravity environment.
This presentation will briefly review the history of PLT and focus on the updated developmental status. This will be followed by specific examples of near-term applications, such as virtual space telescopes and propellant-free station keeping of spacecraft. The conclusion will consist of projections of PLT scaling, efficiency enhancement and potential future applications.