JP2010275929A - Laser propulsion system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser propulsion system achieving high specific thrust rocket engine without limit in combustion chamber temperature, pressure, and space charge density, achieving variability of thrust and specific thrust, and enabling free flight not in a corded style such as a kite. <P>SOLUTION: This system includes a semiconductor laser, a beam change over switch connected to the semiconductor laser, a Q switch solid pulse laser connected to the beam change over switch, and a power source supplying electric power to the semiconductor laser. The system changes over an operation mode between a first operation mode for executing continuous irradiation of beam to water or steam by the semiconductor laser and a second operation mode for executing pulse irradiation of the beam to water or steam by the Q switch solid pulse laser based on excitation of the semiconductor laser, by the beam change over switch. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laser propulsion system, and particularly to a propellant structural material that uses a liquid and a gas that are not flammable as propellants, and uses a heated jet gas generated by directly irradiating the propellant with a laser as a propulsive force. The present invention relates to a high-performance (high specific force) laser propulsion system that is not limited.

  The existing space propulsion systems, namely chemical rocket propulsion, electric propulsion (ion thruster, MPD thruster, hall thruster, arc jet thruster), laser propulsion, and nuclear propulsion, all have momentum thrust (reaction thrust) by injection to the rear of the mass. Is the driving principle.

  In recent years, in addition to chemical rockets, electric propulsion and laser propulsion have been put into practical use as well as research and development. In electric propulsion, ion thrusters have already been used for attitude control of satellites, and microwave discharge ion thrusters have been installed on the Hayabusa spacecraft in Japan's JAXA ISAS asteroid sample return program. There is a track record. Another promising propulsion system candidate is laser propulsion.

  R & D on the practical application of laser propulsion is a 71m vertical flight with acceleration of 2.3G by CO2 laser air breathing pulse detonation laser method by Mirabor and Franklin Mead project of Edwards Air Force Laboratory in July 1999 Has succeeded.

  In general, a rocket propulsion device accelerates a propellant into a high-speed fluid to obtain a large propulsive force with a small amount of propellant. In chemical rocket propulsion as a method for realizing this, a propellant is burned to a high temperature in a combustion chamber to increase the pressure, and this is injected from a nozzle to convert thermal energy into kinetic energy to obtain propulsive force. Hereinafter, “propulsive force” is described as “thrust force” that is normally used.

  In order to generate high-speed propellant gas, the combustion chamber needs to be made of a material that can withstand high temperatures and high pressures, and peripheral devices must also satisfy requirements corresponding thereto. In addition, in chemical rockets, the amount of energy generated per fuel mass is determined in principle, and there is an upper limit of specific thrust. Gaseous fuel (hydrogen, oxygen, etc.) at room temperature requires enormous energy for storage, and the firing timing depends on the fuel injection. Basically, an oxidizer and a fuel are required, a complicated technique is required for storage, and the mixing ratio needs to be controlled. Solid rockets are relatively stable, but thrust adjustment after ignition is difficult and reignition is difficult.

  In the electric propulsion method, an electric field is applied to the charged particles generated by discharge and the like to accelerate and generate a high-speed jet gas, eliminating the need for a high-temperature and high-pressure combustion chamber. Has a limit due to space charge limitation, and there is a limit to the thrust that can be generated against the engine caliber. An engine mounted on a spacecraft cannot generate a large propulsive force because its diameter is limited.

  In addition, most laser propulsion currently being researched and developed assumes a string-like system that is propelled by the ground source laser source and power source without loading the aircraft with a laser source and power source. is doing. The advantage of laser propulsion is often described as the advantage that no energy source is required, which is rather a fatal drawback for a free-flying spacecraft. Just as a fighter with a string like a kite does not work at all, a laser-propelled spacecraft needs a self-supporting system that is equipped with both a laser source and a power source for power.

  The conventional laser propulsion system irradiates water or ice from an external orbital aircraft (aircraft placed above the equator) on water or ice on an orbit around the earth, and obtains thrust by plasma injection. (For example, refer to Patent Document 1).

  In addition, there is a laser that supplies a thrust to a thrust generation device through a wired device such as an optical fiber and obtains a thrust by plasma injection (for example, see Patent Document 2).

JP 2001-132542 A (page 2-4, FIG. 1) JP 2003-148247 A (page 2-5, FIG. 1)

  None of the conventional laser propulsion systems described above has a laser source or power supply mounted on the fuselage, that is, the laser beam transmitted from the outside, such as an aircraft on the ground or the equator, is condensed into a propellant. Since it is irradiated and gains propulsive power, it has the disadvantage that it cannot fly freely with a stringed system like a kite.

In addition, the method using a chemical fuel as a propellant has a drawback that a rocket engine with a high specific thrust cannot be realized because it is limited to the combustion chamber temperature and pressure.
The object of the present invention is to realize a rocket engine with a high specific thrust without being limited by the combustion chamber temperature and pressure, and to realize a variable thrust and a specific thrust, and can fly freely instead of a stringed system such as a kite. It is to provide a laser propulsion system.

  The first laser propulsion system of the present invention is characterized in that an arbitrary propellant is heated by a laser, and thrust is generated using the kinetic energy of generated high-temperature and high-pressure steam.

According to a second laser propulsion system of the present invention, in the first laser propulsion system, the high-temperature and high-pressure steam directly absorbs laser energy and generates a thrust while suppressing a thermal load applied to the nozzle wall surface. It is a feature.

According to a third laser propulsion system of the present invention, in the first or second laser propulsion system, the laser as a heating source of the propellant operates by arbitrarily switching between continuous oscillation and pulse oscillation. It is said.

The fourth laser propulsion system according to the present invention is characterized in that, in the third laser propulsion system, the laser is a solid laser, a semiconductor laser, or a fiber laser used alone or in combination.

The fifth laser propulsion system of the present invention is characterized by including a laser source that uses water as fuel and irradiates the water with laser light, and a power source that supplies power to the laser source.

A sixth laser propulsion system according to the present invention is characterized by including water vapor that heats water, a laser source that irradiates the water vapor with laser light, and a power source that supplies power to the laser source.

The seventh laser propulsion system of the present invention is characterized by including a laser source that has water and water vapor, and irradiates one of them with a laser beam, and a power source that supplies power to the laser source.

An eighth laser propulsion system of the present invention is characterized in that, in the laser propulsion system according to any one of the fifth to seventh aspects, the laser source is a semiconductor laser.

The ninth laser propulsion system of the present invention is characterized in that, in any of the fifth to seventh laser propulsion systems, the laser source is a semiconductor laser excitation Q-switched solid state pulse laser.

A tenth laser propulsion system according to the present invention is the laser propulsion system according to any one of the fifth to seventh aspects, wherein the laser source includes a semiconductor laser and a semiconductor laser excitation Q-switched solid-state pulse laser, It is characterized by switching to the source.

An eleventh laser propulsion system according to the present invention is characterized in that, in any of the ninth and tenth laser propulsion systems, the solid-state laser is a YAG laser.

According to a twelfth laser propulsion system of the present invention, in any of the fifth to eleventh laser propulsion systems, the power source is a fuel cell.

A thirteenth laser propulsion system according to the present invention is characterized in that, in any of the fifth to eleventh laser propulsion systems, the power source includes a fuel cell and a solar cell.

A fourteenth laser propulsion system according to the present invention is characterized in that, in the twelfth or thirteenth laser propulsion system, the fuel cell is a polymer electrolyte fuel cell.

The fifteenth laser propulsion system of the present invention is
With semiconductor lasers;
A beam changeover switch connected to the semiconductor laser;
A Q-switched solid state pulse laser connected to the beam changeover switch;
A power supply for supplying power to the semiconductor laser;
And a second operation mode in which the propellant is pulsed by the Q-switched solid-state pulse laser based on the excitation of the semiconductor laser. It is characterized by switching.

According to a sixteenth laser propulsion system of the present invention, in the fifteenth laser propulsion system, the propellant is water vapor, water, or ice.

The seventeenth laser propulsion system of the present invention is characterized in that, in any one of the fifteenth and sixteenth laser propulsion systems, the solid-state laser is a YAG laser.

An eighteenth laser propulsion system according to the present invention is characterized in that in the laser propulsion system according to any one of the fifteenth to seventeenth aspects, the power source includes one or both of a fuel cell and a solar cell.

According to a nineteenth laser propulsion system of the present invention, in the eighteenth laser propulsion system, the fuel cell is a solid polymer fuel cell.

A twentieth laser propulsion system of the present invention is characterized by a spacecraft or an aircraft equipped with any one of the first to nineteenth laser propulsion systems.

  As described above, the laser propulsion system according to the present invention can be equipped with a laser source that irradiates water or water vapor with a laser and a power source that supplies power to the laser source. Yes.

Further, since there is no limitation on the combustion chamber temperature, pressure, and space charge density, it has the effect of realizing a rocket engine with high specific thrust and variability of thrust and specific thrust.

It is a figure which shows the relationship between a laser output and driving force. It is a system block diagram showing one embodiment of a laser propulsion system of the present invention. It is a block diagram which shows an example of the semiconductor power laser excitation Q switch YAG laser of FIG. It is explanatory drawing which shows the laser irradiation to heating water vapor | steam. It is explanatory drawing which shows laser irradiation to water. It is a general-view figure which shows the spacecraft carrying a laser propulsion system.

  The basic principle of laser propulsion utilizes the reaction force of high-temperature gas or ion ejection caused by laser irradiation. When the material is irradiated with a laser, the material melts and evaporates. In this evaporation, particles melted in the direction opposite to the laser irradiation direction scatters backward, and a reaction thrust is generated. This is equivalent to rocket injection and is the same propulsion principle with the same momentum thrust as the rocket.

  There are two types of laser propulsion systems. First, a propellant that uses a low molecular weight substance such as hydrogen as a propellant, and achieves a high specific thrust with a high-power pulse laser. Second, a relatively large molecular weight substance such as water is used as a propellant. This is a propulsion method that achieves high thrust with a laser.

In laser propulsion technology, it becomes possible to give an arbitrary energy density to the propellant by a combination of laser light and propellant, and the propellant exhaust speed and fluid motion state can be controlled.
There are two important performance indicators for thrust generation in laser propulsion. Laser propulsion specific momentum coupling coefficient C _m (Momentum coupling
coefficient: N · s / J = N / W) and a specific impulse I _SP to be used in the normal propulsion. The momentum coupling coefficient C _m is the thrust power ratio (N / kW) in electric propulsion. In a propulsion system that uses momentum thrust as the propulsion principle, the following relational expression is important: thrust F (N), input power P, and propulsion efficiency η that indicates how much this input power P is converted into kinetic energy of the propellant It is. Since laser propulsion is used, the laser power P _L (W) is used. Here, g is the acceleration of gravity, m (kg / s) is the propellant flow rate, and V _E (m / s) is the scattering rate (propellant flow rate) of the ablated material.
(1)
The momentum coupling coefficient C _m is defined as the ratio of the momentum of the evaporated substance due to ablation generated on the target surface to the laser energy to the target, and is in the range of 1 to 100 dyne · s / J (dyne / W = 10N / MW). The It can also be interpreted as the thrust generated per unit of laser power.
(2)
Specific thrust Isp is defined by the following equation.
(3)
The following holds for the energy balance per unit time in laser propulsion.
(Four)
η is the irradiation laser energy P _L is the kinetic energy of the propellant
The percentage converted to is shown. Equation (5) is obtained from equations (2), (3), and (4).
(Five)
(5) the product of C _m and I _SP of formula represents the fluid efficiency. The performance of laser propulsion can be controlled with the upper limit of the conversion efficiency (fluid efficiency) from laser energy to plasma kinetic energy.

On the other hand, it depends only on the speed V _E of the propellant specific impulse I _SP from equation (3). If the fluid efficiency (2η / g) is determined, C _m and _ISP are inversely proportional to each other according to the equation (5), so that it is possible to trade off C _m and _ISP . In other words, the laser power and the utilization efficiency of the propellant can be traded off.

For example, a propulsion system that produces a large thrust with respect to laser power (a large amount of propellant is used to obtain a large C _m ) and a propulsion system that produces a large specific thrust (a large _ISP ) (thrust with a small amount of propellant) Show that the propulsion system can design laser propulsion while reflecting actual conditions. That is, high I _SP or with reduced propellant consumed by the control of the propellant exhaust velocity, selection of high C _m becomes possible to obtain a large thrust. Propellant saving mode of high I _SP is ideal for use to transition or planetary missions from orbit to geosynchronous orbit.

The laser propulsion of the present invention can use a stable and inexpensive substance such as water without requiring a highly chemically active oxidizing agent or reducing agent as a fuel (propellant). In addition, the exhaust gas is water vapor that has no impact on the global environment, and it is highly meaningful to develop it as a propulsion system for future aerospace vehicles. Laser propulsion is a technology for generating thrust by converting thermal energy applied to a propellant into kinetic energy using the high power density (light intensity) property of a laser.

Compared to conventional propulsion systems based on chemical combustion, laser propulsion allows you to freely select the propellant's thermal energy (temperature) and kinetic energy, making it easier to design engine performance according to the purpose of the propulsion system. . A large laser power or a small laser power can be arbitrarily applied to the target. In addition, since a material (such as water) that can be easily handled can be used for the fuel, it is considered that the reliability and ease of handling of the propulsion system can be improved and the cost can be reduced.

In previous laser propulsion research, various propellants were irradiated with laser in the laboratory, and basic data such as propulsive force generated against incident laser power and jet gas velocity were measured. As a result, the gas ejection speed can be changed from 100m / s to 40m depending on the combination of laser irradiation power density (condensing method) and propellant.
It can be confirmed that the laser propulsion system can be changed up to km / s, which indicates that the laser propulsion system can be applied to various applications, and basic data necessary for the design of the propulsion system has been acquired.

FIG. 1 is a table summarizing experimental data showing the relationship between laser power and propulsive force. Figure 1 shows the formula (1)
Looking for a match.
The parameters efficiency η and specific thrust Isp are the ratio (kinetic energy conversion rate) and specific thrust (propellant jet gas velocity ÷ gravity acceleration, unit = second) at which laser energy is converted into propellant kinetic energy, respectively. The blue line in Fig. 1 is a condition comparable to the performance obtained by burning liquid oxygen + liquid hydrogen such as an HII-A rocket with a specific thrust of 600 seconds using water as a propellant. The line shown in red uses metal as a propellant and has a specific thrust of 3000 seconds, which is comparable to the performance of an ion engine adopted by Hayabusa (JAXA).

A system operating in a mode with a low specific thrust for a given laser power will produce a larger thrust (but consume more propellant). Further, when the specific thrust is about 3000 seconds, the jet gas is plasma, and the radiation loss causes the energy conversion rate to decrease.

As a laser used as an energy source, a semiconductor laser (LD) whose output has been increasing in recent years despite its small size is suitable as a spacecraft-mounted type. A semiconductor laser basically has continuous oscillation and is suitable for generating a jet gas having a relatively low specific thrust. On the other hand, in order to obtain a high specific thrust, a pulse operation type laser device that generates a high peak pulse is suitable. In order to realize this condition, a solid-state laser (Nd: YAG or the like) using a semiconductor laser as an excitation source and added with a Q switch is technically suitable.

In the present invention, water, ice, water vapor or the like is used as a propellant. The advantage of using water vapor compared to water (liquid) is that it can create a high temperature (high pressure) with high energy efficiency. Since a large amount of power can be concentrated on a small mass (molecule), the temperature can be increased. In other words, if water vapor is used, the density will be about one-thousandth of water, so if laser power is injected into the same volume, water vapor will have a higher temperature and Isp will increase.

Furthermore, the advantage of using a combination of water vapor and laser is that the heating zone is generated inside the water vapor so that no heat load is applied to the combustion chamber or nozzle, so high temperature (high pressure) is generated without worrying about the heat resistance of the material. It can be done. By increasing the temperature, a large thrust can be produced with a low density propellant (with a small amount of propellant) (that is, Isp increases).

The laser power and water vapor flow rate can be controlled independently, but there is a limitation because if the water vapor flow rate is lowered too much to increase Isp, the water vapor becomes thinner and the laser absorption efficiency decreases. The propulsion efficiency η is the conversion efficiency from laser energy to fluid kinetic energy. Generally, when the propellant is heated with a low-intensity laser, low-temperature jetting results in low loss and energy conversion with high conversion efficiency occurs. On the other hand, when the temperature is raised to increase Isp, latent heat (evaporation heat and ionization energy) and radiation loss increase (proportional to the fourth power of temperature), and the conversion efficiency to kinetic energy decreases.

Incidentally, if the specific heat ratio is k, the gas constant per unit molecular weight of the propellant is R, and the heating temperature of the propellant by the laser is T, the specific thrust Isp obtained by laser heating is given by the equation (6). From formula (6), it is understood that the specific thrust can be controlled by the heating temperature.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a system block diagram showing an embodiment of the laser propulsion system of the present invention.

  The embodiment shown in FIG. 2 includes a power source 1 that supplies power to the system, a semiconductor power laser diode (LD) 2 that outputs a continuous laser, a semiconductor power laser pumped Q-switched YAG laser 3 that outputs a pulsed laser, The beam switch 4 switches between a continuous laser using a semiconductor power laser alone and a pulsed laser using a semiconductor power laser pumped Q-switch YAG laser, and a radiator 5 that cools the heat generated by the system.

The operation will be described with reference to FIG. The semiconductor power laser diode (LD) 2 is basically continuous oscillation and is suitable for generating a jet gas having a relatively low specific thrust. On the other hand, in order to obtain a high specific thrust, a pulse operation type laser device that generates a high peak pulse, for example, a semiconductor power laser excitation Q-switched YAG laser 3 is suitable. In this method, light generated by a semiconductor laser is used as an excitation source, and another solid-state laser is pulse-oscillated.

  The spacecraft laser propulsion system equipped with the laser system shown in Fig. 2 uses a pulse laser in the operation mode in which the spacecraft has a relatively small thrust but a high specific thrust with good fuel efficiency, that is, to increase the spacecraft propulsion speed. The semiconductor power laser excitation Q switch YAG laser 3 to be output is switched to be propelled.

On the other hand, if a large thrust is required to accelerate the spacecraft even if the fuel efficiency is somewhat poor, the semiconductor power laser diode (LD) 2 is switched to the single operation mode. The beam switch 4 performs switching control between a high specific thrust / low thrust mode and a low specific thrust / high output mode. The beam switch 4 switches between a continuous laser using a semiconductor power laser alone and a pulse laser using a semiconductor power laser pumped Q-switched YAG laser. Heat generated by the laser is cooled by the radiator 5.

As described above, for example, if the velocity of the ejected gas is increased, a large amount of momentum can be generated with a smaller amount of propellant. On the other hand, if the speed is reduced, the same momentum can be obtained with smaller energy. The former was a condition of electric propulsion (propulsion gas speed of 10km / s or more) such as "Falcon", and was able to fly to the asteroid with less propellant. The latter are HII-A rockets and jet engines (with a gas velocity of 5 km / s or less), and are used when chemical fuel can be used abundantly. In the laser propulsion system of the present invention, both of these performances can be realized by switching with a single engine system.

The Hayabusa spacecraft was equipped with four ion thrusters, but was navigating outer space with a thrust of 24 mN using three 8 mN ion thrusters simultaneously. The power supplied to the three ion thrusters is about 1 kW (power consumption of one ion thruster is 349 W), but it is equivalent to or higher by using the power installed in this spacecraft with a laser engine of a high power semiconductor laser alone or a semiconductor laser pumped YAG laser. Thrust can be generated.

This semiconductor laser excitation pulse YAG laser method is suitable for a fuel saving type with a high specific thrust, but a high thrust cannot be obtained accordingly. This is because the mass of ablated is small because only the surface of water is rapidly heated by a pulse laser having a high peak power in the Q switch method using a YAG laser. The fuel consumption is improved because the consumption of water as a propellant is reduced.

On the contrary, when high thrust is required even if the specific thrust is suppressed, a method of directly irradiating the propellant with a semiconductor laser is desirable. When the semiconductor laser is directly applied to water, heating occurs slowly, so that a large volume of water is simultaneously heated and the temperature is kept low as compared to the pulse, so that a large mass of low-temperature propellant is injected. Therefore, a large C _m is realized and a large thrust is obtained.

Therefore, two systems of semiconductor power laser that directly irradiates water as shown in FIG. 2 and semiconductor power laser pumped Q-switched YAG laser are prepared, high thrust low specific thrust mode (semiconductor power laser alone) and low thrust high It is desirable that the specific thrust mode (semiconductor power laser excitation Q-switched YAG laser) is arbitrarily switched to operate for orbiting the earth and flying in space.

FIG. 3 is a block diagram showing an example of the semiconductor power laser pumped Q-switched YAG laser shown in FIG.

In this method, light generated by a semiconductor laser is used as an excitation source, and another solid-state laser is pulse-oscillated. Referring to FIG. 3, a power source 1 for supplying power to the laser diode, a semiconductor power laser diode (LD) 2, a condensing lens 6 for condensing the laser beam, a laser medium 7, a Q switch element 8, And an output coupling mirror 9. In FIG. 3, components corresponding to those shown in FIG. 2 are denoted by the same reference numerals or symbols, and description thereof is omitted.

A solid-state laser can easily generate light pulses by using a crystal such as YAG that can store a large amount of energy as a laser medium and combining it with a Q switch element that stores light and emits it instantaneously.

FIG. 3 shows a typical power flow of system elements in the case of a power supply capacity of 1000 W as an example of output and efficiency. With this device, a system that generates a thrust of several millinewtons is possible. With a conversion efficiency of 70% for the semiconductor laser, an output of 700 W of laser power can be obtained from an output of 1000 W of the power supply 1. This is condensed by the condenser lens 6 and irradiated to the laser medium 7 (YAG rod). Considering the quantum efficiency of the laser medium 7, the power of 500 W excites the YAG rod of the laser medium 7.

The power output of the 250 W semiconductor laser pumped YAG laser is obtained through the output coupling mirror 9 with the conversion efficiency of the YAG laser being 50%. The power source has a rack shape size of about 30 cm square.

In order to absorb the laser in water, the wavelength of the laser is preferably in the 10.6 μm band of the CO2 laser. The wavelength of the YAG laser is 1.06 μm, but the YAG laser is used because it has a high energy density and can use a Q switch with a small device to generate a giant pulse. However, as described above, continuous output (CW), not pulse output, is suitable for water ablation for generating high thrust.

The YAG rod is generally excited by a flash lamp, but a high-power semiconductor laser is used. In addition, solar excitation has been studied. In the case of sunlight, since the spectrum is wide, the use of a rod in which the sensitizer Cr is mixed with Nd: YAG can correspond to a broad spectrum.

Since the wavelength of the LD semiconductor laser is a narrow band of 0.8-1μ band (narrow band), mixing ink with water (ink ink) to help water absorb the laser light will improve the absorption performance. is necessary. Power supply is required only for LD and cooling, and power supply to the YAG rod is not necessary.

FIG. 4 is a block diagram showing laser irradiation to heated steam.

Referring to FIG. 4, the nozzle 20, the steam preheating chamber 21, the nozzle wall surface 22, a laser window 23, a laser light source 24, a propellant tank 25, and a laser path 26 are configured.

A propellant is selected that has a low molecular weight, is easy to store, and has a relatively low temperature and high vapor pressure. Here, water is selected in consideration of chemical stability in addition to the conditions on the left. Steam 30 is generated in the steam preheating chamber 21 and guided to the nozzle 20. The water vapor 30 is injected from the nozzle wall surface 22 to fill the inside of the nozzle 20. The water vapor 30 is heated by the laser beam 31 irradiating the central portion of the nozzle 20 to become high temperature water vapor 32 and is ejected from the outlet of the nozzle 20. The laser light 31 is irradiated from the laser light source 24 to the water vapor 30 through the laser window 23 and the laser path 26.

The propulsion performance of the spacecraft is determined by the characteristics (velocity, temperature, density) of the water vapor 30 that is the jet gas and the diameter of the nozzle 20 (propulsion force by jet gas = density × (speed) ² , kinetic energy flow = density × ( speed) ^3/2 per both nozzle unit area). The thrust generated by the water vapor 30 which is the jet gas is transmitted to the nozzle wall surface 22 through the water vapor 30 in the nozzle 20 and becomes the thrust to the spacecraft. At this time, the vicinity of the surface of the nozzle wall surface 22 is in a low-temperature and high-density state, and the center (laser heating) portion of the nozzle 20 is in a high-temperature and low-density state, and the pressure distribution is kept uniform as a whole fluid. This is because if the flow is below the subsonic speed, the pressure wave generated by laser heating spreads throughout the fluid and the pressure becomes uniform. That is, the gas flow in the nozzle 20 is less than the speed of sound, and the reaction force that the water vapor 30 as the high-temperature gas is ejected from the nozzle 20 is efficiently transmitted to the nozzle wall surface 22 and becomes a thrust for driving the spacecraft.

Therefore, a rocket engine having a high specific thrust can be realized without being limited by the combustion chamber temperature and pressure.

Next, when high thrust is required, laser irradiation of water or ice in FIG. 5 is necessary.

FIG. 5 is an explanatory view showing laser irradiation to water.

Referring to FIG. 5, the nozzle 40, the water tank 41, water 42 or ice 43 stored in the nozzle 40, a laser system 44 and a light receiving plate 46 are configured. Most laser light is absorbed by the light receiving plate, where it is converted into thermal energy. An appropriate amount of water film covers the light receiving plate, and the heat energy is blown off and converted into kinetic energy. By setting the water film thickness appropriately, most of the thermal energy can be converted to kinetic energy, and a high energy efficiency (high Cm) propulsion can be obtained.

When ice 43 is present in the nozzle 40, laser light 45 is emitted from the laser system 44 and ice ablation occurs.

FIG. 6 is a schematic view showing a spacecraft on which the laser propulsion system shown in FIGS. 2, 3, 4, and 5 is mounted.

Referring to FIG. 6, the spacecraft 100 includes solar cell paddles 101 a and 101 b, a water tank and laser system 102, a nozzle 103, and a gimbal 104.

The water tank and laser system 102 and the nozzle 103 have the configurations shown in FIGS. 2, 3, 4, and 5, and a description thereof is omitted here.

The power of the spacecraft 100 is supplied from the two solar battery paddles 101a and 101b, and is mainly used as a primary power source for the system of the spacecraft 100. The generated electric power of the solar cell is generally about 0.13 kW / m ^{2. For} example, by mounting two 7 m × 5 m solar cell paddles, 9 kW of electric power can be obtained in the space near the earth.

Since the laser power supply power is not sufficient, a fuel cell (not shown) that is already installed in Gemini spacecraft, Apollo spacecraft, and space shuttle and has a track record of space use is applied to the laser power supply power. In particular, a polymer electrolyte fuel cell that can be expected to be small, light, low temperature, and generate a large amount of power and is currently used in a fuel cell vehicle is used as a primary power source. In 2007, a solid polymer fuel cell having a performance of 100 kW was mounted on an automobile. In the future, it is expected that 400 kW class polymer electrolyte fuel cells will appear from the early stage of development.

In addition, the spacecraft 100 is equipped with a lithium ion battery (not shown) as a secondary power source, charges the surplus power of the solar cell paddle and the fuel cell, and discharges and uses it when necessary.

Using either the output from the polymer electrolyte fuel cell or the output from the lithium-ion battery of the secondary power source, the semiconductor power for driving high thrust and low specific thrust is reduced as the semiconductor laser drive current source in FIG. Supplied to laser engines and semiconductor power laser pumped Q-switched YAG laser Q-switched YAG laser engine for propulsion of low thrust and high specific thrust. This power supply is partially used for cooling.

The propulsion mode engine to be used is selected by the switching control unit of the beam switch 4 in FIG.

The solar battery panel 101 of the spacecraft 100 is installed on the gimbal 104, and its attitude is controlled so that it always faces the sun. Moreover, the water produced | generated with a fuel cell can be reused not only as drinking water but as a propellant.
Table 1 shows an example of a draft specification of the spacecraft 100.

The semiconductor power laser is in a development state of high power year by year, and a several kW (several cm square) has been developed by the current stack array structure. A 100kW semiconductor power laser (10cm square) can be developed by the existing technology. However, semiconductor lasers have a larger beam spread than solid-state lasers and so on, so the spot size of the condensing point tends to be large, so the arrangement of the condensing lens and propellant can be designed in consideration of lens contamination. is necessary.

As an example of launching a spacecraft from the moon surface, in terms of calculation, if the efficiency is 0.8, the laser output is 8000 kW, and Isp = 350 seconds, the propulsive force F = 2 × 0.8 × 8000000 / (9.8 × 350) = 3.7 × 10 ³ N. Assuming that the mass of the spacecraft is m = 1000 kg, the acceleration α = 3.7 × 10 ³ /1000=3.7 m / s ² = 0.38G, the gravity of the moon is larger than 1 / 6G = 0.16G, and the space of 1 ton from the moon surface The machine will be launched.

Incidentally, an orbital speed of 1600 m / s at an altitude of 100 km can be obtained with an acceleration time of 460 seconds. This specific thrust Isp is controlled by the temperature T, but Isp 350 seconds is considerably low in laser ablation, which can be realized sufficiently. Since it becomes a low temperature propellant, the conversion efficiency is high and the propellant consumption is 50%.

Needless to say, the propellant is not limited to water, ice, and water vapor, and the propellant is a solid, liquid, or the like that is judged appropriate.

In addition, as described above, the laser propulsion system of the present invention is to operate by switching between continuous oscillation and pulse oscillation of the laser as a heating source of the propellant according to the performance required for the system, It goes without saying that solid lasers (crystal media, ceramic media, glass media), semiconductor lasers, fiber lasers, and the like can be combined in various ways according to the performance required for the system.

  The laser propulsion described in the present invention uses the reaction thrust of a water vapor explosion generated by irradiating water with laser light. Because it is water, laser ablation does not cause enormous air pollution and space environment pollution like aircraft and chemical rockets. Since water is used to replace fossil fuels such as gasoline as a propellant, CO2 emissions from aircraft are reduced, reducing the environmental impact of air transportation that will increase in the future, and instability due to environmental problems and fluctuations in crude oil prices. There is an advantage to lose.

Laser propulsion by steam explosion is not only aerospace use. It can be applied to non-exhaust gas laser piston engines that replace the gasoline of the current piston engine with water or seawater and ignite with a laser, so it can also be applied to cars and ships.

In the future, when the International Space Station ISS is in operation on the Earth orbit and a space hotel is built as a space tourism business, an inter-orbital transport such as movement between the space hotel and ISS or sightseeing to the moon will be required. Become. The full-scale joint development of the lunar base since 2015 will require transportation of goods and passengers, or a lunar vehicle that will fly on the lunar surface by inter-orbital transport instead of lunar vehicles. As such an interorbital transport aircraft and lunar vehicle, it is expected that laser propulsion devices using water or steam as fuel will be used in outer space like buses and cars.

1 Power supply 1
2 Semiconductor power laser diode (LD)
DESCRIPTION OF SYMBOLS 3 Semiconductor power laser excitation Q switch YAG laser 4 Beam switch 5 Radiator 6 Condensing lens 7 Laser medium 8 Q switch element 9 Output coupling mirror 20 Nozzle 21 Steam preheating chamber 22 Nozzle wall surface 23 Laser window 24 Laser light source 25 Propellant tank 26 Laser path 30 Water vapor 32 High temperature water vapor 40 Nozzle 41 Water tank 42 Water 43 Ice 44 Laser system 45 Laser light 100 Spacecraft 101a, 101b Solar cell paddle 102 Water tank and laser system 103 Nozzle 104 Gimbal

Claims (20)

A laser propulsion system that heats an arbitrary propellant with a laser and generates thrust using the kinetic energy of high-temperature and high-pressure steam generated. 2. The laser propulsion system according to claim 1, wherein the high-temperature and high-pressure steam directly absorbs laser energy and generates a thrust while suppressing a thermal load applied to the nozzle wall surface. The laser propulsion system according to claim 1 or 2, wherein the laser as a heating source of the propellant operates by arbitrarily switching between continuous oscillation and pulse oscillation. 4. The laser propulsion system according to claim 3, wherein the laser is a solid laser, a semiconductor laser, or a fiber laser used alone or in combination. A laser propulsion system comprising: a laser source that uses water as fuel and irradiates the water with laser light; and a power source that supplies power to the laser source. A laser propulsion system comprising water vapor that heats water, a laser source that irradiates the water vapor with laser light, and a power source that supplies power to the laser source. A laser propulsion system comprising a laser source having water and water vapor and irradiating one of them with a laser beam, and a power source for supplying power to the laser source. 8. The laser propulsion system according to claim 5, 6 or 7, wherein the laser source is a semiconductor laser. 8. The laser propulsion system according to claim 5, 6 or 7, wherein the laser source is a semiconductor laser excitation Q-switched solid state pulse laser. 8. The laser propulsion system according to claim 5, 6 or 7, wherein the laser source includes a semiconductor laser and a semiconductor laser excitation Q-switched solid-state pulse laser, and is switched to one of the laser sources. The laser propulsion system according to claim 9 or 10, wherein the solid-state laser is a YAG laser. The laser propulsion system according to any one of claims 5 to 11, wherein the power source is a fuel cell. The laser propulsion system according to claim 5, wherein the power source includes a fuel cell and a solar cell. The laser propulsion system according to claim 12 or 13, wherein the fuel cell is a polymer electrolyte fuel cell. A semiconductor laser, a beam changeover switch connected to the semiconductor laser, a Q-switch solid state pulse laser connected to the beam changeover switch, and a power supply for supplying power to the semiconductor laser, and propelled by the semiconductor laser by the beam changeover switch A laser propulsion system that switches between a first operation mode in which an agent is continuously irradiated and a second operation mode in which the propellant is pulse-irradiated by the Q-switched solid-state pulse laser based on excitation of the semiconductor laser. The laser propulsion system according to claim 15, wherein the propellant is water vapor, water, or ice. The laser propulsion system according to claim 15 or 16, wherein the solid-state laser is a YAG laser. The laser propulsion system according to claim 15, 16 or 17, wherein the power source includes one or both of a fuel cell and a solar cell. The laser propulsion system according to claim 18, wherein the fuel cell is a polymer electrolyte fuel cell. A spacecraft or aircraft equipped with the laser propulsion system according to any one of claims 1 to 19.