Laser Propulsion Research Articles

Afocal combinations and focus control for laser launch telescopes

In the field of ground-based telescopes, laser guide stars (LGS) are artificial stars formed in the sky to serve as a reference for the adaptive optics. The artificial star should have a small lateral extent as this is an important factor for how well the adaptive optics can compensate for atmospheric turbulence. The laser launch telescope (LLT) is a key component of the LGS facility. It uses an afocal system to increase the waist of the laser, therefore reducing the beam divergence and limiting the size of the star. We describe the design process of LLTs and show how a combination of two afocals with controlled defocus can be used to optimize the LGS. First, the impact of defocusing a single afocal and tuning the position of the input beam waist is presented. We then demonstrate how an intermediary afocal system can be used to vary the properties of the beam at the input of the second afocal. With such a configuration, a controlled defocus of both afocals can be performed to tune the artificial star size. Moreover, the two afocals configuration can be used to adapt the system to the amount of atmospheric perturbations affecting the beam during the upward propagation.

Feasibility study of a laser launch system for picosatellites and nanosatellites in low-earth orbits

Laser propulsion is a space transportation system that obtains thrust from a laser beam that is transmitted from the ground as an energy source. In this study, we evaluated the launch performances of two types of laser propulsion systems in a circular orbit at an altitude of 500 km. One propulsion used the heating system of the laser-sustained plasma (LSP) type, and the other propulsion had the heating system of the porous-carbon heat exchange (hereinafter PHX) type. Assuming a laser power of 500 kW, which is the maximum laser power that is commercially available, the payload masses were estimated to be 0.679 and 0.640 kg for the LSP and PHX systems, respectively. This result shows that the laser power level that is currently available enables the launch of a picosatellite. The laser power values required to launch a nanosatellite less than 10 kg were estimated to be 6.8 and 6.4 MW for the LSP and PHX systems, respectively. Finally, the launch cost was estimated as a function of the number of launches. Our results show that, when the picosatellite was launched 1000 times, the launch cost became comparable with that of a conventional nanosatellite launch. Subsequently, the launch cost decreased to one-twentieth the cost of a conventional chemical rocket.

Performance and Characterization of a Neutral Beam Propulsion Technology Demonstrator

A neutral beam propulsion technology demonstrator has been fabricated and tested. It uses gas diffusion neutralization to create a globally neutral plasma from an ion source. Thrust measurements for the neutral beam demonstrate that thrust at the very low levels produced by this system can be measured during thermal drift of the variable amplitude hanging pendulum with extended range thrust stand. The beam energy, which exhibits good quantitative agreement with the thrust measurements, is measured as a function of neutralizer gas flow rate using a graphite calorimeter. A Faraday cup is used to measure the neutralization of the beam. These measurements generally exhibit quantitative agreement with predictive analytical and numerical models. Losses owing to the use of a grounded metal neutralizer are discussed, and it is quantitatively demonstrated through thrust, neutralization, and calorimetry measurements that the neutralizer is the source of the performance losses.

Reaching for the stars: The case for cooperative governance of directed energy technologies

ABSTRACTThe kind of advances in spaceflight envisioned in the mid-twentieth century have largely failed to materialize, thereby limiting space exploration to relatively small areas of a very large galaxy. That will change with the advent of directed energy technologies, specifically laser propulsion. The privately funded Breakthrough Starshot program is already working on such a propulsion system to carry nanosatellite Star Chips to the nearest star system, Alpha Centauri. But powerful lasers – a dual-use technology much like rocketry, nuclear energy, and cyber technology, which have both security-related and civilian uses – have been largely stigmatized as weapons. While security concerns about the use of large lasers are certainly justified, the development of Starshot and other big, multinational science programs can have positive national and international outcomes. Therefore, the use of a large laser array as a propulsion system will require, much like other large multinational cutting-edge science programs, a negotiated, cooperative governance system. Those negotiations should begin soon.

