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APPENDIX II POTENTIAL APPLICATION OF ELECTRON-OPTICAL METHODS TO STORAGE OF INFORMATION FOR DIRECT RETRIEVAL H. FERNANDEZ-MORAN The basic problem limiting the information retrieval envisaged from Mars or any other planetary mission seems to be the limit to the bits of information obtainable, of the order of about 109 bits of information, that is given by inherent telemetry parameters. There is also a long time- interval involved. These limitations impose severe restrictions on the design of any type of system for the detection of extraterrestrial life. It is therefore suggested that the development of a miniature microscope may also be of critical importance from the point of view of information condensation and retrieval. It has been demonstrated that the electron microscope cannot only be used to magnify but also to faithfully demagnify images several thousandfold [Mollenstedt and Speidel, 1960; Ferndndez- Mordn, 1959]. In our case, we used a commercial electron microscope (Siemens Elmiskop) with a pointed filament source to produce very small microbeams of 100 to 1,000 A diameter to write and print out letters and diagrams which were only a few microns to a few hundred A in size (Figure 1). This printing was done on specially developed ultrafine grain films of silver halide (silver iodide and silver bromide with crystallites of the order of 100 A; film thickness about 100-200 A). Mollenstedt achieved the same results by a more complicated device involving modifications induced in a plastic film which were subsequently brought out by shadow casting. (Figure 2). This means that one could record any type of information 503

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504 APPENDIX II • '.. . -j f Figure 1. Electron micrograph of ultramima- turized circuit patterns produced by photoengraving with electron micro- beam probes (500 to 1,000 A diame- ter) on special ultrafine photographic film. XI 0,000. Figure 2. Miniaturized letters (of less than 1 micron) engraved on thin collodion film using electron microbeam probes produced by demagnification in an electron microscope [Mollenstedt and Speidel, I960]. X20,000. from letters to diagrams to oscilloscope signals, etc., in such a way that, in the optimal case, the contents of several million volumes of books can be condensed on an area of a single page size or its equivalent.. Therefore, this miniature microscope approach appears to be, in general, applicable to the whole problem of information collection, storage, and retrieval which is a critical bottleneck in extraterrestrial studies. Specifically, it is proposed that all of the information obtained during the Mars missions and other extraterrestrial missions be considerably con- densed by electron optical demagnification (ratio of demagnification, 1:1,000 to 1:50,000 or more). This would mean that bits of information, greater in number by several orders of magnitude, can be imprinted directly onto reels of special ultrathin tape by demagnification electron microscopy. The ultrathin tape of silver halide is about 100-200 A thick and can be mounted on suitable resistant thin tapes of rhenium, tantalum, or other refractory material. The amount of information that could be recorded in a tape reel with a total area the size of a typewritten page varies from the content of a 1,000,000 volume library (each volume, 500 pages) to approximately a 10,000,000 volume library. A roll of this ultra- microtape after recording would be wound onto a bobbin of only a few cubic centimeters at most. This bobbin could be detached and provided with its own rocket propulsion (plasma or other type of propulsion that is

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Storage of Information for Direct Retrieval 505 practical and long-lived for such a small object) and with a radio beacon or other device to indicate and monitor its presence and trajectory. This "space courier pigeon" (in analogy to the earlier uses of microfilm trans- mission by pigeon courier post) would be programmed to "home," back to Earth, by making use of optimized navigational techniques. Once within the reach of our Earth or outer space retrieval capabilities, these microtape capsules could be directly retrieved and read-out in space. This is of particular importance in view of the possible contamination danger. Also, attempts to bring back the capsule would probably involve prohibitively large devices to prevent its burning up upon reentry. It is realized that the problem of retrieval is complex. However, many of these capsules could be sent, or many copies of the first one made immediately and distributed to enlarge the margin of retrievability through redundancy. The problem of demagnification of the image could be approached in several possible ways: (a) Either the vidicon image can be made to scan directly, using electron microbeams and electron optical demagnification through a permanently attached miniaturized electron microscope, operating in reverse, so as to print directly on the very fine photographic film which would be slowly unrolled from the tapes. It should be noted that from our experience, extending over more than five years, once printed, these silver halide films, which are of the direct print-out type and need no further development or fixation, are very stable to radiation and preserve detail of the order of about 100 A quite clearly. This type of recording a television image onto an area only a few square microns in size would be ideal since the direct television image, with a larger number of bits than can be presently obtained, then can be read-out back on Earth or on space platforms with a converted electron microscope and image intensifier. (b) The alternative would be to use the principle of advanced electron beam recording techniques such as those developed at General Electric by Newberry [1963] or some other type of ultraoscilloscope recording, not only for vidicon recording but for recording of all other types of informa- tion. A critical analysis of this admittedly rather speculative proposal reveals that the main operational problem would be one of retrieval. It remains to be demonstrated that it is feasible that an object only a few cubic inches or a few cubic feet at most, if provided with sufficiently compact power supply and navigational aids, can navigate back to Earth with some measure of reliability. It might be asked whether it could escape first order perturba- tion influences on the way and be literally led "astray." Even if it approached Earth and could make a rendezvous with a space platform or with a large type of satellite, can the read-out mechanism function reliably

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506 APPENDIX II enough that it can be automated? Many of these questions are outside of the domain of our present experience, but it is perhaps conceivable that by the time this concept is ready to be applied, we will be far enough advanced in our space technology to have space platforms which are manned. Under these conditions, retrieval of the space pigeon (alternative name: "Minicomp" or "Minicompo" system) becomes much more practical. Actually, the main problem here resolves itself into the basic question, "Is the expected gain in information storage and retrieval worth the whole effort?" Here, the answer is undoubtedly, "Yes." First of all, there is no telemetry device that could conceivably carry this amount of information (of the order of 101G to 1020 bits) and provide truly significant data retrieval with a sufficiently high signal-to-noise ratio in an economical and reliable fashion, as the described micro-recorded image. Even if manned space flights to Mars become feasible, the use of information packages of this type is just as necessary as in today's communication network. No amount of teletype, telephone, or even television, can replace the letter, the book, drawings, pictures, blueprints, etc. This problem will become even more acute as the distances to other planets and surrounding perturbations (magnetic field, sunspots, etc.) make direct electromagnetic radio communications very long or actually impossible. Sooner or later, we will have to develop some type of compact, condensed, ultraminiaturized information storage and retrieval system. It will also be one of the safest ways of sampling alien environments with a minimum of cross-contamination, since a great deal of information can be recorded and transmitted without effecting actual bodily contact. It should be noted that development of this idea on Earth is already of key significance in order to cope with the critical problem of information condensation and retrieval under the conditions of the present "information explosion." With all of these considerations in mind, it is suggested that this type of approach be given serious consideration and assigned a rea- sonably high priority since it merits a determined and concerted effort. REFERENCES Fernandez-Moran, H. (1959), Studies of the Effects of Ionizing Radiation on the Ultrastructure of Developing Nervous Tissue as Revealed by Electron Microscopy. Annual Rept. for U. S. Atomic Energy Comm. Res. Contract AT(30-I)-2278 for Period Nov. 1, 1958 to Oct. 31, 1959. Mollenstedt, G., and R. Speidel (1960), Elektronenoptischer Mikroschreiber unter Elektronenmikroskopischer Arbeitskontrolle. Phys. Blat. 16, 192-198. Newberry, S. P., E. C. Buschmann and T. H. Klotz (1963), Advanced Electron Beam Recording Techniques: Final Report. RADC-TDR-63-234, Rome Air Development Center, Griffiss AFB, N. Y.