SPACE STUDIES INSTITUTE
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PRINCETON, NEW JERSEY 08542
[[librarian note: This address is here, as it was in the original printed newsletter, for historical reasons. It is no longer the physical address of SSI. For contributions, please see this page]]
THE HIGH FRONTIER® NEWSLETTER
VOLUME XX ISSUE 5 SEPTEMBER/OCTOBER 1994
DYSON TO RECEIVE FERMI AWARD
SSI is pleased to announce that Professor Freean J. Dyson, SSI president and professor emeritus at the Institute for Advanced Study, has been selected to receive the Enrico Fermi Award. The award is given for lifelong achievement in nuclear science.
The Fermi Award is the nation’s oldest science and technology award, and is administered by the Department of Energy for the White House. It will be presented at a ceremony in Washington at a date to be announced.
Dyson will receive the award from President Clinton “for his contributions to fundamental scientific knowledge in fields as diverse as physics, biology, astronomy and mathematics; for his courageous questioning of the risks and benefits of science and technology, and for his wonderful articles and books that describe to the public how a scientist looks at the world.”
Professor Dyson was born in Berkshire, England, and earned his BA. in mathematics at the University of Cambridge. His graduate studies were at Trinity College, Cambridge and Cornell University. He has been at the Institute for Advanced Study since 1973 and president of SSI since 1992.
FROM SSI HEADQUARTERS
SSI Conference May 4-7, 1995
Details of the SSI Conference XXII appear on page 5 of this newsletter. If you are interested in presenting a paper, poster, or participating as an observer and want additional information, please complete the card included with this issue and return it to our office.
A special program note: Dr. Brown will give a demonstration of his research, which is featured in this issue, on May 4. In the demonstration, microwave power will be beamed a distance of forty feet and converted back to DC power to energize a bank of lights.
SSI is in need of a Macintosh computer with a superdrive which allows you to read PC disks. We are told these are standard in computers past the Macintosh IIx. We generally use IBM-compatible computers, but this particular computer is needed to communicate electronically. If you are interested in donating your computer, please contact our office and speak to either Barbara or Jay. Remember, all donations are tax-exempt.
Astronomy magazine has offered a free issue and discount subscriptions to SSI members. If you are interested in either of these offers, please complete the enclosed offer form and return it directly to Astronomy. In addition to these offers, Astronomy will be making complimentary copies of the magazine available at the May conference.
Avis Car Rental
Avis rental car agency is offering a 10% discount off their super-saver rate and 5% off promotional prices to all SSI members using their agency. To take advantage of this offer, mention that you are an SSI member under the group code: T070000 when making your reservation. You will receive a discount, and SSI will receive a percentage of your rental charge.
TERRESTRIAL SIMULATION AND DEMONSTRATION OF THE SPS TRANSMITTER
By William C. Brown
Microwave Power Transmission Systems
The Space Studies Institute is currently supporting a demonstration program on beamed microwave power transmission with MPT Systems and the University of Alaska. The first milestone of the program was a horizontal demonstration of beamed power transmission that used components in the transmitter that closely simulated the components that would be used in the transmitter of the SPS. That demonstration was recently successfully carried out before the attendees of the 29th Symposium of the International Microwave Power Institute in Chicago on July 26. IMPI, the International Microwave Power Institute, is a professional organization that is devoted to the commercial applications of microwave power that includes the microwave oven and large-scale industrial microwave processing of many different materials. The demonstration was part of a special program on beamed power transmission that had been arranged for IMPI by Dr. Peter Glaser.
A special feature of the demonstration was its portability. The combined weight of the microwave transmitter that beamed the power and the rectenna that received the power and converted it back into DC power was 30 pounds. The demonstration was packed for transportation in a wooden box containing 9 cubic feet of volume. The rectenna and the transmitting module are set up on tripods as shown in Figure 1. The tripod mounting allows easy and accurate pointing of the microwave beam.
