Israel I. Salvador

2‐D Airbreathing Lightcraft Engine Experiments in Quiescent Conditions

Ground‐breaking laser propulsion (LP) experiments were performed under quiescent conditions with a 25 cm wide, two‐dimensional Lightcraft model using a Lumonics TEA‐622 CO2 laser emitting ∼ 1 μs pulses. In preparation for subsequent hypersonic experiments, this static test campaign was conducted at ambient pressures of 0.06, 0.15, 0.30 and 1 bar with laser pulse energies of 150 to 230 J. Time‐variant pressure distributions, generated over engine “absorption chamber” walls, were integrated to obtain total impulse and momentum coupling coefficients (Cm) representative of a single propulsion cycle. Schlieren visualization of laser‐induced air breakdown and expanding blast waves was also accomplished. Surprisingly, the Cm results of 600‐3000 Ns/MJ were 2.5x to 5x greater than previous results from smaller Lightcraft models; this suggests that higher static Cm performance can likely be achieved in larger scale LP engines. This research collaboration, forged between the USAF and Brazilian Air Force, was carried...

Experimental Analysis of a 2‐D Lightcraft in Static and Hypersonic Conditions

Aiming at the hypersonic phase of the Earth‐to‐Orbit trajectory for a laser propelled vehicle, a 2‐D Lightcraft model was designed to be tested at the T3 Hypersonic Shock Tunnel at the Henry T. Nagamatsu Laboratory for Aerodynamics and Hypersonics. A high energy laser pulse was supplied by a Lumonics TEA 620 laser system operating in unstable resonator cavity mode. The experiments were performed at quiescent (no flow) conditions and at a nominal Mach number of 9.2. A Schlieren visualization apparatus was used in order to access both the cold hypersonic flowfield structure (without laser deposition) and the time dependent flowfield structure, taking place after the laser induced breakdown inside the absorption chamber. The model was fitted with piezoelectric pressure transducers and surface junction thermocouples in an attempt to measure pressure and heat transfer time dependent distributions at the internal surfaces of the model’s absorption chamber. The 2‐D model followed a modular design for flexibility...

Flow Visualization of Thrust‐Vectoring Lightcraft Engines with ∼1μs Pulsed TEA CO2 Laser

The thrust‐vectoring performance of four laser propulsion engine geometries were visualized using a twin Lumonics K922M pulsed TEA CO2 laser system, with a Cordin® high speed digital camera and Schlieren photography. Airbreathing mode engines were used to explore engine thrust‐vectoring behavior, as a function of: a) laser beam lateral offset from the engine axis of symmetry; b) laser pulse duration (∼50 ns spike with selectable 1.5 or 2.5 μs tail, depending upon laser gas mixture); and c) engine geometry (Lightcraft Type ♯150, ♯200, ♯250, and parabolic bell). The resulting Schlieren images visually prove thrust vectoring if the exhaust plume is responsible for the beam‐riding phenomenon. Parabolic bell engines demonstrate very little thrust vectoring ability, even at the large offsets nominal for beam‐riding and thrust‐vectoring in other geometries.

2‐D Air‐Breathing Lightcraft Engine Experiments in Hypersonic Conditions

Experiments were performed with a 2‐D, repetitively‐pulsed (RP) laser Lightcraft model in hypersonic flow conditions. The main objective was the feasibility analysis for impulse generation with repetitively‐pulsed air‐breathing laser Lightcraft engines at hypersonic speeds. The future application of interest for this basic research endeavor is the laser launch of pico‐, nano‐, and micro‐satellites (i.e., 0.1–100 kg payloads) into Low‐Earth‐Orbit, at low‐cost and on‐demand. The laser propulsion experiments employed a Hypersonic Shock Tunnel integrated with twin gigawatt pulsed Lumonics 620‐TEA CO2 lasers (∼ 1 μs pulses), to produce the required test conditions. This hypersonic campaign was carried out at nominal Mach numbers ranging from 6 to 10. Time‐dependent surface pressure distributions were recorded together with Schlieren movies of the flow field structure resulting from laser energy deposition. Results indicated laser‐induced pressure increases of 0.7–0.9 bar with laser pulse energies of ∼ 170 J, o...

Beam‐Riding Behavior of Lightcraft Engines with ∼ 1 μs Pulsed TEA CO2 Laser

The beam‐riding and angular impulse performance of four laser propulsion engine geometries were measured using a twin Lumonics K922M pulsed TEA CO2 laser system, with an Angular Impulse Measurement Device (AIMD). Airbreathing and solid ablative rocket (SAR) mode impulse data was collected to explore engine thrust‐vectoring behavior, as a function of: a) laser beam lateral offset from the engine axis of symmetry; b) laser pulse duration (∼ 50 ns spike with selectable 1.5 or 2.5 μs tail—depending upon laser gas mixture); and c) engine geometry (Lightcraft Type ♯150, ♯200, ♯250, and parabolic bell). Maximum airbreathing lateral momentum coupling coefficients (CM) up to 77 N‐s/MJ were achieved with the K922M laser; this represents a vast improvement over previous PLVTS laser (∼ 420 J, 18 μs duration) results which reached only 15 N‐s/MJ. Lateral CM performance of the ♯200 SAR Lightcraft engine was measured experimentally for the first time, using Delrin® propellant inserts.

Axial Impulse Generation of Lightcraft Engines with ∼ 1 μs Pulsed TEA CO2 Laser

A twin Lumonics K922M pulsed TEA CO2 laser system (∼50 ns FWHM spike, with selectable 1.5 or 2.5 μs tail—depending upon laser gas mixture) was employed to experimentally measure the axial impulse behavior of a family of lightcraft engine geometries, using a lightweight ballistic pendulum. Axial impulse performance in both airbreathing and solid ablative rocket (SAR) modes was examined as a function of: a) laser pulse energy (∼12 to 40 Joules); b) pulse duration (∼50 ns spike with 1.5 or 2.5 μs tail); and, c) engine geometry. The four engines under investigation were the Lightcraft Types ♯150, ♯200 and ♯250, and a 11 cm parabolic bell. Lightcraft ♯200 axial CM performance reached 250 N/MW, which is sharply higher than the 120 N/MW previously reported for the engine using long pulse (e.g., 10‐18 μs) CO2 electric discharge lasers.

Dedicated Laboratory Setup for CO{sub 2} TEA Laser Propulsion Experiments at Rensselaer Polytechnic Institute

Laser propulsion research progress has traditionally been hindered by the scarcity of photon sources with desirable characteristics, as well as integrated specialized flow facilities in a dedicated laboratory environment. For TEA CO2 lasers, the minimal requirements are time‐average powers of >100 W), and pulse energies of >10 J pulses with short duration (e.g., 0.1 to 1 μs); furthermore, for the advanced pulsejet engines of interest here, the laser system must simulate pulse repetition frequencies of 1–10 kilohertz or more, at least for two (carefully sequenced) pulses. A well‐equipped laser propulsion laboratory should have an arsenal of sensor and diagnostics tools (such as load cells, thrust stands, moment balances, pressure and heat transfer gages), Tesla‐level electromagnet and permanent magnets, flow simulation facilities, and high‐speed visualization systems, in addition to other related equipment, such as optics and gas supply systems. In this paper we introduce a cutting‐edge Laser Propulsion La...

Experimental Investigation of Axial and Beam-Riding Propulsive Physics with TEA CO{sub 2} laser

A twin Lumonics K922M pulsed TEA CO 2 laser system (pulse duration of approximately 100 ns FWHM spike, with optional 1 μs tail, depending upon laser gas mix) was employed to experimentally measure both axial thrust and beam‐riding behavior of Type ♯200 lightcraft engines, using a ballistic pendulum and Angular Impulse Measurement Device (AIMD, respectively. Beam‐riding forces and moments were examined along with engine thrust‐vectoring behavior, as a function of: a) laser beam lateral offset from the vehicle axis of symmetry; b) laser pulse energy (∼12 to 40 joules); c) pulse duration (100 ns, and 1 μs); and d) engine size (97.7 mm to 161.2 mm). Maximum lateral momentum coupling coefficients (C M ) of 75 N‐s/MJ were achieved with the K922M laser whereas previous PLVTS laser (420 J, 18 μs duration) results reached only 15 N‐s/MJ—an improvement of 5x. Maximum axial C M performance with the K922M reached 225 N‐s/MJ, or about ∼3x larger than the lateral C M values. These axial C M results are sharply higher than the 120 N/MW previously reported for long pulse (e.g., 10–18 μs) CO 2 electric discharge lasers.

Airbreathing Hypersonic Laser Thermal Propulsion Experiments with a LightCraft Vehicle - Status Update

A laser-propelled transatmospheric vehicle experiences the full spectrum of flight regimes, from subsonic to hypersonic, along its Earth-to-Orbit (ETO) trajectory. A 2-D model of a laser propelled LightCraft was tested in the T3 Hypersonic Shock Tunnel (HST) at the Henry T. Nagamatsu Laboratory for Aerothermodynamics and Hypersonics. The test campaign began with no flow, ambient (1 bar) conditions, and transitioned to medium enthalpy HST runs at Mach number of 9.0. The model was instrumented with piezoelectric pressure transducers to measure the time dependent pressure distributions. A high speed digital Schlieren imaging system recorded the time-dependent flowfield evolution inside the LightCraft absorption chamber, following pulsed laser energy deposition. This data was also compared with blast wave arrival at numerous pressure transducers distributed along the 2D engine centerline. A Lumonics TEA 622 laser system with an unstable resonator cavity emitted 1 μs, 200 J pulses (low divergence, 90ns FWHM) into the 0.6 m diameter HST test section.