Space debris mitigation in Low Earth Orbit (LEO) using high power pulsed lasers

Mitigating space debris with lasers is investigated as a possible mechanism for contactless space debris deflection in Low Earth Orbit (LEO). This deflection mechanism can be carried out by irradiating the space debris surface with a high-power laser beam. The energy absorbed by the surface of the debris, from the laser beam, sublimates the irradiated surface, transforming it to gas from solid. The ablated material is formed into a plume of ejecta, which acts against the orbital debris if the laser is beamed in the right direction; it produces a small push or thrust that deflects the debris by reducing its orbital velocity, altitude and eventually its lifetime in orbit. This approach could also be used to push space debris away from operational satellites paths. Laser ablation depends mainly on understanding the physical properties of both, the laser beam and the space debris. The interaction process for three different commonly used spacecraft materials are illuminated by a laser beam and investigated both experimentally and by using theoretical models. Experimental results and theoretical verifications are employed to evaluate the feasibility of the ablation model and to understand its performance in producing an effective deflection of space debris. This was investigated using Nd3+ Glass laser pulses with three metals: nickel (Ni), aluminium (Al) and copper (Cu). The Nd3+ Glass laser operated at a wavelength of 1.06 μm that provided intensities just below the threshold for plasma formation. This interaction produces surface power intensities ranging between one GW/m2 to one TW/m2, which produces high order temperature gradients that cause non-equilibrium energy transport phenomenon. This phenomenon cannot be explained by classical theories. The results have been used for the enhancement of the ablation model. Additional enhancements included the temperature penetration in the target surface. The surface temperature transients of metals due to laser interaction have also been investigated, and heat transfer is simulated by utilising a kinetic particle model, which captures the dominant energy transport processes. This model of energy transport permits determination of the significant decline in temperature gradients and the non-equilibrium conditions that occur between the Fermi surface conduction electrons and lattice phonons. This results in an accurate temperature distribution calculation within the space debris. The laser pulse specification and the properties of the space debris material were specified for simulation. The kinetic model has been used to simulate the spatial temperature distribution growth in the space debris when illuminated with a 1.06 μm wavelength Nd3+ Glass laser. The evaporation physics are also incorporated into the kinetic model. The average mass flow rate has been evaluated. A critical difference has been discovered between the experimental results and the predicted results using the classical Fourier Theory. The experimental data of the target surface temperatures are compared with Fourier and electron Kinetic theories. The experimental results validate the theoretical results and model improvements. It also illustrated the inaccuracy of Fourier theory regarding its solution of steep energy gradients and its failure to illustrate the non-equilibrium energy transport state, which grows between electrons and lattice phonons. It was noticed that the electron Kinetic theory results provide sufficient agreement with the experimental results below the boiling point and give a much better model than Fourier theory above the boiling temperature. The enhancements have permitted the laser specifications and the performance of the ablation treatment to be characterised. The performance of orbital debris mitigation with pulsed lasers outperformed alternative techniques that can produce a small contactless push on space junk. This method avoids sending complicated spacecraft into orbits to take space debris away from Earth orbits. The laser power that is required to reduce the altitude and the orbital velocity of space debris were predicted and calculated theoretically. The performance has been assessed by its capability to move small debris, centimetre size, by at least a couple of m/s. The results confirmed the possible benefits of using lasers to mitigate space debris in LEO. Employing current technologies together with a high Technology Readiness Level (TRL), an affordable and compact laser system could be successfully constructed and attached to traditional artificial satellites as a space-based laser system. Such a system could demonstrate the method, synergies and techniques of laser ablation. Mission complexity and the extra mass are saved by the direct debris ablation process, which can operate at a relatively small distance compared to a ground-based laser system. The analysis thus confirms the feasibility of utilising space-based laser systems and the applicability of the model’s experimental validation