Solar-pumped laser power transmission, a way to dramatically decrease launch costs?
in [Physics]
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From: William Mook on 14 Feb 2010 14:24 On Feb 14, 1:33 pm, "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > "William Mook" <mokmedi...(a)gmail.com> wrote in message > > news:ec69fe16-04e1-4147-82e8-4f007cb68a41(a)g23g2000vbl.googlegroups.com... > On Feb 12, 5:16 pm, "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > > > > > "William Mook" <mokmedi...(a)gmail.com> wrote in message > > >news:fbbddf2d-60ea-4ed3-a183-23e920219728(a)k41g2000yqm.googlegroups.com.... > > On Dec 18 2009, 4:43 am, "Androcles" <Headmas...(a)Hogwarts.physics_q> > > wrote: > > > > "Jonathan" <H...(a)Again.net> wrote in message > > > >news:p5SdndXFAKoISrfWnZ2dnUVZ_vWdnZ2d(a)giganews.com... > > > > >I like this idea, Relatively small mirrors would power > > > > the lasers, not huge solar cell arrays. The lasers would > > > > transmit their beams to other satellites that convert it to, and > > > > beam it down, as microwaves. No need for mile-size > > > > collectors in orbit. > > > > What are you babbling about? > > > I can't be certain, but I will say that if you move a solar collector > > array closer to the sun it will gather more energy for a given size. > > ============================================= > > It won't be in Earth orbit then. > > That is absolutely correct.  It will be on solar orbit.  The orbital > period will be 24 hours at 3 million km radius. > ============================================== > You may find it a tad warm 2 million miles from the sun. It will gather > rather more energy than you wanted, and having a 24-hour year it won't >  be in sight of Earth for more than 14 hours each Earth day as it > disappears behind the Sun for 10 hours of that period. The sun is 1.4 million km in diameter. An orbit with a 3 million km radius has a 6 million km diameter. So, the sun subtends only 13.5 degrees of the sky. This means that if you are dumb enough to place the satellite in precisely the same orbital plane as the Earth orbits, it will not be visible 54 minutes out of every 24 hours because the Earth will be behind the sun from the viewpoint of the satellite. Now, the Earth is 150 million km removed from the sun. By tilting the orbital plane of the closely orbiting satellite by 7 degrees it will be visible from Earth even on the opposite side of the sun. The same technique of solar sailing that brought the satellite from Earth, is used to maintain a 1 degree per day precession of its orbit so that the Earth is visible throughout the year 24/7 from this orbit. Regarding heat. Multi-spectral solar cells are 65% efficient. Free electron lasers are 85% efficient. So, at the satellites 55.25% of the energy leaves as laser light. 44.75% of the energy must leave by radiant heat or reflected away at the outset. This is the heat balance that drives the temperature. Each square meter of area normal to the incident radiation receives energy. Twice this area is the radiating area for a large surface. Stephan Boltzman gives us the temperature needed. Alright, at 3 million km from the sun, 3.45 MW is intercepted by each square meter. 690 kW is reflected away as ineffective light. 1,906 kW is beamed away as laser energy. This leaves 854 kW to be radiated away by satellite heating over 2 square meters. That's 427 kW per square meter. Stephan -Boltzman says temperature and heat flux for a radiant source are related by j* = sigma * T^4 So, T = (j* / sigma) ^(1/4) = (427,000 / 5.67e-8)^(1/4) = 1,656.6K This is 1,383.7 celsius or 2,522.6 fahrenheit This is below the melting point of Silicon, which is why I selected this distances. Of course, the challenge will be to build something that operates at these temperatures. Here is the list of elements we have to work with; We should be able to do something interesting with these 33 elements. No. Name____ Sym Melting Point 66 Dysprosium____ Dy 1,407 °C (1,680 K) 14 Silicon_______ Si 1,410 °C (1,680 K) 28 Nickel________ Ni 1,453 °C (1,726 K) 67 Holmium______ Ho 1,470 °C (1,740 K) 27 Cobalt________ Co 1,495 °C (1,768 K) 68 Erbium_______ Er 1,522 °C (1,795 K) 39 Yttrium_______ Y 1,526 °C (1,799 K) 26 Iron__________ Fe 1,535 °C (1,808 K) 21 Scandium_____ Sc 1,539 °C (1,812 K) 69 Thulium_______ Tm 1,545 °C (1,818 K) 46 Palladium_____ Pd 1,552 °C (1,825 K) 91 Protactinium___ Pa 1,600 °C (1,870 K) 98 Californium____ Cf 1,652 °C (1,925 K) 22 Titanium______ Ti 1,660 °C (1,930 K) 71 Lutetium______ Lu 1,663 °C (1,936 K) 90 Thorium______ Th 1,755 °C (2,028 K) 78 Platinum______ Pt 1,772 °C (2,045 K) 40 Zirconium_____ Zr 1,852 °C (2,125 K) 24 Chromium_____ Cr 1,857 °C (2,130 K) 23 Vanadium_____ V 1,902 °C (2,175 K) 45 Rhodium______ Rh 1,966 °C (2,239 K) 43 Technetium____ Tc 2,200 °C (2,470 K) 72 Hafnium_______ Hf 2,227 °C (2,500 K) 44 Ruthenium_____ Ru 2,250 °C (2,520 K) 5 Boron_________ B 2,300 °C (2,570 K) 77 Iridium________ Ir 2,443 °C (2,716 K) 41 Niobium_______ Nb 2,468 °C (2,741 K) 42 Molybdenum__ Mo 2,617 °C (2,890 K) 73 Tantalum______ Ta 2,996 °C (3,269 K) 76 Osmium_______ Os 150 3,027 °C (3,300 K) 75 Rhenium______ Re 3,180 °C (3,450 K) 74 Tungsten______ W 3,422 °C (3,695 K) 6 Carbon (diamond) C 3,550 °C (3,820 K) 6 Carbon (graphite) C 3,675 °C (3,948 K) As we recede from the sun a similar calculation can be obtained At 10 million km the temperature drops to 907.8 