Jonathan Vos Post, C.E.O.
Computer Futures Inc.
3225 North Marengo Avenue
Altadena, California 91001
U.S.A.



FUTURE SPACECRAFT SENSORS

by

Jonathan Vos Post

(c) 1991 by Emerald City Publishing A Speculative Nonfiction Article of Approx. 6,000 Words which appeared in Quantum Science Fiction Review

Topics covered (after an introduction): focal plane arrays the size of billboards; holographic imaging of planets illuminated from Earth by laser; sonar systems deep in the oceans of the Jovian moon Europa; Synthetic Aperture Radar with antennas a mile across; high temperature superconductor SQUIDS that can find, from orbit, the magnetic anomaly of sunken ships at sea; and phase-locked optical arrays that can directly image cloud patterns on planets in other solar systems. Robert Forward mass detectors remotely weighing asteroids and comet nuclei during flybys; gravity wave detectors listening for the scream of stars falling into black holes; biosensors sniffing space for the smell of rare interstellar molecules; vast arrays of neutrino detectors on the far side of the moon, and embedded in the polar dry ice caps of Mars; Cerenkov photodetectors searching for the flash of faster-than-light tachyons from the Big Bang; Zero-Point Energy lurking in supposedly empty space; nanotechnology devices deconstructing specks of interstellar dust to understand local cosmochemistry and to search for pollution from extraterrestrial civilizations; and, speaking of extraterrestrials, huge infrared and millimeter wave sensors looking in other solar systems for stray radiation from artificial construction projects larger than planets. e-mail to the author?
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INTRODUCTION

Most of the editors I know live a trillion miles away. I mail stories, editorials, novels, and book proposals to them and get a reply in about four months. My theory is that their editorial offices digitize my submissions and beam them to the editors' secret residences, somewhere out in the Oort cloud of comets, far beyond the orbit of Pluto. The editors, strange beings that sometimes pass for human when they visit Earth to attend conventions, formulate their replies with phrases such as "clever, well-written, but not quite right for me" and beam them back. A light year is roughly six trillion miles, so a round-trip distance of two trillion miles would account for a 1/3 year delay, hence my estimate of a one-way distance of a trillion miles. My wife, the beautiful and talented Dr. Christine Carmichael, insisted on the opening phrase "most of the editors I know," pointing out that most editors probably live thirty thousand light years away. Presuming, of course, that the Milky Way galaxy is filled with civilization, mostly concentrated in towards the nucleus. The good news is that a galactic best-seller might be read by an audience of trillions or quadrillions. The bad new is that the royalty check won't arrive until sixty thousand years after the manuscript is submitted. So how can a writer find one of the elusive trans-Plutonian editors? Focal plane arrays the size of billboards? Holographic imaging? Synthetic Aperture Radar? High temperature superconductor SQUIDS? Forward mass detectors? Gravity wave detectors? Biosensors? Neutrino detectors? Tachyon Cerenkov photodetectors? Nanotechnology? Infrared and millimeter wave sensors? That leads us to the topic of Future Spacecraft Sensors. I didn't choose the topic. It chose me. On 29 August 1991 I got a phone call from Gerald Godden of The Analytical Sciences Corporation in Arlington, Virginia. Gerald Godden was seeking a speaker for the American Institute of Aeronautics and Astronautics (AIAA) Conference in Reno, Nevada, 6 January 1992. It would be the keynote speech in a special presentation "Images from Space: Yesterday, Today, and Tomorrow" in recognition of International Space Year (1992), and would be sponsored by the AIAA Sensors Systems Technical Committee. The Committee wanted someone who was known to give a dazzlingly witty and professional presentation on the role of sensors in (1) guidance and navigation, (2) space exploration, and (3) exploration and mapping of the Earth from space. Edwin Kilgore and Dr. Joe Alexander agreed to focus on NASA missions of the past and present, but who could outline the future? Dr. James B. Stephens of the Jet Propulsion Laboratory, one of the three most prolific inventors in Caltech's 100 year history, was called to recommend a speaker. Jim Stephens is perhaps the most brilliant technical jack-of-all-trades I've ever met. Since he's arranged consulting jobs now and then for my wife and myself, he's acquainted with my technical expertise. Fortunately, he's also a science fiction enthusiast. "Get a science fiction author who's also a scientist," he said, or words to that effect. "Why don't you ask Jonathan V. Post?" I found myself trying to convince Godden that the future of spacecraft sensors is so incredible that I intended to outline that future, using as my credentials not my membership in AIAA, but in Science Fiction Writers of America. "After all, I said, "science fiction author Arthur C. Clarke invented the geosynchronous communications satellite, Ph.D. astrophysicist writers Gregory Benford and David Brin correctly predicted the size of the Halley's Comet nucleus in the novel "Heart of the Comet", science fiction novelist Thomas McDonough (author of "The Architects of Hyperspace" and January 1992's release of "Missing Matter") predicted the ion torus around Jupiter..." "But we're asking you," said Godden. "What was your best- seller, and what have you predicted?" "I haven't had a best-seller..." I said, teeth clenched, "yet. I did publish the 1980 prediction in Omni Magazine that we would find a giant black hole in the center of our Milky Way, and the 1979 prediction in Omni that we would have a fierce political debate over a new generation of space-based antiballistic missile defenses (now known by the science fiction name of "Star Wars"). For that matter, I had a story "Skiing the Methane Snows of Pluto" in Volume 1, Number 1 of Focus, the magazine of the British Science Fiction Association. In this story, I explicitly predicted -- years before the Voyager spacecraft provided dramatic confirmation -- volcanos on Io, the tectonically active pizza- colored moon of Jupiter." "That might be a lucky guess," said Godden. "Anything else?" "A lucky guess? Well, maybe," I agreed. "But luck is context sensitive. After all, I wrote an outline for a novel in July 1987 that no publisher wanted to buy. In August 1991, I got a $15,000 advance for it. Why? Because it had revolved around Gorbachev being ousted in a coup, and then coming back to power. And it also had a character who picked up strange signals from the Deep Space Network at JPL, though my friend Robert Cesarone (expert in interplanetary and interstellar trajectories) just this month became Manager of Strategic Planning for the Deep Space Network. So set your critical faculties aside. Throw your skepticism on the craps tables where it belongs. Let's look to the future as if it were a story in what used to be called Astounding and is now Analog. And can I tell you about a magazine called Quantum?" Godden was won over, but he still had to persuade the rest of The Committee. We agreed on a conference call the next morning, with a G. Lindgren, an S. Schwartz, and an S. Welch. What I did first was get up before the crack of dawn (which cracks pretty early in mid-summer) and dash off 3600 words of speculation, based on all the neat stuff I'd read and couldn't lay my hands on right away. The Committee was still skeptical. "Exactly what did you co-author and publish with Ray Bradbury and with the late Nobel Laureate Richard Feynman?" "Poems." "Who says we want a poet for a keynote speaker?" So I faxed them the manuscript, plus a $36 bill for the laserwriting and faxing. They agreed to let me give the speech. The check arrived at the end of October. Two months. That's progress for you. Now I was dealing with entities only half a trillion miles away. This is a longer introduction than most nonfiction essays get, and will again infuriate Quantum readers who hate autobiographical details. The rest of the readers deserve a chance to know how life really works at the boundary of science and fiction. Before we finally get to the bizarre technical details, let me give you a taste of what we'll be discussing: focal plane arrays the size of billboards; holographic imaging of planets illuminated from Earth by laser; sonar systems deep in the oceans of the Jovian moon Europa; Synthetic Aperture Radar with antennas a mile across; high temperature superconductor SQUIDS that can find, from orbit, the magnetic anomaly of sunken ships at sea; and phase-locked optical arrays that can directly image cloud patterns on planets in other solar systems. Far out? Bizarre? But that's only the beginning. We'll go on from there to look at even more exotic spacecraft sensors of the 21st century and beyond: Robert Forward mass detectors remotely weighing asteroids and comet nuclei during flybys; gravity wave detectors listening for the scream of stars falling into black holes; biosensors sniffing space for the smell of rare interstellar molecules; vast arrays of neutrino detectors on the far side of the moon, and embedded in the polar dry ice caps of Mars; Cerenkov photodetectors searching for the flash of faster-than-light tachyons from the Big Bang; Zero-Point Energy lurking in supposedly empty space; nanotechnology devices deconstructing specks of interstellar dust to understand local cosmochemistry and to search for pollution from extraterrestrial civilizations; and, speaking of extraterrestrials, huge infrared and millimeter wave sensors looking in other solar systems for stray radiation from artificial construction projects larger than planets. There, are you in the mood now for some technologically advanced space sensors of the future? Good. But let's put some meat on the bones, and get into some of the juicy details.
IMAGING
Airborne Remote Sensors will push the state of the art for spaceborne sensors in at least one area. After the borders of the U.S. will be successfully sealed against drug smuggling from South America, the Drug Enforcement Agency will be flying biosensor sniffers, remote imaging systems, and multispectral analyzers to seek out illegal plantings of home-grown cocaine in the Rocky Mountains and the Cascades. The cross-fertilization between military and civilian air-borne and space-borne technologies will accelerate. ECM and ECCM, for instance. Electronic Surveillance, Electronic Countermeasures, and Electronic Counter-countermeasures will be in orbit to protect us from the greatest threat of all: the evil empire of international banks including a revived B.C.C.I. and the stealthy trillion dollar secret bank accounts in Switzerland. Watch out for those Gnomes of Zurich! Allen Steele, in the novel "Orbital Decay," postulated antennas in orbit for covertly picking up individual telephone calls. If you want to feel paranoid, how do you know that these don't exist already? Electromagnetic Pulse (EMP) will also be a threat. Not only is it a terrible consequence of nuclear war, but EMP would fry the delicate circuitry of our beloved space sensors. But that will never come to pass. Citizens may yawn at the threat of cities being vaporized, but when you tell them that EMP will kill their personal computers, they write angry letters to their congressmen. What's the real reason for the sudden wave of nuclear disarmament? Could it be the new team of Apple and IBM? I don't really know. But I do have a cute idea in that novel about Gorby, Yeltsin, and the Counter-Coup. A vivid imagination makes up for a whole lot of fuzzy vision. Speaking of vision...
FOCAL PLANE ARRAYS
Focal Plane Arrays are getting bigger and bigger, both in sheer physical size and in the number of pixels of resolution. These are the heart of space-based telescopes and cameras, and will be for a generation to come. Projecting current trends into the 21st century we can expect to see arrays of a million by a million active elements, spread over a substrate with the area of a small parking lot. Of course, the optics that focus light, infrared, and ultraviolet onto these arrays will not be lenses the size and shape of flying saucers. The optics will be flat fresnel lenses manufactured in space of vacuum-deposited diamond crystal. Imaging will be good enough, and cheap enough, that anyone can log into his or her computer network and call up a real-time display of any point on the surface of the Earth with a resolution of one centimeter. This is the official prediction of the Defense Mapping Agency, thereby guaranteeing themselves a steady growth in employment. Of course, since the surface area of the Earth is 10 to the poer of 18 square centimeters, this will require some pretty fancy data compression, and a hyper-large database. Some people won't like the loss of privacy from their being identifiable from orbit. Others will wear mirrors hanging at 45 degree angles on their chests so that their pretty faces will be clearly visible from hundreds of miles straight up.
LIDAR AND ACTIVE OPTICS
Laser Radar (LIDAR) will be extremely important for accurate measurement of distance, altimetry, and doppler ranging of relative velocity. Repeatedly remeasured altitudes of geographical points on Earth to a sub-millimeter resolution may be an effective means for Earthquake early warning. Space-based LIDAR may replace today's ground-based air traffic control systems, although not currently a part of the Federal Administration Agency's AAS -- Advanced Automation System -- for the year 2000 and beyond. I worked on the Hughes Aircraft AAS proposal, and discovered that the FAA is far more interested in building ground-based systems in the districts of key Congressmen. Using active optics, mirrors that change their shape in real- time to compensate for atmospheric aberration, laser beams can be sent to the planets from sites on the surface of the Earth. But the availability of cheap solar power in orbit suggests that the really big lasers may be based in orbit or on the moon. These big lasers will be able to directly iluminate moons, planets, and asteroids so that fly-by spacecraft with their own laser systems can create high resolution holograms. Space holograms may also be a critical means of tracking sub-centimeter fragments of deadly space junk in low Earth orbit, and of resolving the pattern of particles in the asteroid belt and in the rings of Jupiter, Saturn, Uranus and Neptune. Speaking of those outer planets, NASA hopes not only to launch in 1996 the Cassini mission to orbit Saturn and drop a probe into the atmosphere of Titan, but also hopes for the CRAF (Comet Rendezvous/Asteroid Flyby) spacecraft as well as systems orbiting Uranus, Neptune, and possibly Pluto in the early 21st Century. These spacecraft will be exciting opportunities for the space sensors now under development. Remind me to tell you some other time how I led the biggest pro-space rally in U.S. history, where some 50 dedicated citizens chanted "Don't be a weenie, vote for CRAF/Cassini."
EUROPA AND TELECOM
Sonar systems can provide effective imaging in lightless conditions deep below the surface of bodies of fluid. Perhaps the most mysterious place in the Solar System can be found beneath the cracked icy crust of the Jovian moon Europa. Planetary Scientists believe that under the ice there is probably a liquid water ocean more than a thousand miles deep. Arthur C. Clarke has already speculated on Europa in the book and movie "2010." He told me that he's waiting to write another book in the "2001 Space Odyssey" series in which Europa will play a major role, but will prudently wait until the Galileo spacecraft arrives in Jupiter orbit in 1995. Future space submarines will cruise through the incredible pressures of this ocean, sending their data back to the surface by fiber optics. And so a totally new class of space sensors will someday bring us secrets from deep in the oceans of Europa. Synthetic Aperture Radar and conventional parabolic dish radar is limited only by the size of its antenna. James B. Stephens of JPL has filed a patent for an inflatable sphere with integral solar power arrays and with distributed active antennas whose aperture is a mile across. The echo satellite in orbit over 30 years ago looks like an idea ahead of its time, but Echo was passive. The active system could change the telecommunications future radically. Jim recently brought Edward Teller and Solar Power Satellite inventor Peter Glaser into a consortium to develop the idea. More on this when the patent papers are approved.
SQUIDS IN SPACE AND BRAINS
Magnetic Field Sensors will become far more sensitive with the use of high temperature superconductor SQUIDS (Superconducting Quantum Interference Devices). Old fashioned cryogenic superconductors have a somewhat better signal to noise ration, but ceramic high temperature superconductors save so much weight by eliminating the liquid helium systems that they will predominate in space-based applications. Spaceborne SQUIDS might just able to find, from orbit, the magnetic anomaly of sunken ships, airplanes, and submarines at sea. J. E. Zimmerman, in the "Low Frequency Superconducting Sensors" chapter of "The Role of Superconductivity in the Space Program" (NASA-NBS, 1978) suggested that a pair of SQUID magnetometer satellites in orbit a hundred kilometers apart could act as a very long baseline gradiometer, able to find underground ore bodies a kilometer in radius. Professor Jan Garmany (Institute for Geophysics, University of Texas at Austin) agreed with my more extravagant prediction about sunken metal artifacts, but said that the satellites should orbit much more closely together and that mapping midocean ridge magnetic reversal stripes should be the priority. On the other hand, it has already been demonstrated that SQUIDS help solve a biomedical sensor problem. To look into the activity of the human brain, traditional technique involves arrays of electrical sensors. The older approach used platinum electrodes sticking through the scalp right into the brain, but Derek Fender and his colleages at Caltech developed arrays of dozens of sensors that can be attached outside the skull. The problem is with the electromagnetic interference that comes from twitching scalp muscles. But, as I've detailed in my short story "BrainSails", SQUIDS have proven effective in sensing the tiny magnetic fields of working brain cells. So future manned spacecraft may very well have SQUID helmets on the astronauts that, in essence, read the minds of pilots and payload specialists to control instruments some 200 milliseconds before a hand could start to move or a voice begin to speak. Imagine the strange sensation of using a SQUID helmet word processor, in which your words appear on the screen before you're consciously aware that you've chosen those words at all. Perhaps the obstacle will be psychological -- we'll need to crack the "deja vu barrier."
LOOKING AT OTHER SOLAR SYSTEMS
Phase-locked optical arrays of viusible, infrared, and ultraviolet telescopes on the Moon can, if the array is some twenty kilometers across, directly image cloud patterns on planets in other solar systems. Putting spectrometers at the focus of these telescopes will allow direct measurement of the chemical composition of those planets. And we all know what it means if we detect the concentrations of free oxygen that can only be released by biological systems, or for that matter if we detect chloroflurocarbons, or even plain old smog...
X-RAYS, GAMMA RAYS, AXAF, AND GRO
X-Ray and Gamma Ray Sensors will also play a significant role in space science of the future, beginning with the AXAF and GRO satellites, and observing the most violent events in the universe through elecromagnetic radiation of the shortest wavelenths and highest frequencies. It is interesting to note the material science challenges of working with some X-Ray and Gamma Ray sensor materials such as frozen solid lumps of ultrapure inert Xenon. It is also interesting to note the new type of X-ray lens developed by a Soviet scientists which consists of hundreds of thousands of hollow optical fibers welded together and deformed. New sensors will take advantage of these new materials and designs. But future space sensors will range far beyond the limits of the electromagnetic spectrum. Let's look at some of the far out examples.
MASS DETECTORS AND GRAVITY WAVES
Mass Detectors exploit general relativity to allow remote measurement of nearby masses. These are called Forward Mass Detectors, not because they can't look backwards, but because they were invented and patented by science fiction novelist Dr. Robert Forward, formerly Senior Scientist of the Hughes Malibu Research Center. First popularly described in the stories of science fiction writer Larry Niven, these mass detectors are capable of remotely weighing asteroids and comet nuclei during flybys. Gravity Wave Detectors have been a source of controversy since Einstein predicted them and Dr. Weber at the University of Maryland first constructed one in the late 1960s. In fact Robert Forward started as a technician for Dr. Weber, long before he became well-known to AIAA members for his design of the 10- gram "StarWisp" interstellar proble propelled by quadrillions of watts of microwave power from solar power satellites near the orbit of Mercury. Able to detect quadrupole radiation from large accelerating masses, gravity wave detectors will be listening for the scream of stars falling into black holes, for the distinctive signatures of supernovas and, as I first pointed out in Omni a dozen years ago, will be able to sense from 100,000 light years away the signals of a "gravity wave telegraph" with dots and dashes consisting of small and large asteroids being dropped into a star.
INERTIAL MEASUREMENT UNITS ANFD GUIDED BULLETS
Einstein established, in General Relativity, that gravity and inertia are equivalent. Exact measurement of inertia is what spacecraft designers demand from gyroscopes and accelerometers. Inertial Measurement Units (IMUs) used to weigh in the neighborhood of a hundred pounds. One breakthough came when coils of optical fibers proved to do the job of spinning metal wheels, reducing the weight of IMUs to a couple of pounds. The new goal for the year 2000 is the gyroscope on a chip. Gyrocompasses made of miniaturized tuning forks have shrunken to the size of golfballs, already important to guided missile navigation. When both the inertial sensor and the analysis electronics are reduced to the same chip of silicon, the cost in quantity could drop to around ten dollars. "Once you get a gyro and an accelerameter on a chip, you can let your imagination run" says consultant Robert G. Brown ("Advances on the Gyroscope Front", Andrew Pollack, New York Times, 30 Oct 91, p.C7). Experts predict cheap antiskid systems for automobiles, precise positioning of surgical instruments, steadying lenses on camcorders ... and guided missiles so small that they might better be called "guided bullets." For spacecraft designers, that opens the door to planetary microspacecraft so small that thousands or even millions could be launched by a single big booster and shotgunned out into the solar system. It also means that interplanetary spacecraft weighing a pound or less can be launched by cheap, small commercial rockets; or by railguns, hydrogen gas guns, or other cheap non-rocket launch systems of the early 21st century. The message is: keep shrinking every category of spacecraft sensors to take advantage of the opportunity. Single organic cells have sensors, analog computers, and actuators in a space a few microns wide, after all. