Changing debris orbits using High Power Pulsed Laser Interaction (HP PLI) finds interest in the Low-Earth Orbit (LEO) due to space debris congestion. Laser facilities allowing both high energy and repetition rate of a short pulsed irradiation become available as provided by the high power HiLASE beamline facility (Prague, CZ) with BIVOJ (100J, 10ns, 10Hz, 1030nm). In order to illustrate such an application, originally Crookes radiometer concept was adapted to quantify the efficiency of repeated laser shots in increasing rotating speed according to laser matter interaction. Various materials, from model to space applicative materials, allowed to estimate the material response with various irradiation characteristics (single shots vs. repeated shots). Matter behaviors (ablation, cratering, spallation, perforation) bracketed the laser conditions suitable in the perspective of laser propulsion with limited creation of extra debris or irradiated structures damages. Next is to strengthen the robustness of the simulation/experiment dialog to use simulation as a predesign tool for laser space propulsion.
Small (1-10cm) debris in low Earth orbit (LEO) are extremely dangerous, because they spread the breakup cascade depicted in the movie “Gravity.” Laser-Debris-Removal (LDR) is the only solution that can address both large and small debris. In this paper, we briefly review ground-based LDR, and discuss how a polar location can dramatically increase its effectiveness for the important class of sun-synchronous orbit (SSO) objects. No other solutions address the whole problem of large (~1000cm, 1 ton) as well as small debris. Physical removal of small debris (by nets, tethers and so on) is impractical because of the energy cost of matching orbits. We also discuss a new proposal which uses a space-based station in low Earth orbit (LEO), and rapid, head-on interaction in 10- 40s rather than 4 minutes, with high-power bursts of 100ps, 355nm pulses from a 1.5m diameter aperture. The orbiting station employs “heat-capacity” laser mode with low duty cycle to create an adaptable, robust, dualmode system which can lower or raise large derelict objects into less dangerous orbits, as well as clear out the small debris in a 400-km thick LEO band. Time-average laser optical power is less than 15kW. The combination of short pulses and UV wavelength gives lower required energy density (fluence) on target as well as higher momentum coupling coefficient. This combination leads to much smaller mirrors and lower average power than the ground-based systems we have considered previously. Our system also permits strong defense of specific assets. Analysis gives an estimated cost of about $1k each to re-enter most small debris in a few months, and about 280k$ each to raise or lower 1-ton objects by 40km. We believe it can do this for 2,000 such large objects in about four years. Laser ablation is one of the few interactions in nature that propel a distant object without any significant reaction on the source.
The application of energetic polymers has resulted in an increased thrust in micro laser plasma thrusters compared to
standard polymers. In this study we tested a novel concept for micro laser plasma thrusters, i.e. the application of liquid
polymeric fuels, by using polymer solutions of the energetic materials with different viscosity. Shadowgraphy
experiments suggest that for higher viscosity solutions ablation without splashing is possible, indicating that liquids are
applicable as fuels in laser plasma thrusters. First thrust measurements on a viscous polymer solution confirmed this by
yielding a specific impulse similar to a solid material.
The AEgis Technologies Group and RTI International are developing microsensors for High Energy Laser (HEL)
diagnostic applications. The conformal sensor array will measure the irradiance profile of an incident laser beam, and
concomitant rise in surface temperature of the target. The open mesh architecture allows 90% of the beam to impact the
surface. A critical part of this program is developing a protective coating that ensures sensor survivability at high
irradiance levels for operational lifetimes on the order of 10 seconds. The protective coating must transmit a measurable
amount of light to the irradiance sensor. We have conducted experiments to evaluate candidate heat shield materials.
In the first round of experiments, a 10kW CO2 laser was used to irradiate pure materials, including metals and carbon
foils. Although many of the metal foils were perforated by the laser, no significant amount of material was ablated
away. In fact, most of the test samples gained mass, presumably due to oxidation. Analysis of high speed video shows
that once the metal melted, surface tension caused the molten metal to coalesce into droplets around the rim of the hole.
