Background

Beam-powered propulsion, also known as directed energy propulsion, is a class of aircraft or spacecraft propulsion that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a microwave or a laser beam and it is either pulsed or continuous. A continuous beam lends itself to thermal rockets, photonic thrusters and light sails, whereas a pulsed beam lends itself to ablative thrusters and pulse detonation engines.

The rule of thumb that is usually quoted is that it takes a megawatt of power beamed to a vehicle per kg of payload while it is being accelerated to permit it to reach low earth orbit.

This technology is also part of the research aim of the “To The Stars Academy of Arts & Sciences“. I compiled the below documents to explore the research the U.S. Government and Military has already collected and what they have tested in regards to the technology.

Document Archive

(In chronological order from most recent to oldest)

Perspective on One Decade of Laser Propulsion Research at Air Force Research Laboratory, November 2017 [13 Pages, 1MB] – The Air Force Laser Propulsion Program spanned nearly 10-years and included about 35-weeks of experimental research with the Pulsed Laser Vulnerability Test System of the High Energy Laser Systems Test Facility at White Sands Missile Range, New Mexico, WSMR/HELSTF/PLVTS. PLVTS is a pulsed CO2 laser that produces up to 10 kW of power in ~ 10 cm2 spot at wavelength of 10.6 microns. The laser is capable of a pulse repetition rate up to 25 Hz, with pulse durations of about 20 microseconds. During the program basic research was conducted on the production of propulsion thrust from laser energy through heating of air and ablation of various candidate rocket propellant fuels. Flight tests with an ablation fuel (Delrin) and air were accomplished with a model Laser Lightcraft vehicle that was optimized for propulsion by the PLVTS at its maximum power output, 10kW at 25 Hz, 400 J/pulse. Altitudes exceeding 200-feet were achieved with ablation fuels. The most recent contributions to the technology included development of a mini-thruster standard for testing of chemically enhanced fuels and theoretical calculations on the performance of formulations containing ammonium nitrate and Delrin. Results of these calculations will also be reported here.

Earth to Orbit Beamed Energy Experiment, September 2017 [5 Pages, 0.81MB] – As a means of primary propulsion, beamed energy propulsion offers the benefit of offloading much of the propulsion system mass from the vehicle, increasing its potential performance and freeing it from the constraints of the rocket equation. For interstellar missions, beamed energy propulsion is arguably the most viable in the near- to mid-term. A near-term demonstration showing the feasibility of beamed energy propulsion is necessary and, fortunately, feasible using existing technologies. Key enabling technologies are large area, low mass spacecraft and efficient and safe high power laser systems capable of long distance propagation. NASA is currently developing the spacecraft technology through the Near Earth Asteroid Scout solar sail mission and has signed agreements with the Planetary Society to study the feasibility of precursor laser propulsion experiments using their LightSail-2 solar sail spacecraft. The capabilities of Space Situational Awareness assets and the advanced analytical tools available for fine resolution orbit determination now make it possible to investigate the practicalities of an Earth-to-orbit Beamed Energy eXperiment (EBEX) – a demonstration at delivered power levels that only illuminate a spacecraft without causing damage to it. The degree to which this can be expected to produce a measurable change in the orbit of a low ballistic coefficient spacecraft is investigated. Key system characteristics and estimated performance are derived for a near term mission opportunity involving the LightSail-2 spacecraft and laser power levels modest in comparison to those proposed previously. While the technology demonstrated by such an experiment is not sufficient to enable an interstellar precursor mission, if approved, then it would be the next step toward that goal.