Flow and Impulse of Annular Laser-Pulse-Induced Explosions on a Sphere

A donut-sphere laser launch system has been suggested for launching a sphere capsule stably along an annular cross-sectional “donut” laser beam. In this study, the thrust and side force are numerically investigated using a simple explosion source model considering the beam size, explosion source energy, and axial offset between the beam and target as the parameters. It is established that the thrust, as well as the side force, is sensitive to the ratio of the laser-beam radius to the sphere radius . The impulsive thrust force is maximum at approximately, whereas a positive side force (i.e., recovery force) can be generated only if is greater than a critical value of approximately 0.8. These trends are explained with respect to shock focusing and laser ablation.

Thrust enhancement and propellant conservation for laser propulsion using ultra-short double pulses

Investigations on the thrust generated during ablation of copper with single, double, or triple ultra-short laser pulses are presented in this paper with the goal to find the optimum parameters for laser propulsion thrusters. On the basis of high-precision weighing experiments, it is shown that the material initially ablated by the first pulse and redeposited by the second pulse of a double pulse leads to a significant increase of thrust. Hence, double pulses are a suitable method to propel vessels in space with enhanced thrust values while at the same time saving propellant material.

Ultrafast photomechanical transduction through thermophoretic implosion

Since the historical experiments of Crookes, the direct manipulation of matter by light has been both a challenge and a source of scientific debate. Here we show that laser illumination allows to displace a vial of nanoparticle solution over centimetre-scale distances. Cantilever-based force measurements show that the movement is due to millisecond-long force spikes, which are synchronised with a sound emission. We observe that the nanoparticles undergo negative thermophoresis, and ultrafast imaging reveals that the force spikes are followed by the explosive growth of a bubble in the solution. We propose a mechanism accounting for the propulsion based on a thermophoretic instability of the nanoparticle cloud, analogous to the Jeans’s instability that occurs in gravitational systems. Our experiments demonstrate a new type of laser propulsion and a remarkably violent actuation of soft matter, reminiscent of the strategy used by certain plants to propel their spores.

Development of High Brightness Solid-State Laser Technology

Laser propulsion, laser energy transfer, and other major research directions have proposed a major demand for high brightness solid-state laser technology, making relevant research remain the focus of international attention. This paper presents the macro demand for high brightness solid-state laser technology and summarizes the current situation of technology research in China and abroad, its development trend, and the problems for further development. Based on this, the key technologies of high brightness solid-state lasers are analyzed, and some suggestions are proposed for future development. The slab laser and fiber laser have become the focus of research owing to their outstanding advantages. While the output power of a single laser is constantly improving, the laser output with high brightness can be realized using the beam combination method. Key technologies should be promoted to form a technical system as soon as possible, such as new laser materials, high-ranking semiconductor laser pump source, high precision packaging process, adaptive beam control, and key components for beam combination. It is proposed to establish research projects for the solid state laser technology that is represented by the surface gain slab laser technology and has a good potential for development. The research and accumulation of common basic technologies should be strengthened to lay a solid foundation for the continuous improvement of output brightness, conversion efficiency, and power mass radio of solid-state laser in the future.

Beam Riding Performance of Laser Propulsion Vehicle with Multi-Parabola Configuration

Beam Riding Performance of Laser Propulsion Vehicle with Multi-Parabola Configuration

Solar One: A Proposal for The First Crewed Interstellar Spacecraft

In this paper it is presented the concept and design of a new type of spacecraft that could be used to make the first manned interstellar travel. Solar one would integrate three near-term technologies, namely: compact nuclear fusion reactors, extremely large light sails, and high-energy laser arrays. A system of lenses or mirrors to propel the sail with sunlight is suggested as an alternative to laser propulsion. With a mile-long light sail, Solar One could reach an average of 22% the speed of light, arriving to the closest potentially habitable exoplanet in less than 19 years with the help of a Bussard scoop producing reverse electromagnetic propulsion. Key challenges are reducing the weight of continuous-wave lasers and compact fusion reactors as well as achieving cryo-sleep and artificial gravity.