The second and third rounds of testing, conducted with a 3kW, 1.07μm fiber laser, included samples of highly reflective
metals and ceramics, standard plasma-sprayed coatings, and multilayer stacks. We have also measured the performance
of temperature sensors and irradiance sensors fabricated from nanoparticle solutions deposited by advanced printing
technology and have completed a preliminary investigation of high temperature adhesives.
Recently we became interested in applying previous work with liquid fueled laser powered minithrusters for
spacecraft orientation to the conceptual design of a multi-newton thruster based on the same principles. Solid-fuel
configurations (such as the fuel tapes used in the Photonic Associates microthruster) are not amenable to the
range of mass delivery rates (g/s to g/s) necessary for such an engine.
We will discuss problems for this design which have been solved, including identifying a practical method of
delivering liquid fuel to the laser focus, avoiding splashing of liquid fuels under pulsed laser illumination, and
avoiding optics clouding due to ablation backstreaming on optical surfaces from the laser-fuel interaction region.
We have already shown that Isp = 680 seconds can be achieved by a viscous liquid fuel based on glycidyl azide
polymer and an IR-dye laser absorber.
The final problem is mass: we will discuss a notional engine design which fits within a 10-kg "dry mass"
budget. This engine, 80kg mass with fuel, is designed to fit within a 180-kg spacecraft, and use 3kW of prime
power to deliver a Δv of 17.5 km/s to the spacecraft in sixteen months. Its specific impulse will be adjustable
over the range 200sp<3,600 seconds and maximum thrust will be 6N, based on performance which has been
demonstrated in the laboratory. Such an engine can put small satellites through demanding maneuvers in short
times, while generating the optimum specific impulse for each mission segment. We see no reason why
Isp = 10,000 seconds cannot be achieved with liquid fuels.
In this paper, we review the history of laser space propulsion from its earliest theoretical conceptions to modern practical applicatons. Applications begin with the "Lightcraft" flights of Myrabo and include practical thrusters for satellites now completing development as well as proposals for space debris removal and direct launch of payloads into orbit. We consider laser space propulsion in the most general sense, in which laser radiation is used to propel a vehicle in space. In this sense, the topic includes early proposals for pure photon propulsion, laser ablation propulsion, as well as propulsion using lasers to detonate a gas, expel a liquid, heat and expel a gas, or even to propagate power to a remote conventional electric thruster.
In this paper, we review the history of laser space propulsion from its earliest theoretical conceptions to modern practical applicatons. Applications begin with the "Lightcraft" flights of Myrabo and include practical thrusters for satellites now completing development as well as proposals for space debris removal and direct launch of payloads into orbit. We consider laser space propulsion in the most general sense, in which laser radiation is used to propel a vehicle in space. In this sense, the topic includes early proposals for pure photon propulsion, laser ablation propulsion, as well as propulsion using lasers to detonate a gas, expel a liquid, heat and expel a gas, or even to propagate power to a remote conventional electric thruster. We also discuss the most recent advances in LSP. For the first time, it is possible to consider space propulsion engines which exhibit thrust of one to several newtons while simultaneously delivering 3,000 seconds, or greater, specific impulse. No other engine concept can do both in a compact format. These willl use onboard, rather than remote, lasers. We will review the concept of chemically augmented electric propulsion, which can provide overall thrust efficiency greater than unity while maintaining very low mass to power ratio, high mean time to failure and broad operating range. The main advantage of LSP is exhaust velocity which can be instantaneously varied from 2km/s to 30km/s, simply by varying laser pulsewidth and focal spot size on target. The laser element will probably be a diode-pumped, fiber master-oscillator-power-amplifier (MOPA) system. Liquid fuels are necessary for volumetric efficiency and reliable performance at the multi-kW optical power levels required for multi-N thrust.