Review Of Laser Lightcraft Propulsion System, October 16, 2017, by Dr. Eric W. Davis [13 Pages, 1MB] – Laser-powered “Lightcraft” systems that deliver nano-satellites to LEO have been studied for the Air Force Research Laboratory (AFRL). The study was built on the extensive Lightcraft laser propulsion technology already developed by theoretical and experimental work by the AFRL’s Propulsion Directorate at Edwards AFB, CA. Here we review the history and engineering-physics of the laser Lightcraft system and its propulsive performance. We will also review the effectiveness and cost of a Lightcraft vehicle powered by a high-energy laser beam. One result of this study is the significant influence of laser wavelength on the power lost during laser beam propagation through Earth’s atmosphere and in space. It was discovered that energy and power losses in the laser beam are extremely sensitive to wavelength for Earth-to-Orbit missions, and this significantly affects the amount of mass that can be placed into orbit for a given maximum amount of radiated power from a ground-based laser.

MOVEMENT AND MANEUVER IN DEEP SPACE: A Framework to Leverage Advanced Propulsion, April 2017 [72 Pages, 7.5MB] – This analytical study looks at the importance of Deep Space Operations and recommends an approach for senior policy leaders. Section 1 presents a capability requirements definition with candidate solutions and technology strategies. Section 2 recommends an acquisition and organizational approach. Section 3 provides an extended strategic rationale for deep space operations as a national priority.

Beamed-Energy Propulsion (BEP): Considerations for Beaming High Energy-Density Electromagnetic Waves Through the Atmosphere, May 2015 [58 Pages, 1.7MB] – A study to determine the feasibility of employing beamed electromagnetic energy for vehicle propulsion within and outside the Earth’s atmosphere was co-funded by NASA and the Defense Advanced Research Projects Agency that began in June 2010 and culminated in a Summary Presentation in April 2011. A detailed report entitled “Beamed-Energy Propulsion (BEP) Study” appeared in February 2012 as NASA/TM-2012-217014. Of the very many nuances of this subject that were addressed in this report, the effects of transferring the required high energy-density electromagnetic fields through the atmosphere were discussed. However, due to the limitations of the length of the report, only a summary of the results of the detailed analyses were able to be included. It is the intent of the present work to make available the complete analytical modeling work that was done for the BEP project with regard to electromagnetic wave propagation issues. In particular, the present technical memorandum contains two documents that were prepared in 2011. The first one, entitled “Effects of Beaming Energy Through the Atmosphere” contains an overview of the analysis of the nonlinear problem inherent with the transfer of large amounts of energy through the atmosphere that gives rise to thermally-induced changes in the refractive index; application is then made to specific beamed propulsion scenarios. A brief portion of this report appeared as Appendix G of the 2012 Technical Memorandum. The second report, entitled “An Analytical Assessment of the Thermal Blooming Effects on the Propagation of Optical and Millimeter- Wave Focused Beam Waves For Power Beaming Applications” was written in October 2010 (not previously published), provides a more detailed treatment of the propagation problem and its effect on the overall characteristics of the beam such as its deflection as well as its radius. Comparisons are then made for power beaming using the disparate electromagnetic wavelengths of 1.06 microns and 2.0 millimeters..

Numerical Analysis of a Single Microchannel Within a High-Temperature Hydrogen Heat Exchanger for Beamed Energy Propulsion Applications, February 2013 [8 Pages, 1.5MB] – The requirement that the propellants used in launch vehicle systems must also provide the thermal energy to be converted to kinetic energy in the rocket nozzle has plagued rocket designers since the dawn of the space age. Beamed propulsion systems, however, avoid this constraint by placing the energy source on the ground and transmitting the energy to the spacecraft via microwaves. This work computationally models three different heat exchanger channel designs for use in a beam propulsion spacecraft. It was found that despite the very small diameter of the microchannels, each design produced extreme temperature gradients across the channel cross section.

Investigation of Innovative Lightcraft Designs for Hypersonic Air Breathing and Rocket Flight by Beamed Energy Propulsion, June 2013 [251 Pages, 12.7MB] – The report has three parts: 1) Lightcraft inlet design: The work outlines the innovative streamtraced design methodology and a number of suitable lightcraft inlet designs. It also contains an analysis of laser detonation, a system level analysis of lightcraft flight and analysis of a ground test model. 2) Experimental ground testing. The lightcraft design documented in Part 1 was tested at the University of Southern Queensland’s hypersonic test facility. This report documents these tests that include both flow visualization and surface pressure measurements for a range of angles of attack. 3) Future flight test program. A feasibility study was performed to investigate how a future lightcraft test program may be conducted. A multi-part test program is described including trajectory and cost estimates.

Beamed-Energy Propulsion (BEP) Study, February 2012 [698 Pages, 96.8MB] – The scope of this study was to (1) review and analyze the state-of-art in beamed-energy propulsion (BEP) by identifying potential game-changing applications, (2) formulate a roadmap of technology development, and (3) identify key near-term technology demonstrations to rapidly advance elements of BEP technology to Technology Readiness Level (TRL) 6. The two major areas of interest were launching payloads and space propulsion. More generally, the study was requested and structured to address basic mission feasibility. The attraction of beamed-energy propulsion (BEP) is the potential for high specific impulse while removing the power-generation mass. The rapid advancements in high-energy beamed-power systems and optics over the past 20 years warranted a fresh look at the technology. For launching payloads, the study concluded that using BEP to propel vehicles into space is technically feasible if a commitment to develop new technologies and large investments can be made over long periods of time. From a commercial competitive standpoint, if an advantage of beamed energy for Earth-to-orbit (ETO) is to be found, it will rest with smaller, frequently launched payloads. For space propulsion, the study concluded that using beamed energy to propel vehicles from low Earth orbit to geosynchronous Earth orbit (LEO-GEO) and into deep space is definitely feasible and showed distinct advantages and greater potential over current propulsion technologies. However, this conclusion also assumes that upfront infrastructure investments and commitments to critical technologies will be made over long periods of time. The chief issue, similar to that for payloads, is high infrastructure costs.

New Technology and Lunar Power Option for Power Beaming Propulsion, October 2004 [14 Pages, 0.7MB] – Orbit raising missions (LEO to GEO or beyond) are the only missions with enough current traffic to even be seriously considered for power beaming propulsion. Even these missions cannot justify the development expenditures required to deploy the required new laser, optical and propulsion technologies or the programmatic risks. To be deployed, the laser and optics technologies must be spin-offs of other funded programs. The manned lunar base nighttime power requirements may justify a major power beaming program with 2MW lasers and large optical systems. New laser and optical technologies may now make this mission plausible. If deployed these systems could be diverted for power beaming propulsion applications. Propulsion options include a thermal system with an Isp near 1000 sec., a photovoltaic-ion propulsion systems with an Isp near 3000 sec., and a possible new optical coupled thermal system with an Isp over 2000 sec.

Two Temperature Modeling and Experimental Measurements of Laser Sustained Hydrogen Plasmas, May 1993 [244 Pages, 12MB] – Experiments have been performed which measured the global absorption and thermal efficiency of laser sustained hydrogen plasmas for the first time. Results include global absorption as high as 90% and thermal efficiency as high as 80%. These results validate laser propulsion as a feasible orbital transfer technology. A kinetic nonequilibrium model of laser sustained hydrogen plasmas has been formulated and solved. This model is the first of its kind and includes a discretized beam raytrace with a variable index of refraction based upon plasma electron number density. Model results have compared favorably with experimental results and the model has been used to provide predictions of LSP performance well outside the realm of experiments. Multiple model solutions have been obtained which are dependent upon initial conditions. No significant kinetic nonequilibrium was observed in LSP core regions for incident powers up to 700 kW. Beam refraction by the LSP has been observed to have a major effect on LSP performance. The methodology formulated in this document has direct applicability to two temperature modeling of arcjet plasmas, work which is currently underway at UIUC…. Beamed energy propulsion, Two temperature modeling, Laser sustained hydrogen plasmas.