Theoretical Examination of Laser Propulsion for Aerospace Application

This paper represents the significance of laser Propulsion for Aerospace Application. Laser impetus is a type of shaft controlled drive where the vitality source is a remote laser framework and separate from the response mass. This type of drive varies from a regular concoction rocket where both vitality and response mass originate from the strong or fluid charges continued board the vehicle. The ongoing tests on laser Propulsion demonstrate that, a little quad copter has flown for 12 hours and 26 minutes charged by a 2.25 kW laser (controlled at not exactly 50% of its ordinary working current), utilizing 170 watt photovoltaic exhibits as the power recipient, and a laser has been shown to charge the batteries of an unmanned elevated vehicle in trip for 48 hours. For shuttle, laser electric impetus is considered as a contender to sunlight based electric or atomic electric drive for low-push impetus in space. In the present examination, correlation of execution parameters of Laser Propulsion with Solar Propulsion are assessed hypothetically.

8 phase-shift-keying optical millimeter-wave signal generation by electro-optical phase modulator-based photonic frequency quintupling

We have proposed an 8 phase-shift-keying (PSK) optical millimeter-wave (MMW) signal generation scheme with frequency quintupling enabled by an electro-optical phase modulator (PM) and a wavelength selective switch. In this scheme, the radio frequency (RF) carrier with 8PSK signal is modulated on the lightwave via the PM with simple precoding but constant Euclidean distance, and is recovered to the original 8PSK signal with the frequency-quintupling RF carrier based on the phase periodicity of an 8PSK signal. By optimizing the voltage amplitude of the 8PSK RF driving signal, the generated frequency-quintupled 8PSK MMW signal is maximized at a given laser launch power. A radio over fiber simulation link is built to demonstrate the theoretical analysis. The simulated constellations and bit-error-rate curves show that the frequency-quintupling 8PSK MMW signal has good transmission performance. The simulation results agree well with our theoretical prediction.

Impulse Generation and Stabilization Performance of a Doughnut–Spherical Laser Launch System

A conceptual laser launch system of a spherical vehicle propelled by a doughnut-shaped laser beam is expected to accelerate the spherical vehicle continuously to the orbit velocity along a laser beam. Once lateral offset between the axis of the laser beam and the center of the sphere is generated, lateral force is generated to recede the offset. In this study, a pulsed Neodymium-doped Yttrium Aluminum Garnet laser beam of a doughnut-shaped cross section is focused on a 10-mm-diameter aluminum sphere. The impulse components, parallel and lateral to the laser beam, are first investigated experimentally using a pendulum method. As a result, the ratio of the doughnut beam radius to the target radius is found to have a major impact on the impulse. For a relatively small value of at 0.56, at atmospheric pressure, the impulse is enhanced due to the focusing of the toroidal blast wave, whereas the shock focusing effect is negligible for a larger value of at 0.86. On the other hand, must be larger than 0.83 to generate the restoring lateral force.

Design of a Gas Diffusion Neutralizer in Support of Neutral Beam Propulsion

Neutral beam propulsion draws upon the technology used in heating tokamaks to develop globally neutral electric propulsion. This propulsion technology is advantageous when deflecting or otherwise interacting with asteroids, as traditional, quasi-neutral electric propulsion may produce undesirable charging of the asteroid’s surface. Gas diffusion neutralization is presented as the method for converting energetic argon ions to fast neutrals. The required gas density to achieve the highest neutralization for a given ion energy is presented. Sizing relations and thruster performance for a neutral beam are also presented. It is shown that neutral beams for space propulsion are feasible in terms of the required power and specific impulse. COMSOL simulations of the neutralization chamber were conducted in order to identify geometries that would reduce the flow rate required for neutralization.