The similarity of the transmitter module used in the demo to those used in the Solar Power Satellite may be seen by comparing the antenna in Figure 1 with the artists concept of the transmitter in the Solar Power Satellite shown in Figure 2, and with the array of transmitting modules shown in Figure 3.1
The transmitting module in the SPS consists of a section of slotted waveguide antenna which is supplied with power from a magnetron that is combined with external circuitry to produce a high-gain, phase-locked amplifier. The magnetron in space is designed with a pyrolytic graphite radiator to radiate into heat caused by inefficiencies directly into space. The terrestrial simulation of the transmitting module is a section of slotted waveguide antenna which is supplied with power from a conventional microwave oven magnetron which also has been combined with external circuitry to produce a high-grain, phase-lock amplifier. A very interesting aspect of the Earth-based simulation of the SPS module is that it can be used directly in electronically steerable arrays for beaming power to high altitude microwave-powered aircraft such as the airship shown in Figure 4.2 In that sense, the module and the application in which it is used, is also part of the terracing approach to the SPS as advocated by Dr. Glaser.
An electronically steerable phased array, whether it be for the SPS or for a microwavepowered aircraft application is necessarily composed of transmitting modules such as shown in Figure 4. The key feature of these modules is that the phase of their microwave radiated output can be changed relative to that of other modules to change the pointing direction of the beam as a whole.
The two key features of the steerablephased array module, which has been given the acronym SPAM, is the slotted waveguide array and the microwave source which is the magnetron directional amplifier, or MDA. These two features will now be discussed.
The Slotted Waveguide Array
It was concluded early in the DOE/NASA-sponsored study of the SPS that the transmitting antenna should be a slotted waveguide array because of its 100% radiation efficiency as contrasted to any other approach. The problem then arose as to a method of making such arrays in space. The response to this challenge was the fabrication method shown in Figure 5. In this fabrication method, rolls of very thin aluminum material may be sent to orbit and formed into the sections of slotted waveguide array by a folding and welding process.3 The array shown in Figure 1 was formed by the process shown in Figure 5, but with simple tooling as contrasted to the tooling needed for large-scale production. The terrestrial economic payoff in this approach that was inspired and motivated by the SPS concept is very large. Basically, the major cost is the material itself, and this is 20 mm thick aluminum rolled stock, representing a material cost of about $2 per square foot of the array. In space the material thickness would be 5 mm.
The Magnetron Directional Amplifier or MDA
A requirement placed upon the amplifier in a steerable-phased array is that the phase of the output must always be some integral multiple of 360 electrical degrees regardless of the operating conditions imposed upon the amplifier. But how do you convert a magnetron which is a one-terminal device operating as a free-running oscillator into a phase-locked, high-gain, two-terminal amplifier? The answer is that the conversion is accomplished with external circuitry that involves the use of a ferrite circulator so that the magnetron itself does not need to be modified. But this two-terminal device which has been created has unique properties which obey an equation derived by Edward David, which I first came across in Volume 2 of Crossed Field Microwave Devices, edited by Ernest Okress and published by Academic Press, in 1961.4 The equation1 which indicates the phase shift between input and output as a function of several parameters follows:
where ∅ = phase shift between input and output of amplifier
f = free-running frequency of the magnetron
fo = frequency of the drive source
Pi = power input from the driver
Po = power out of the directional amplifier
ΩE = External Ω of the magnetron.
In this equation, the free-running frequency of the magnetron is defined as the frequency of operation of the MDA if the drive signal is removed.
It is clear that if the phase shift between input and output is to remain near zero, then the expression on the right-hand side of the equation must remain near zero also. This means that the frequency difference between the free-running frequency, f, of the magnetron and the frequency of the drive signal, fo, must be near zero. Because the free-running frequency of the magnetron can change greatly and rapidly with a change in its operating environment, it is not practical to set f equal to fo and expect the phase shift to remain near zero. But would it be possible to use the phase deviation caused by a drift in the value of f-fo to retune the magnetron in a simple negative feedback loop? It is indeed possible, and it is surprising that this was not done until the author became interested in doing so in the early 1980s.
It will be noted that if the term f-fo can be held close to zero by the feedback loop, the term in the denominator that defines the ratio of the power of the drive signal to the output power can be decreased to low values corresponding to power gains of 1000 (30 db) or more. The magnetron directional amplifier in the demonstration operated with a power gain of 10000 or 30 db, with a phase error of only 2 or 3 degrees. Depending upon the amount of phase error that can be tolerated, the gain could be raised to 40 db.