Transport Processes in Beamed Energy Propulsion Systems, 1 Sep 1989-30 Sep 1991 [61 Pages, 2.6MB] – A model of a microwave-induced plasma propulsion system has been developed in one dimension for a transverse electric mode (TE sub 10) of operation in a rectangular waveguide. Available experimental data are compared to the computational results for the case of a planar propagating plasma wave and, using a TE sub 10 mode-shape approximation, for a wave propagating in a waveguide. Temperature profiles, plasma propagation velocities, velocity profiles, and absorbed power histories are obtained for flow of helium from .5 to 1 atmosphere pressure and 500 to 3000 watts input power at a frequency of 2. 45 GHz. The computational results show the observed jumping of the plasma towards the microwave source. Peak plasma temperatures range from 8000 to 9000 K over the input power range. For an input power of 1081.7 W the calculated percentage of power absorbed in approximately 70 percent for the planar case and 40 percent for the waveguide case. Comparisons with experimental data indicate other mechanisms (not involving transient processes), most likely associated with the nonequilibrium behavior of the plasma, are responsible for the disagreement between the model results and the observed plasma propagation velocities.

Energy Conversion Measurements in Laser-Sustained Argon Plasmas for Application to Rocket Propulsion, April 1988 [89 Pages, 4.6MB] – Laser Propulsion is the production of high specific impulse rocket thrust using a high power laser as a remote energy source. Specific impulses in excess of 1000 seconds are achievable because propellant temperatures are very high and low molecular weight gases can be used. This report focuses on the energy conversion mechanisms of laser-sustained plasmas in flowing argon. The status of AFOSR sponsored experiments to determine thermal efficiency and global absorption is detailed. An improved testing facility has allowed plasma operating conditions never before possible. The results indicate that nearly all of the input laser power can be absorbed by a plasma. Plasmas at elevated gas pressure have been tested, and preliminary results presented. Optimal operating conditions have yet to be determined for the available laser powers and gas pressures. Further experimentation at very high argon gas velocities ( 20 m/s) must be performed in order to completely characterize plasma behavior. Keywords: Beamed energy propulsion, Laser plasma formation.

Advanced Energy Conversion Concept for Beamed-Energy Propulsion, 21 August 1987 [202 Pages, 6.7MB] – The principal objective of this study was to perform basic research investigations into an innovative power conversion concept for trans atmospheric, beamed energy propulsion: a new class of External Surface Impulse (ESI) thrusters. This advanced thruster principle could be used for atmospheric VTOL, high acceleration, and lateral flight (e.g., short-term cruise ) propulsion of Single-Stage-To-Orbit (SSTO) beam-powered shuttlecraft of the next century. Three classes of ESI thrusters were initially examined: 1) simple thermal, 2) electrostatic and 3) electromagnetic. Beam power wavelengths from 10cm (microwave) to 0.3um (laser) were considered. The subsequent research effort concentrated on the simple thermal repetitively-pulsed ESI thrusters, energized with laser power and using air as the working fluid. Laser frequencies were selected because of the relative wealth of experimental data and theoretical research on laser impulse coupling which exists in the literature. The first year analytical effort has proven conclusively that such an engine can deliver high levels of thrust-to-beam-power at liftoff (e.g., at least an order-of-magnitude greater than beam-powered hydrogen-fueled rockets), with infinite specific impulse (decreased only, perhaps, by ablation of the thruster surface). Later along an orbital trajectory, the primary propulsion function would transition to other modes; upon leaving the atmosphere, the SSTO vehicle would continue in a pure rocket mode with a specific impulse (I sp) of 1000 seconds or more. Keywords: Advanced airbreathing propulsion, Beamed energy propulsion, External radiation heated (EH) thruster.

Experiments in Plasma Initiation and Laser Absorption in Flowing Gases, April 1985 [41 Pages, 1.9MB] – This report summarizes the preliminary results of experiments designed to characterize the thermal and gasdynamic behavior of laser-sustained plasmas in flowing argon. Calorimetric measurements of global absorption have been made over a range of laser power and pressure. Temperature field mappings yield preliminary estimates of thermal gas energy and radiative losses. An infrared imaging system has been used to study plasma properties as a function of power and flow rate. Spectroscopic and laser-induced fluorescence diagnostic systems, now being installed, are highlighted. Physical implications of the data are discussed, and results of a 2-D heat addition model are presented. Keywords include: Beamed energy propulsion, and Absorption of laser energy in gases.