K (1,174.3 F, 634.6 C) and the list enlarges. Energy density drops to 311.1 kW per square meter , reflected energy 62.2 kW per square meter, beamed energy 171.9 kW per square meter and half the remainder is radiated away. At 30 million km the temperature drops to 497.5 K (224.4 C, 435.8 F) and we enter the realm of today's solid state devices. Energy drops to 28.1 kW per square meter and reflected energy is 5.6 kW while laser energy is 15.5 kW per square meter - and heat is half the remaining flux. Of course, active cooling of sections, that use radiator temps higher than these is also possible - and quite likely - given the power levels and temperatures. MEMS based refrigeration - powered by the copius energy available - is well worth the effort. http://www.patentstorm.us/patents/7263838.html That is, say 10% of the total energy is needed to operate a refrigerator that lets you operate 1/2 the distance otherwise. This increases your power level by 4x and gives you a 3.6x advantage!
From: William Mook on 14 Feb 2010 14:58 On Feb 14, 2:00 pm, "Scott M. Kozel" <koze...(a)comcast.net> wrote: > "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > > > "William Mook" <mokmedi...(a)gmail.com> wrote in message > > > That is absolutely correct. It will be on solar orbit. The orbital > > period will be 24 hours at 3 million km radius. > > ============================================== > > You may find it a tad warm 2 million miles from the sun. It will gather > > rather more energy than you wanted, and having a 24-hour year it won't > > be in sight of Earth for more than 14 hours each Earth day as it > > disappears behind the Sun for 10 hours of that period. > > It would take an enormous amount of energy to put a satellite that far > down into the Sun's gravity well. > > It has been difficult enough to get a satellite into the same orbit as > Mercury, which is 35 million miles from the Sun. Solar sails are ideally suited for this mission. I am considering fully reusable vehicles capable of putting 1,000 metric ton payloads on orbit for very little cost per ton. This sort of vehicle is required to build any sort of orbital or lunar or Martian infrastructure. Its well within our capacity to build it. http://www.scribd.com/doc/24390383/mokaerospace-3 There are 10 million millionaires in the world and they control $40 trillion of the world's $58 trillion in liquid wealth. Selling 5,000 tickets to 0.05% of them for $200,000 raises $10 billion - enough to build a fleet of ships. Once built, reusable vehicles are useful for a variety of missions. There are two sorts of orbits. One involves a slow spiral outward from Earth then inward into the desired orbit using solar light pressure acting on a satellite orbited to GEO. That satellite uses solar sails to maintain the orbit so that it is always visible from Earth as I've described elsewhere. The other involves using a gravity boost at Jupiter to cancel all orbital motion, and then using light pressure to hold the satellite at the desired altitude. Using light pressure to maintain relative position with Earth. This limits the mass density of the power sat, but that is a goal of light sail technology anyway. Stationary powersats hovering above the solar surface by light pressure (ideally using the ineffective photons not needed to operate the equipment) are not only useful for powering planets, like the Earth, but also useful powering interstellar transport and interplanetary transport, since the satellite can navigate to always be between the target and the sun. Reflecting 20% of the photons at 3 million km from the sun produces a pressure of 4.6 pascals away from the sun. Thus, 469 grams per square meter is possible to have at this distance. The solar sail and controls and so forth will mass 58.5 grams per square meter. This leaves 410 grams per square meter operating mass. With something like silicon is means we can plate the sail with 400 microns of solid silicon material. Thicker using diamond, and thicker still using structured carbon and silicon. Trying out the satellite design on a smaller scale makes sense before building a large system. A 10 metric ton payload sent to LEO - would cover 21,322 square meters. It would produce a laser beam 73 GW and be 164.7 m in diameter and produce a beam at Earth of comparable size if wavelength is chosen correctly. A similar satellite in GEO would intercept the laser energy and direct it to users anywhere in cislunar space. A 1,000 metric ton payload covers 100x the area, is 10x the diameter, and produces 7.3 TW - about 1/3 of what the world needs. A half a dozen launches of the larger satellite resolves our energy problems and earns trillions of dollars for the owners each year, while unleashing our economy from the constraints and problems of oil. Reflecting nearly all the energy during transit - except for shipboard power during transit - would allow light thrust 5x that in normal operation during transit. A thin layer of reflective materials - GBO film or aluminized films - would be discarded once final orbit was achieved in this case. Blow away a thin reflective layer by switching on the laser beam - and doing so in such a way as to fix the final orbital parameters - using the blown away film as propellant. It would take only a few months for these satellites once launched into LEO to make their way to their final destination and begin operations.
From: William Mook on 14 Feb 2010 14:59 On Feb 14, 2:12 pm, David Spain <nos...(a)127.0.0.1> wrote: > William Mook <mokmedi...(a)gmail.com> writes: > > Silicon receivers collect the 1,100 nm photons and convert them with > > over 90% efficiency to electricity. > > > Sun --> Electrons ---> Laser ---> Electrons > > Low 60% 80% 90% overall 43.2% > > High 65% 85% 95% overall 52.4% > > Do you have or know of any working lab examples of Laser->Electron conversion > efficiencies of 90+%? Cites or references appreciated. > > Isn't there a problem with surface area illumination of the cells with a tight > beam or is the beam dispersion high enough to give a higher surface area > illumination? > > How does your proposed Laser illumination compare to solar illumination in terms > of multiples of suns? > > >Just as phased array techniques may be used to direct multiple > >microwave beams anywhere reliably, so too can holographic techniques > >be used to direct multiple laser beams anywhere reliably. I have even > >pioneered a technique to use 4-wave mixing to allow satellites or > >other emitters connect to any number of users at the same time > > >http://www.youtube.com/watch?v=2QAUkt2VPHI > > This video was marked private and I couldn't view it. > > Dave really? I'll check into that.
From: William Mook on 14 Feb 2010 15:15 On Feb 14, 2:12 pm, David Spain <nos...(a)127.0.0.1> wrote: > William Mook <mokmedi...(a)gmail.com> writes: > > Silicon receivers collect the 1,100 nm photons and convert them with > > over 90% efficiency to electricity. > > > Sun --> Electrons ---> Laser ---> Electrons > > Low 60% 80% 90% overall 43.2% > > High 65% 85% 95% overall 52.4% > > Do you have or know of any working lab examples of Laser->Electron conversion > efficiencies of 90+%? Cites or references appreciated. E. F. Zalewski and J. Geist, "Silicon photodiode absolute spectral response self-calibration," Appl. Opt. 19, 1214-1216 (1980) http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-19-8-1214 > Isn't there a problem with surface area illumination of the cells with a tight > beam or is the beam dispersion high enough to give a higher surface area > illumination? The laser emitter surface is an engineered surface. In a solid state implementation you have a number of wigglers operating in parallel across a surface - in phase - in a way that takes the light created and expands their area to fill the surface - while controlling their phase in a way that allows well defined beams from that area to be formed. > How does your proposed Laser illumination compare to solar illumination in terms > of multiples of suns? Well, I have designed systems that operate at GEO - collecting sunlight at 1,380 W/m2 - and beam energy down to Earth at 680 W/m2 - in the 1,100 nm band. So you can see diode brightness is not a problem. This is the same energy density of sunlight in the IR - and 1,100 nm is pretty free of dispersion (if there are no clouds) Which is true in most locations where solar panels would be operating commercially (that's how the ground stations get built) So, the environmental impact is doable for testing - and we adjust from there based on data. Later systems I hope to operate at 20 W/cm2 - once the beam steering is proven - and this is suitable for mobile applications as well - forming beams as small as 10 cm across - 1,570 Watts - which is sufficient for home use - this for terrestrial applications. Systems that beam energy from near the sun to GEO operate at a native 200 W/cm2 point to point - and are 200 m across and more - 60 GW+ links - for powering larger industrial applications off world - and for propulsive systems. Higher intensities are used along with larger areas for terawatt scale interstellar laser light sail operations. > >Just as phased array techniques may be used to direct multiple > >microwave beams anywhere reliably, so too can holographic techniques > >be used to direct multiple laser beams anywhere reliably. I have even > >pioneered a technique to use 4-wave mixing to allow satellites or > >other emitters connect to any number of users at the same time > > >http://www.youtube.com/watch?v=2QAUkt2VPHI > > This video was marked private and I couldn't view it. > > Dave It was marked private. I don't know how that happened. I've marked it public again.
From: William Mook on 14 Feb 2010 15:16
On Feb 14, 2:56 pm, Fred J. McCall <fjmcc...(a)gmail.com> wrote: > William Mook <mokmedi...(a)gmail.com> wrote: > > :On Feb 13, 2:48 am, "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > :> "Pat Flannery" <flan...(a)daktel.com> wrote > :> > :> > I can't be certain, but I will say that if you move a solar collector > :> > array closer to the sun it will gather more energy for a given size. > :> > :> You should be certain before you give us your stupid opinion, Pat Flannery. > : > :My opinions are not stupid. > : > > BWAAAAAHAAAAHahahahahahahahahahhahhaahhaaa!!!!!!!! > > -- > "Ordinarily he is insane. But he has lucid moments when he is > only stupid." > -- Heinrich Heine Off your medication again I see. |