The micro laser plasma thruster (μLPT) is a micro propulsion device, designed for the steering and propelling of small satellites (1 to 10 kg). A laser is focused onto a polymer layer on a substrate to form a plasma. The thrust produced by this plasma is used to control the satellite motion. To understand the influence of the specific properties of the polymers, three different "high"- and "low"-energetic polymers were tested: poly(vinyl chloride) (PVC) as a low-energetic reference polymer that showed the best properties among commercial polymers, a glycidyl azide polymer (GAP), and poly(vinyl nitrate) (PVN) as high-energetic polymers. It was necessary to dope the polymers with carbon nanoparticles or an IR-dye to achieve absorption at the irradiation wavelength in the near IR. Decomposition into smaller fragmentation was measured for the energetic polymers than for PVC corresponding well to the higher momentum coupling coefficient of the energetic polymers, which indicates that more thrust can be gained from a chosen incident laser power. The measurements of the kinetic energies of selected decomposition fragments revealed no significant difference between the different carbon doped polymers. Only for GAP with the IR-dye a change in the ratio between ions with different kinetic energy was observed with increasing fluence. More C+ ions with higher kinetic energy were detected at higher fluences. No correlation between the kinetic energies of the ablation products and the specific impulse could be established for the obtained data.
The micro laser plasma thruster (μLPT) is a micropropulsion device, designed for the steering and propelling of small satellites (10 to 100 kg). A diode laser is focused on a two-layer polymer tape, where it forms a plasma. The thrust produced by this plasma is used to control the satellite motion. Three different polymers (GAP, PVN and PVC) doped with carbon and/or IR-dye were investigated for their performance as fuel polymer. The different dopants for GAP seem to have only little influence in the ablation properties. The most pronounced differences are observed in the fragment ejection detected in the shadowgraphy measurements and the crater appearance. For all carbon doped polymers, the ablation spots have a similar rough morphology. The shadowgraphy measurements of PVN reveal, that the shockwave and particle plume propagates faster as in the case of the other polymers. The particle plumes showed a very different expansion behavior for all polymers, whereas the plasma temperature and electron density measurements showed no significant difference. Only PVC displayed a slower almost linear drop of the plasma temperature over time. The thrust measurements showed the best results for GAP.
For the first time, we have measured the momentum coupling coefficient and plasma expansion velocity (specific impulse) in the femtosecond region, over a laser intensity range from ablation threshold to thirty times threshold. These measurements extend the laser pulsewidth three orders of magnitude relative to previous reports. We studied several pure metals and three organic compounds as targets. The organic compounds were exothermic polymers specifically developed for the micro-laser plasma thruster, and two of these used "tuned absorbers" rather than carbon particles for the laser absorption function. The metals ranged from Li to W in atomic weight. We measured time of flight profiles for ions and found dramatic two-temperature distributions for some conditions. Specific
impulse reached record values for this type of measurement and ablation efficiency was near 100%.
Space debris constitutes a significant hazard to low earth orbit satellites and particularly to manned spacecraft. A quite small velocity decrease from vaporization impulses is enough to lower the perigee of the debris sufficiently for atmospheric drag to de-orbit the debris. A short pulse (picosecond) laser version of the Orion concept can accomplish this task in several years of operation. The "Mercury" short pulse Yb:S-FAP laser being developed at LLNL for laser fusion is appropriate for this task.
The range and maturity of commercially useful laser applications are illustrated by selected examples. Macroscopic applications (commercialized or potentially so in the near future) include cutting, machining and welding metals, cutting fabrics, shock hardening of steels, nitrogenization of iron, and laser drilling through rock. Microscopic applications include drilling micro-holes for cooling of jet engine turbine blades, thin film growth, precision machining of structures inside transparent materials and inertially-confined deuterium-tritium fusion. To be commercially useful, these applications take advantage of the special properties of laser light, such as monochromaticity, high brightness, high pulse energy or intensity, wavelength range from soft xray to far infrared and pulse duration from femtoseconds to CW. This talk will be divided into three sections: (a) summary of the theory of laser-materials interactions with examples from published laser impulse production studies, (b) macroscopic applications, (c) microscopic applications and (d) exotic and futuristic applications, including a diode-laser-driven μN thruster for micro- and nano-satellites, and proposals to use lasers to clean hundreds of thousands of small but hazardous space debris from near-Earth space and to launch 5kg payloads into near-Earth orbit.