Possible utilization of space debris for laser propulsion

Laser propulsion perspectives become more realistic with the development of laser systems as well as the necessity to resolve space junk problem and to perform high specific impulse interplanetary flights. Unlike others, laser thrusters can use virtually any type of fuel by turning it into plasma; this provides great abilities for harvesting working medium in space instead of bringing it from the Earth. This and ability to reuse external laser source intensively could save a lot of money and broaden abilities for thrusterless small satellites (nano- and pico- especially) and constellations of those. For the first time, we considered several options to use space debris objects (including out-of-use satellites, rocket stages) as a fuel for spacecraft with laser thruster. We evaluated possible mass consumption, thrust, velocity and energy efficiency performance, as well as optimal laser impact regimes, demanded velocity increment and time scale for different missions. We have shown that sufficient momentum to make 1 ton low Earth orbit object burn in the atmosphere can be produced by ablation of 10 kg only. Our findings appear to be rather realistic in terms of state-of-art launchable lasers, surface scanning systems and cost effect.

Interferometric method for specific impulse determination

One of the main figures of merit in laser-ablative propulsion is the specific impulse, Isp, defined as the impulse per unit weight of fuel, and it is related to the exhaust velocity, ve, by the acceleration of gravity, Isp = ve / g. Being a key magnitude, Isp needs to be accurately determined. It is usually inferred from other measurable quantities: the impulse coupling coefficient, Cm, defined as the ratio of the target momentum produced to the incident laser pulse energy, and Q * , the laser energy consumed per unit weight of ablated target material. Thus, Isp is calculated as Isp = CmQ * / g. However, single pulse ablated mass leading to Q * is in the nanogram scale and cannot be directly measured by weighting the targets. So, mass loss measurements are performed by analyzing the volumes of the craters produced by a large number of laser pulses. These procedures lead to larger than desired uncertainties in the Isp values. On the other hand, more precise measurements of Isp can be carried out from the direct measurement of the exhaust velocity of the ejected particles by interferometric methods. In this work, a system based on a Nomarsky interferometer has been set up for the time-resolved diagnostic in the nanometric scale of laser ablation plumes. The performance of the implemented system was first validated by measuring the Isp produced by aluminum targets and solid propellants based on metal/salt mixtures. The Cm dependence on laser parameters and binary composition of these propellants have been determined in previous works with a torsion pendulum and a piezoelectric sensor. Once the interferometer performance is characterized, the Isp produced by solid propellants composed of metal (Zn) and metal oxides (ZnO) matrices doped with nanoparticles of different materials is determined and compared.

Imperative of adopting a new access-to-space paradigm and the role of the laser ablation propulsion launch system (LAPLaS)

In the not so distant future, the laser ablation propulsion rockets powered by ground-based high average power laser will challenge the existing techniques of accessing space based on chemical propulsion. Chemical rocket propulsion, which made access to space possible to begin with and continues to be the only technology in use to that end, cannot, however, adequately serve the emerged and quickly growing launch-to-orbit needs of the pico-nano-micro-satellites niche markets. No further technological improvements in chemical rocket propulsion can change its well-known inherent limitations and disadvantages. The ongoing and imminent developments in the satellites’ markets as well as the timeless fundamental need in robust low-cost ground-to-orbit logistics urgently call for adopting a new game-changing technological paradigm for accessing space. By elaborating and expanding on the potentially key role of the laser ablation propulsion launch system in enabling the affordable and safe access to space, this paper logically continues the author’s previous work “Optimizing access to space: ground-to-orbit logistics framework (GOLF)” published in 2017 in the New Space journal.