The tuning of the free-running frequency of the magnetron, f, in the feedback loop can be accomplished either by altering the internal resonant frequency of the device by means of a mechanical tuner or by taking advantage of two ways in which the frequency can be varied by external means. Altering the internal resonant frequency is the approach taken in the magnetron designed for the SPS satellite, but is not a feature of the ordinary microwave oven magnetron. The first of the external means to impact the frequency is to simply vary the current through the tube which will change the frequency, but has the disadvantage that it also changes the power output of the MDA. This was the first approach that I used to demonstrate the feedback loop involving the phase comparator. The other external means is to vary the reactance of the load into which the MDA operates. This approach was successfully developed in a joint program between the NASA Center for Space Power at Texas A&M and the author in 1993.5
Because of possible confusion with respect to the various levels of MDA development and their ability to meet important performance criteria, the author has defined four classes of the MDA. These are given in Table 1.
As a result of the recent availability of class 3 and class 4 MDAs, the prospect of building low-cost electronically steerable arrays has been greatly improved. But it is essential that this fact be recognized, and such recognition is corning about through such demonstrations as the recent one in Chicago.
The use of the magnetron in the MDA has not compromised the attractive characteristics of the device which are its high efficiency (70%), its very high signal-to-noise ratio when run on a DC-filtered power supply, its long life of many years of continuous operation, its mechanical simplicity, which makes it easily produced, and, of course, its low cost. If anything, the performance efficiency of the device is better in the MDA than it is in the microwave oven.
The rectenna format that was demonstrated is also of interest for use in an Earthto-space power transmission system in which the satellites rotate around the equator and whose rectennas are illuminated with electronically-steerable arrays that sweep from West to East.6 Such a rectenna format needs to be highly nondirective in the West to East direction, but not in the North-South direction. The rectenna format in the demonstration exhibits these properties. The rectenna output excites four automobile electric lamps. When the rectenna is rotated about its horizontal axis, the lights retain their brilliance over a wide angle, but lose their brilliance rapidly when the rectenna is rotated about its vertical axis. The surrender of nondirective performance about one axis, makes it possible for many dipole elements to feed a single diode, which can then be isolated from the dipoles by a many element filter to prevent harmonic radiation from the rectenna.
The article concludes with a glance at the next milestone in the SSI program. That milestone will be the flight of an untethered microwave-powered helicopter, which automatically positions itself over the center of the microwave beam. Historically, a small tethered microwave-powered helicopter and an untethered but conventional-powered helicopter have been successfuly demonstrated as shown in Figures 6 and 7.7 The factor that now makes it economically possible to demonstrate an untethered microwave-powered helicopter, is the availability of small radio-controlled helicopters that are used by a surprisingly large group of hobbyists. The same SPAM (steerable phased array module) used in the horizontal demonstration will be pointed vertically and serve as a microwave beam power source for the helicopter.
In conclusion, it is noted that there are two SPAMs being used, one in Alaska and one in Massachusetts, to add redundancy to the development program. At some point in time it would be possible to bring these two together to demonstrate electronic steering of the microwave beam that is jointly generated by the two SPAMS.
1. William C. Brown, “Update on the Solar Power Satellite Transmitter Design,” Space Power, Volume 6, pp 123-135, 1986.
2. “Design Study for a Ground Microwave Power Transmission System for Use with a High-Altitude Powered Platform,” NASA Contractor Report 168344, June 1983, Contract No. NAS6-3200.
3. “Microwave Beamed Power Technology Improvement,” Final report, JPL Contract No. 955104, Raytheon Report PT-5613, May 15, 1980.
4. Edward David, “Phasing by rf Signals,” Crossed Field Devices, edit. Ernest Okress, Vol. 2, Academic Press, 1961.
5. William C. Brown, “Magnetron Directional Amplifier Development,” Final Report, Texas A&M Research Foundation, Subgrant No. L300060, Prime Grant No. NAGW-11194, Project RF-2500-95, February 23, 1994.
6. “A Transportronic Solution to the Problem of Interorbital Transportation,” Final Report NASA CR-191152, July 1992, Contract NAS3-25066.
7. “Experiments Involving a Microwave Beam to Power and Position a Helicopter,” IEEE Transactions on Aerospace and Electronic Systems, Vol. AES-5, No. 5, pp 692-702, Sept., 1969.
SSI CONFERENCE ON SPACE MANUFACTURING, MAY 4-7
In an effort to make the conference more accessible to our membership, we have changed from a Wednesday-Saturday format to a Thursday-Friday format. Each day will have presentations, demonstrations and activities involving a wide range of topics and formats. We hope that you and your family will plan to spend a few days with us in Princeton next spring.
Thursday morning will feature a keynote address (speaker to be announced), a morning session with formal presentations, and a demonstration of Dr. Brown’s wireless power transmission experiment. Following a luncheon, there will be an afternoon schedule of presentations. There will be a brief dinner break, and a roundtable discussion will make for an enlightening and entertaining evening.
Friday’s schedule will feature formal presentations in the morning and afternoon, a luncheon and wine and cheese reception at which the poster presentations will be highlighted.
Saturday will once again feature formal presentations followed by a luncheon and banquet. The banquet will be held at the Institute for Advanced Study. Cocktails will be served outside on the Institute grounds, weather permitting. Plan to join us and stroll the grounds where Einstein studied!
The speaker will be announced in an upcoming newsletter.
Sunday is a not-to-be-missed day! There will be a summary session in the morning at which all the papers will be summarized by the session chairs. The summary session will be followed by the traditional SSI box-lunch picnic at SSI headquarters. This is a chance for you to meet with many of the SSI researchers and staff, as well as the paper and poster presenters, in an informal setting. There will be wine and beer for the adults, soda for the children and, as always, plenty of ice cream for all!
Dr. John Lewis of the Lunar and Planetary Institute at the University of Arizona has agreed to chair this conference. Dr. Lewis is well known and well respected in the space research community, and he has attended every conference for the past ten years. He admits to a special affinity for Princeton in the spring. He spent his four undergraduate years here, and then went on to earn his advanced degrees from Dartmouth College and the University of California, San Diego.
Scope and Intended Audience
The High Frontier Conference is a biennial forum for the exchange of information about the advances in space technologies, programs and concepts. The conference will attract engineers, researchers, architects, builders, educators, lawyers, economists, sociologists and others interested in the development and settlement of space.
A tentative list of sessions follows:
• Extraterrestrial Resources
• Lunar Bases
• Space Manufacturing
• Social Sciences
• Biomedical Topics
• Space Settlements
• Space Structures
• Energy from Space
• Space Transportation
• Legal and Economic Issues
January 18, 1995 Abstracts due
February 17, 1995 Acceptances issued
April 17, 1995 Final papers due
May 4-7, 1995 Conference
Call For Papers
The Space Studies Institute hereby solicits papers that substantially detail recent and current work in any topic relevant to the field of space manufacturing, space development and space settlement.
1. The information should be new, or the paper should be a significant synthesis of existing information.
2. The abstracts should describe how much of the work has been completed and how much will be accomplished by the final submission.
All presenters must prepare an abstract for their presentation.
1. The abstract should be between 300 and 600 words, on 8.5 x 11 paper. One additional page of graphics may be submitted for review.
2. Please submit: two (2) copies of the abstract including names, affiliations, addresses and phone numbers of all authors.
3. Submit abstracts to: by US mail: Space Studies Institute P.O. Box 82 Princeton, NJ 08542 . By Fed Ex: Space Studies Institute 5 Crescent Avenue Rocky Hill, NJ 08553
A registration fee of $340 includes lunches, coffee breaks, the Saturday night banquet, Sunday afternoon picnic, a hard-bound copy of the proceedings and admission to all sessions. For early registration (before April 15), the fee is $325. Call the Space Studies Institute to receive a registration packet
About the Institute
BOARD OF DIRECTORS
Dr. Roger O’Neill, Chairman
Prof. Freeman Dyson, President
Dr. Joseph P. Allen
Mr. Junta Ayukawa
Mr. James Burke
Mr. Morris Hornik
Mr. Gregg Maryniak
Mr. William O’Boyle
Dr. Fred Rose
Dr. Lee Valentine
BOARD OF GOVERNING MEMBERS
Mr. James Burke
Prof. Freeman Dyson
Mr. W. Brandt Goldsworthy
Ms. Bettie Greber, Executive Director
Mr. James Laramie
Mr. Gregg Maryniak
Mr. William O’Boyle
Ms. Tasha O’Neill
Dr. David Odom
Dr. Fred Rose
Dr. Lee Valentine
Mr. David Wine
BOARD OF SENIOR ADVISORS
Col. J. Paul Barringer
Barringer Crater Company
Mr. Richard Boudreault
Dr. William Brown
Mr. Christopher J.
Faranetta NPO Energia, Ltd.
Dr. George Friedman
Mr. George Gallup, Jr.
Mr. Richard E. Gertsch
Colorado School of Mines
Mr. Alex Gimarc
Dr. Peter Glaser
Mr. James Harford
Ms. Kathy Keeton
Mr. Jeffrey Manber
NPO Energia, Ltd.
Dr. Rashmi Mayur
Mr. Burt Rutan
Scaled Composites, Inc.
Mr. Steven Vetter
The Space Studies Institute is a nonprofit, international, research and educational organization. Founded in 1977, it is dedicated to opening the high frontier of space.
SSI’s goals include using the material wealth and solar energy of space to improve the human condition both for those who live on Earth and those who live in space, and to build Earth-like habitats in space to expand the ecological range of humanity throughout the solar system and ultimately, perhaps, throughout the galaxy.
To this end, SSI has conducted and is conducting pioneering research into advanced space propulsion, the extraction and processing of nonterrestrial materials for engineering purposes, and the identification and location of lunar and asteroidal resources.
Following are four opportunities for participation in SSI activities:
SSI’s Corporate Membership program offers access to SSI’s broad base of technical advisors, access to a resume pool, and access to exhibit space at the biennial SSI Conference on Space Manufacturing. Research partnerships are encouraged.
Senior Associate Program
The Senior Associates Program is currently SSI’s largest source of funds for High Frontier research and education. The program also provides a way for anyone interested in the High Frontier to play a key role in making space colonization and space manufacturing achievable within our lifetimes.
Following is a description of the program.
The Senior Associate program was created in 1979 to generate the steady funds that SSI needs to conduct research projects, most of which require money for several years. Today we have about 1,000 active Senior Associates; 537 Senior Associates are on their second, third, or fourth pledge. The program provides about 60% of SSI’s annual budget and is essential to both our research and educational activities.
Senior Associates receive special benefits as our thanks for their support. These benefits include invitations to special events, free mailings of publications by SSI, NASA, and other space organizations; and confidential newsletters, describing SSI developments before they are made public.
However, most people become Senior Associates because they want to see space colonization become a reality; they give muchneeded funds and join the group of people working to create the High Frontier in our lifetimes. As Senior Associates, they also meet others who share their enthusiasm for space exploration and development. Each Senior Associate makes a five-year pledge to SSI, choosing one of the ranks below:
Associate: $100.00 annually
Fellow: $200.00 annually
Colleague: $300.00 annually
Distinguished Collegue: $500.00 annually
Payments can be made annually, semiannually, quarterly, or monthly.
Each Senior Associate receives a number with his or her rank, indicating when he or she joined the program. For example, the next person to join could become Fellow 368, or Distinguished Colleague 126. Each Senior Associate receives a certificate, signed by SSI’s president, as a permanent record that he or she was one of the first people who gave critical support to the High Frontier. The names of the Senior Associates will also be permanently maintained by SSI to provide historians with the names of early High Frontier supporters.
SSI Membership is open to individuals worldwide. All members receive the Institute’s newsletter, which is published bimonthly and keeps all SSI members abreast of SSI research, an SSI membership card and decal. Membership fee: Regular $25.00; Senior Citizen or Student $15.00; non-US addresses, please add $10.00.
For gifts of $50.00 or more, you will receive an SSI lapel pin.
With gifts of $100.00 or more, you will receive a copy of Dr. O’Neill’s book, The High Frontier.
As a nonprofit organization, SSI relies on the expertise of many volunteers worldwide to assist in the areas of research, education, presentations, development of visual arts, and technical writing.
If you are interested in the future in space, contact SSI by letter, phone, FAX, or E-mail the Space Studies Institute.
©space studies institute
NEXT: 1994 Nov-Dec (William Brown receives IEEE Pioneer Award, Leik Myrabo on Microwave Launces of Small Payloads)
SSI Newsletters: 1994 September October
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