We have developed a new type of miniature jet for pointing microsatellites. It is based on laser ablation produced by a multi-mode diode laser. The target is a specially prepared tape with a transparent layer through which the laser light passes and an absorbing layer which produces the thrust. We have achieved specific impulse up to 1000 seconds (greater than possible with chemistry), together with laser momentum coupling coefficients of order 6 dyne/W. The preprototype should achieve 100 dynes of thrust. We will discuss the target interaction physics, the materials science involved in creating the targets, and some of our measurements with the preprototype thruster.
The laser plasma thruster (LPT) is a new microthruster for small satellites. We report on development and testing of a prototype LPT. Some advantages of the LPT are: thruster voltage 4 V, mass less than 1 kg, power-to-thrust ratio 10 kW/newton and Isp up to 1000 seconds. Typical thrust level is 250 (mu) N with PVC fuel. Thrust of 1 mN is expected with energetic fuel. The pre-prototype continuous thrust experiment includes the laser mount and heat sink, lens mounts, and focusing mechanism, which are coupled to the target material transport mechanism. The target material is applied to a transparent plastic tape, and the laser is focused on a series of tracks on the tape. The tape drive hardware and laser drive electronics, are described, as well as the control and diagnostic software. Design, construction, and calibration of the thrust stand are described. During continuous operation, the exhaust plume is deflected in the direction of the moving tape. When the laser is operated in pulsed mode, the exhaust plume is perpendicular to the tape (parallel to the optical axis). This provides some thrust vector control.
The ablation characteristics of various polymers were studied at low and high fluences. The polymers can be divided into three groups, i.e. polymers containing triazene groups, designed ester groups, and reference polymers, such as polyimide. The polymers containing the photochemically most active group (triazene) exhibit the lowest threshold of ablation (as low as 25 mJ cm-2) and the highest etch rates (e.g. 250 nm/pulse at 100 mJ cm-2), followed by the designed polyesters and then polyimide. Neither the linear nor the effective absorption coefficients reveal a clear influence on the ablation characteristics. The different behavior of polyimide might be explained by a pronounced thermal part in the ablation mechanism. The laser-induced decomposition of the designed polymers was studied by nanosecond interferometry and shadowgraphy. The etching of the triazene polymer starts and ends with a laser pulse, clearly indicating photochemical etching. Shadowgraphy reveals mainly gaseous products and a pronounced shockwave in air. The designed polymers were tested for applications ranging from microoptical elements to polymer fuel for laser plasma thrusters.
Laser supported propulsion of a micro-airplane with water-covered ablator is demonstrated. The repetitive use of overlay structure is experimentally demonstrated with specially-designed water supply. The various transparent overlay is investigated by the CIP-based hydrodynamic code and experiments by pendulum and semi-conductor load cell. The momentum coupling efficiency of 5000 N-sec/MJ has been achieved by ORION experiments that agree with the simulation code. With the maximum efficiency approximately 105 N- sec/MJ predicted by the simulation, 30 pulses of MJ laser can give the sound speed to 10tons airplane. The concept can also be used for driving a micro-ship inside human body and a robot under the accidental circumstance of nuclear power reactor in which large amount of neutron source makes electronic device useless.
We present results of computer simulations of the launch through the atmosphere of a cone-shaped flyer which demonstrate that laser ablation rockets, using a 1MW ground-based laser, can lift 6kg payloads into low earth orbit. We discuss optimization of delivered mass, mass ratio and energy cost.
