eder@ssc-vax.UUCP (Dani Eder) (05/30/87)
In article <5893@brl-smoke.ARPA>, gwyn@brl-smoke.ARPA (Doug Gwyn ) writes: > In article <1115@oliveb.UUCP> gnome@oliveb.UUCP (Gary) writes: > -Well, according to the May 7 MACHINE DESIGN, Lockheed-Georgia has entered > -a proposal to create a smaller version of "Project Flashlight". > -Their idea is to beam 2MW of power (as microwaves) at their unmanned planes > -in order to keep them in a figure-8 watchdog position over an area for > -60 to 90 days. > > I really think this (as well as similar ideas for beaming power > to Earth from solar-collector satellites) is extremely dangerous. > What is to keep someone (even a poor little bird) from flying > through the beam by accident? I was part of a study in 1984 that looked at design of a Solar Power Satellite made from lunar materials (the report is published as volume 6 #1 of the journal 'Space Power', 1986). The direct answer to your question is 'nothing'. At least in the space-based power supply scenario we looked at, the maximum beam intensity was required to be no more than 300 watts per square meter. This is 30% of peak desert noonday sunlight intensity. Unless the receiving antenna were located in a desert area, the combined sunlight+microwave intensity will be well within tolerable limits for humans and animals. Now, an SPS will not likely be located in a desert, since you generally want to get power to where people are. As for airplanes, the beam area will probably be marked as a keep out zone, to prevent long-term low level exposure to passengers and crew. Of course, an airplane could stray into the beam by accident, but the metal skin of the plane will reduce the interior intensity to only a few watts per square meter, and the plane will generally be through the beam in less than a minute. As for someone wandering into the beam on the ground, they would have to climb two fences, then hike about two miles to the center of the beam. Then they would have to climb up on the receiving antennas to get the full beam intensity. Standing underneath doesn't get you much. So, it is physically possible, but it makes about as much sense as intentionally walking into the firebox of a coal-fired power plant. As for the beam itself wandering, the beam is produced by a phased array of microwave transmitters in space. The control signal is coming from a transmitter located in the center of the receiving antenna on the ground, and is powered by the incoming beam. So, if the beam wanders, the control signal turns off, and the phased array loses phase lock, spreading its' beam over the entire earth, where it becomes a harmless intensity (less than TV intensity in most areas). I do not know of the microwave powered airplane design rules, so I cannot comment on it's safety. If there is anything more you would like to know about Solar Power Satellites, let me know. Dani Eder/Advanced Space Transportation/Boeing/ssc-vax!eder
ems@apple.UUCP (Mike Smith) (06/01/87)
In article <1266@ssc-vax.UUCP>, eder@ssc-vax.UUCP (Dani Eder) writes: > In article <5893@brl-smoke.ARPA>, gwyn@brl-smoke.ARPA (Doug Gwyn ) writes: > > In article <1115@oliveb.UUCP> gnome@oliveb.UUCP (Gary) writes: > > ... > > What is to keep someone (even a poor little bird) from flying > > through the beam by accident? > > [...] The direct answer to your question is 'nothing'. [...] Not quite nothing, but very close to it. Birds have been shown to stop flying and WALK through an area of high microwave flux near radar antennas. I would expect many birds to get 'nuked' into confusion. > [...] As for airplanes, the beam area > will probably be marked as a keep out zone, to prevent long-term low > level exposure to passengers and crew. Of course, an airplane could > stray into the beam by accident, but the metal skin of the plane will > reduce the interior intensity to only a few watts per square meter, and > the plane will generally be through the beam in less than a minute. Can you say 'Fiberglass'? There, I knew you could! And now try Kevlar, boron composite, and Plexiglass. If you think it is only a few high tech craft that have this problem, try Wood and Cloth. I fly a glider. It is metal tubing covered with cloth and paint. There is a plexiglass bubble above me. Gliders tend to do lazy circles in thermals and hang around an area for a long time. They also wander cross country based on the wind and lift. Please paint the power recieving station in a skull and cross bones pattern with black and red paint. And don't try to radio me, many gliders don't have radios or an electical system... -- E. Michael Smith ...!sun!apple!ems 'If you can dream it, you can do it' Walt Disney This is the obligatory disclaimer of everything. (Including but not limited to: typos, spelling, diction, logic, and nuclear war)
gwyn@brl-smoke.ARPA (Doug Gwyn ) (06/02/87)
In article <1266@ssc-vax.UUCP> eder@ssc-vax.UUCP (Dani Eder) writes: >... At least in the space-based power >supply scenario we looked at, the maximum beam intensity was required >to be no more than 300 watts per square meter. This is 30% of peak >desert noonday sunlight intensity. ... Assuming all that's correct, is 300W/m^2 a safe dosage for microwaves? They have considerably different frequency than sunlight, so the body's response to them would be via different mechanisms. In particular I suspect that might be enough to cause corneal damage within a short amount of time. Could somebody with microwave safety information check this?