A Plasma Initiation/Flow Chamber to Study CW Laser Beamed Energy Absorption in Light Gases, March 1984 [78 Pages, 3.6MB] – This report summarizes the research work that has been done in the past year, investigating the use of laser-sustained plasmas for propulsion applications. One focus of the research is the initiation of plasmas in inert gases using metal vapor seedants. Another is to define the operating characteristics of the dual-flow design by measuring temperatures, number densities, and global absorption. A pressure chamber has been built to permit observations of the plasma under wide ranges of pressure, flow conditions, and beam geometry. Laser energy absorption will be measured using a high -flux calorimeter, and temperature profiles will be found using a combination of spectroscopic relative line intensity measurements, thermocouples, infrared thermography, and possible laser induced fluorescence. The report summarizes the design and construction of the pressure chamber, optics, and related equipment, and discusses the techniques which will be used to analyze temperatures throughout the flowfield. Keywords include: Beam energy propulsion, CW laser application, Absorption of electromagnetic radiation.

Summary of Equipment Purchased and Description of Its Use: Support of Research in Beamed Energy Propulsion 1 Oct 84-1 Mar 86 [13 Pages, 0.9MB] – This report presents the description equipment purchased, the cost of that equipment, and how the equipment is being utilized to carry out research in the study of plasmas formed from high energy lasers. The program was funded by DoD as part of the University Research Instrumentation Program (URIP). Important results of the thermodynamic and heat transfer associated with laser sustained plasmas are presented. Keywords: Diagnostic equipment, Temperature measurement, Beamed laser energy, Propulsion.

Investigation of Beamed Energy Concepts for Propulsion. Laser/Propellant Coupling Analyses. Volume II, 2 Sep 75 – 1 Jul 76 [134 Pages, 22MB] – The objective of this program is to assess the feasibility of the beamed energy propulsion concept for Air Force missions. The work is divided into three major tasks: (1) system studies; (2) theoretical analyses of the coupling mechanisms between the beamed energy and propellant working fluid and (3) preparation of a test plan for the experimental investigation of the coupling processes for various laser/propellant combinations. The results of the study indicate that beamed energy propulsion is technically feasible. No fundamental obstacles have been identified. However considerable technical development is needed in many areas before the concept can be operationally implemented. Three promising applications have been identified. The laser powered tug can be cost effective compared to an advanced cryogenic tug. Apsidal rotation correction and drag make-up are two other missions where significant advantages may be realized for the laser powered concept. Extensive hardware development is required. Critical areas include the lasers, thrusters, thruster reaction chamber windows and the collection and coupling subsystems.

Investigation of Beamed Energy Concepts for Propulsion. Laser/Propellant Coupling Analyses. Volume I, 2 Sep 75 – 1 Jul 76 [262 Pages, 41.2MB] – The objective of this program is to assess the feasibility of the beamed energy propulsion concept for Air Force missions. The results of the study indicate that beamed energy propulsion is technically feasible. No fundamental obstacles have been identified. However considerable technical development is needed in many areas before the concept can be operationally implemented. In order to minimize the required collector area, laser concepts are preferred over microwaves. If space based laser transmitter concepts are to be cost effective they will require the availability of megawatt level space nuclear or solar power stations. In view of the large total energy required for each mission, ground based transmitters will be most cost effective when they are operated closed cycle from central station electric power. Laser transmitting ranges greater than several hundred nautical miles will result in excessive collector sizes. Therefore, ground based transmitters applications will be restricted to orbital functions which can be performed at low orbital altitudes. Three promising applications have been identified. The laser powered tug can be cost effective compared to an advanced cryogenic tug. Apsidal rotation correction and drag make-up are two other missions where significant advantages may be realized for the laser powered concept.

Additional Information