Launching swarms of microsatellites using a 100 kW average power pulsed laser

Transferring small payloads from Earth to low Earth orbit (LEO) and to interplanetary space using laser ablation propulsion is a new application of pulsed laser ablation propulsion, which offers parameters not available with chemical propulsion. In earlier work, we showed how to use a 1 MW average power pulsed laser to launch a 25 kg satellite from LEO to a Mars Hohmann transfer orbit in 18 minutes. Here, we discuss a lower-power application that can achieve the same result, and also cheaply and rapidly launch swarms of microsatellites into geosynchronous orbit (GEO) for communication, Earth observation, and observation of assets in GEO. The result will be a network of satellites with different functions that is robust to failures. Laser propulsion offers orbit/launch mass ratio m/M impossible with chemical rockets as well as low launch cost/kg. The main purpose in this paper is to illustrate satellite launch with repetitive pulse lasers at realistic laser average power levels. The benchmark laser has 80 ps pulsewidth, 5 kJ pulse energy, 355 nm wavelength (third Nd harmonic), and 20 Hz pulse repetition rate, using the “L’ADROIT” laser station design. To minimize laser power, we employ eight loops of steadily increasing apogee, propelled at perigee by a L’ADROIT laser in LEO, followed by a circularization “burn” at apogee using a second L’ADROIT in GEO with similar laser power. We estimate the final mf/M ratio for these maneuvers to be 43%–53%, delivering 10.8 kg into a Mars Hofmann transfer orbit and 13.2 kg to GEO. The ablated mass is contained in a spherical shell surrounding the satellite payload composed of a mixture of metal powder and polyoxymethylene. The mixture is tailored to the mission to give a matched specific impulse Isp and momentum coupling coefficient Cm. For the GEO insertion, the ablation shell splits and is re-entered after one orbit by a final “burn” from the GEO laser.

Nanophotonic Heterostructures for Efficient Propulsion and Radiative Cooling of Relativistic Light Sails.

Light sails propelled by radiation pressure from high-power lasers have the potential to achieve relativistic spaceflight. In order to propel a spacecraft to relativistic speeds, an ultrathin, gram-sized light sail will need to be stably accelerated by lasers with ∼MW/cm2 intensities operating in the near-infrared spectral range. Such a laser-driven sail requires multiband electromagnetic functionality: it must simultaneously exhibit very low absorptivity in the (Doppler-broadened) laser beam spectrum in the near-infrared and high emissivity in the mid-infrared for efficient radiative cooling. These engineering challenges present an opportunity for nanophotonic design. Here, we show that designed thin-film heterostructures could become multifunctional building-block elements of the light sail, due to their ability to achieve substantial reflectivity while maintaining low absorption in the near-infrared, significant emissivity in the mid-infrared, and a very low mass. For a light sail carrying a payload, we propose a relevant figure of merit-the reflectivity adjusted area density-that can capture the trade-off between sail mass and reflectivity, independent of other quantities such as the incident beam power, phased array size, or the payload mass. Furthermore, we present designs for effective thermal management via radiative cooling and compare propulsion efficiencies for several candidate materials, using a general approach that could apply to a broad range of high-power laser propulsion problems.

The feasibility of deflecting asteroid 2017 PDC using neutral beam propulsion

The neutral beam for asteroid control (NBAC) technology is a globally neutral plasma thruster that seeks to fill the operational gap between high impulse and slow push asteroid deflection methods. Additionally, NBAC can be used to modify both the spin state and trajectory of an asteroid. In this work, we study NBAC's ability to de-spin and/or deflect an asteroid, considering a range of asteroid sizes, asteroid spectral types and assuming the asteroid's orbit is that of the hypothetical asteroid 2017 PDC. The analysis assumes that four NBAC-equipped spacecraft are deployed, each with a 10 keV neutral beam emitter. The achieved deflection and the applicability of NBAC to a deflection campaign is presented. This work quantifies the impact of uncertainty in asteroid composition on propellant and deflection time requirements for NBAC. Assuming one perihelion passage prior to Earth-impact, NBAC can successfully deflect a 100–150 m S, C, B, or Xc-type asteroid on the 2017 PDC trajectory. Loss of a spacecraft during deflection and its effect on mission success is also investigated. Failure of one or two (of the four) NBAC-carrying spacecraft during deflection does not preclude successful deflection for a set of sizes and densities. Propellant usage and time required to fully de-spin representative asteroids are also presented. Additionally, the time required for total de-spin is compared to the time required for partial arrest. Partial arrest of unstable spinners is possible under mission constraints for a range of asteroid sizes and densities. Total arrest can be achieved for less than 60 kg per spacecraft for a four-spacecraft NBAC system.