ornitz@kodak.UUCP (06/02/87)
In article <5934@brl-smoke.ARPA> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes: >In article <1266@ssc-vax.UUCP> eder@ssc-vax.UUCP (Dani Eder) writes: >>... At least in the space-based power >>supply scenario we looked at, the maximum beam intensity was required >>to be no more than 300 watts per square meter. This is 30% of peak >>desert noonday sunlight intensity. ... > >Assuming all that's correct, is 300W/m^2 a safe dosage for microwaves? >They have considerably different frequency than sunlight, so the body's >response to them would be via different mechanisms. In particular I >suspect that might be enough to cause corneal damage within a short >amount of time. > >Could somebody with microwave safety information check this? The current ANSI standard for microwave exposure is 5 milliwatts per square centimeter in the frequency range of 1.5 to 100 GHz. This works out to 50 watts per square meter which is less than the 300 w/m**2 listed for sunlight. For frequencies in the range of 300 to 1500 MHz, the maximum power density for human exposure is f/300 mW/cm**2 where f is the frequency in megaHertz. These limits may be exceeded if the exposure conditions can be shown by laboratory procedures to produce specific absorption rates of less than 0.4 W/kg averaged over the whole body and spatial peak values below 8 W/kg over any one gram of tissue. These values are all time averaged over a six minute period. Consult ANSI Standard C95.1-1982 for more details. You are correct about cornea damage; because the cornea cannot dissipate heat like the rest of the body, it is the most sensitive organ to microwave energy. Barry ----------------- | ___ ________ | | | / / | | Dr. Barry L. Ornitz UUCP:...!rochester!kodak!ornitz | | / / | | Eastman Kodak Company | |< < K O D A K| | Eastman Chemicals Division Research Laboratories | | \ \ | | P. O. Box 1972 | |__\ \________| | Kingsport, TN 37662 615/229-4904 -----------------
jnp@calmasd.GE.COM (John Pantone) (06/02/87)
In article <892@apple.UUCP>, ems@apple.UUCP (Mike Smith) writes: ...microwave power transmission discussion... > I fly a glider. It is metal tubing covered with cloth and paint. There > is a plexiglass bubble above me. Gliders tend to do lazy circles in > thermals and hang around an area for a long time. They also wander > cross country based on the wind and lift. Please paint the power > recieving station in a skull and cross bones pattern with black and red > paint. And don't try to radio me, many gliders don't have radios or an > electical system... Do they also tend to be ignorant of restricted areas? Do they wander across country without sectionals - or any regard for others? If you fly anything - glider - 747 - F14 - you have the responsibility for staying out of restricted areas. No need to wory about the microwave receiver area - it will be marked well on all sectionals. -- These opinions are solely mine and in no way reflect those of my employer. John M. Pantone @ GE/Calma R&D, Data Management Group, San Diego ...{ucbvax|decvax}!sdcsvax!calmasd!jnp jnp@calmasd.Gseparr
jim@oswald.UUCP (06/03/87)
In article <892@apple.UUCP> ems@apple.UUCP (Mike Smith) writes: >I fly a glider. It is metal tubing covered with cloth and paint. There is >a plexiglass bubble above me ... Please paint the power receiving station >in a skull and cross bones pattern with black and red paint. And don't >try to radio me, many gliders don't have radios or an electical system... But hopefully they do carry aeronautical charts which depict the various Restricted Areas and Prohibited Areas. Encroaching on these areas is illegal and dangerous (you stand a significant risk of being shot at). There are many such areas now; a power receiving station would just be one more. -- Jim Olsen ...!{decvax,lll-crg,mit-eddie,seismo}!ll-xn!oswald!jim
mac@uvacs.UUCP (06/03/87)
It strikes me that the great potential of a solar microwavepower station is as a weapon. Properly refocused, of course. I can see why other countries might be leery of having us orbit one. And vice versa.
eder@ssc-vax.UUCP (06/04/87)
In article <892@apple.UUCP>, ems@apple.UUCP (Mike Smith) writes: > In article <1266@ssc-vax.UUCP>, eder@ssc-vax.UUCP (Dani Eder) writes: > > [...] As for airplanes, the beam area > > will probably be marked as a keep out zone, to prevent long-term low > > level exposure to passengers and crew. Of course, an airplane could > > stray into the beam by accident, but the metal skin of the plane will > > reduce the interior intensity to only a few watts per square meter, and > > the plane will generally be through the beam in less than a minute. > > I fly a glider. It is metal tubing covered with cloth and paint. There > is a plexiglass bubble above me. Gliders tend to do lazy circles in > thermals and hang around an area for a long time. They also wander > cross country based on the wind and lift. Please paint the power > recieving station in a skull and cross bones pattern with black and red > paint. And don't try to radio me, many gliders don't have radios or an > electical system... > E. Michael Smith ...!sun!apple!ems Do you fly into controlled airspace? Restricted areas (as in military practice areas)? I assume even glider pilots have to follow the rules of the air as to where they are allowed to fly. For safety, the air above a rectenna will most likely be designated some kind of restricted airspace, and it is the responsibility of the pilot to stay out of the way, just as ultralights are not allowed into the approach paths leading to big airports. In my earlier posting, I was referring to commercial airliners, who will have a conductive skin even if the main structure is non-metallic. This is for lightning strike protection, and so that traffic control radars can find them. Dani Eder/Boeing/Advanced Space Transportation/ssc-vax!eder
eder@ssc-vax.UUCP (Dani Eder) (06/06/87)
In article <1541@uvacs.CS.VIRGINIA.EDU>, mac@uvacs.CS.VIRGINIA.EDU (Alex Colvin) writes: > It strikes me that the great potential of a solar microwavepower station is > as a weapon. Properly refocused, of course. > I can see why other countries might be leery of having us orbit one. > And vice versa. The problem is how to focus thmicrowaves. In the canonical SPS design, the microwave wavelength is 12 centimeters (2.45 GigaHertz) because (a) it is efficiently transmitted through the atmosphere, and (b) electric to microwave conversion can be done with high efficiency at this wavelength. At higher frequencies (shorter wavelengths), both of these conditions get worse. Now, the resolving power of any optical element is approximately lambda/D, where lambda is the wavelength and D is the diameter of the element. In the case of the SPS, the microwave transmitter is about 1.2 kilometers in diameter. Thus lambda/D=0.0001 radians. At the 19000 km altitude of a synchronous satellite, the minimum spot size on the ground is then 1.9 km in diameter, which makes for a lousy weapon. If you want to make a weapon of an SPS, you want to go to a much shorter wavelength. Light, for instance. Our electric-to-visible light converters are presently of low efficiency, but there is much money being spent on improving them (free electron lasers for SDI). here the wavelength would be 500 nanometers (yellow), and the aperture diameter would be, say 10 meters. Then lambda/D would be 5x10E-8, giving a minimum spot size of 1 meter. This is much more useful as a weapon. Dani Eder/Boeing/Advanced Space Transportation/ssc-vax!eder
gdelong@cvbnet.UUCP (Gary Delong) (07/06/87)
In article <868@kodak.UUCP>, ornitz@kodak.UUCP (barry ornitz) writes: > > The current ANSI standard for microwave exposure is 5 milliwatts per square > centimeter in the frequency range of 1.5 to 100 GHz. This works out to 50 > watts per square meter which is less than the 300 w/m**2 listed for sunlight. > For frequencies in the range of 300 to 1500 MHz, the maximum power density > for human exposure is f/300 mW/cm**2 where f is the frequency in megaHertz. Barry, your posting got me to wondering about some other aspect of microwave hazard which has been an infrequent subject of conversation with some of my friends who drive cars with funny lights on top. You posting to me indicated you were knowledgeable in this field so I would like to know what you feel the risk is to police officers with X-band radar units mounted on the inside or outside of a rear side window pointed forward. I have always felt that the operator was in risk with this placement, but have not seen any reports either pro or con. Comments...? -- _____ / \ / All spelling errors | Gary A. Delong, N1BIP | \ / intentional for testing | linus!raybed2!cvbnet!gdelong \____\/ rn spellcorrector v1.02A. | (617) 275-1800 x5232