This report briefly reviews the development, capabilities, and current status of pulsed high-power coherent CO2 laser radar systems at the Maui Space Surveillance System (MSSS), HI, for acquisition, tracking, and sizing of orbiting objects. There are two HICLASS systems, one integrated to the 0.6 m Laser Beam Director and one just integrated Summer 2000 to the 3.7 m Advanced E-O System (AEOS). This new system takes full advantage of the large AEOS aperture to substantially improve the ladar range and sensitivity. These improvements make the AEOS HICLASS system potentially suitable for tracking and characterization experiments of small < 30 cm objects in low-earth-orbits.
Approximately ideal flight paths to low-Earth orbit (LEO) are illustrated for laser-driven flights using a 1-MW Earth-based laser, as well as sensitivity to variations from the optima. Different optima for ablation plasma exhaust velocity VE, specific ablation energy Q*, and related quantities such as momentum coupling coefficient Cm and the pulsed or CW laser intensity are found depending upon whether it is desired to maximize mass m delivered to LEO, maximize the ratio m/M of orbit to ground mass, or minimize cost in energy per gram delivered. A notional, cone-shaped flyer is illustrated to provide a substrate for the discussion and flight simulations. Our flyer design conceptually and physically separates functions of light collection, light concentration on the ablator, and steering. All flights begin from an elevated platform. Flight simulations use a detailed model of the atmosphere and appropriate drag coefficients for sub- and supersonic flight in the continuum and molecular flow regimes. A 6.2-kg payload is delivered to LEO from an initial altitude of 35 km with launch efficiencies approaching vacuum values of about 100 kJ/g.
The micro laser plasma thruster ((mu) LPT) is an efficient, long- life, low-thrust pulsed rocket engine which uses a high-brightness semiconductor or glass fiber laser as a source of energy. It uses a simple, low-voltage semiconductor switch to drive the laser, resulting in zero off-state electrical power. Results are presented of the first experimental demonstration of uLPT's. We measured single impulses covering 5 orders of magnitude from 40 micro dyn-s [< 1 nano newton-s] to 2 dyn-s, specific impulse up to 1,800 seconds and coupling coefficients up to 25 dyne-s/J. Several target materials were studied. Initial applications are orientation and re-entry at end of life for micro- and nanosatellites. Anticipated lifetime output of the prototype engine now under development is about 5E7 dyn-s [500 newton-s], sufficient to re-enter a 5 kg LEO satellite.
Results are presented of the first measurements of laser-ablation impulse on structured targets of the modified Fabbro type in which impulse coupling coefficients Cm up to 500 dyne-s/J were obtained for 85-ns duration laser pulses by direct measurement with momentum pendula. Our target design generated these Cm values for single-pulse laser fluence of 1.2 J/cm2 and peak intensity 14 MW/cm2, an order of magnitude below the intensity at which similar coupling has been observed before. This result is important for the ORION demonstration, since it effectively closes a factor- of-20 deficit between presently available projected intensity at 300 km range and the intensity required for optimum coupling to standard materials. The Nd:glass laser employed in these measurements had 1.05 micrometer wavelength and pulse duration from 25 to 100 ns. Ambient pressure was less than 10 millitorr. Impulse coupling data on water ice, stone, carbon phenolic, PMMA and other materials were also obtained, for cross-calibration and because of interest in applications to 'uncooperative' natural bodies in space. We discuss the significance of these results for planning a laser propulsion demonstration in space, as well as possible extensions which could yield appropriate Cm for repetitively- pulsed propulsion of objects into low Earth orbit (LEO).
ORION is a practical proposal for removing the 150,000 pieces of manmade space debris in the 1- to 10-cm size range now orbiting the Earth below 1500 km altitude which threaten large space systems in low Earth orbit. It is based on using the thrust produced by pulsed laser ablation of a thin layer on the debris surface to drop its perigee sufficiently for reentry and burnup. Applied when the object is rising between about 45 and 15-degree zenith angle, the necessary (Delta) v is of order 100 m/s. A laser of 30 kW average power at 10-ns pulsewidth and a 6-m mirror with adaptive optics can clear near-Earth space of these debris in 2 years of operation. Technical challenges faced by such a system include: heavy demands on detection, tracking and adaptive optics arising from the tiny optical cross section of the smallest debris and the required pointing accuracy and steering rate, stimulated Raman conversion and nonlinear refraction of the laser beam in the atmosphere, uncertainty of momentum coupling coefficients (Cm) for some materials, and high-average-power laser development. It is crucial that the system we propose be developed under international aegis, to insure that its installation does not increase international tensions. It should be viewed as a single-pay lifetime insurance policy for the World's space assets whose premium is less than 1% of the protected asset value, an excellent rate for such contracts.
Our measurements of laser coating removal rate for 14- micrometer-thick black organic paint coatings on a refractory substrate showed the rather astonishing result that total exposure time (Delta) t required to ablate the coating (for these particular thin organic coatings, in air) is described by (Delta) t equals C X I-3/2 sec where x is the coating thickness, I the incident pulse intensity (W/cm2) and the constant C equals 1.4 X 107 W3/2-s/cm4. This was true for wavelength 350 nm less than (lambda) less than 10.6 micrometer and incident intensity 81 W/cm2 less than I less than 424 MW/cm2, covering a 7-order-of- magnitude. Such a simple result is phenomenal because of the range of different physical processes known to be involved (simple boiling, thermal conduction and differential thermal expansion for the long pulses, but the combined effects of shock spallation, large excursions within the solid equation of state, and acceleration, compression, shocking, thermal conduction, radiation, phase explosion and even some ionization for the shortest pulses). If extensible to other coatings and substrates, it is also very valuable for the design of expensive laser coating removal facilities, which are now receiving strong interest for very large-scale decontamination and aircraft repainting. Our first-order parametric model fits the experimental results to within better than a factor-of-3 in laser intensity throughout the above range.
Nearly 200,000 pieces of debris in the 1 - 20 cm range in low- Earth orbit (LEO), a legacy of 35 years of spaceflight now threaten long-term space missions. An economical solution to the problem is to use a ground-based laser to create a photoablation jet on the objects and cause them to re-enter the atmosphere and burn up. A sensitive optical detector is required to locate objects as small as 1 cm at 1500 km range. Applied when the object is rising and between about 45 and 15- degree zenith angle, the necessary (Delta) v is of order 100 m/s. A laser of 30 kW average power at 5-ns pulsewidth and a 4 - 6 m mirror with adaptive optics can clear near-Earth space of the 1-20-cm debris in 2 years of operation. A high altitude site minimizes turbulence correction, interference from nonlinear optical effects, and absorption. We discuss the effect of nonlinear optical processes in the atmosphere as boundaries on propagation, and how to choose system parameters to guarantee optimum conversion of laser energy to target momentum. The laser might be Nd:glass (1.06 micrometer/530 nm), or iodine (1.3 micrometer).
Laser impulse space propulsion (LISP) has become an attractive concept, due to recent advances in gas laser technology, high-speed segmented mirrors, and improved coefficients for momentum coupling to targets in pulsed laser ablation. There are numerous specialized applications of the basic concept to space science -- ranging from far-future and high capital cost to the immediate and inexpensive, such as: LEO-LISP (launch of massive objects into low-Earth-orbit at dramatically improved cost-per-kg relative to present practice); LEGO-LISP (LEO to geosynchronous transfers); LO-LISP (periodic re-boost of decaying LEO orbits); and LISK (geosynchronous satellite station-keeping). It is unlikely that one type of laser will be best for all scenarios. In this paper, we discuss these most immediate applications, leaving LEO-LISP -- the application requiring the longest reach -- for another venue.
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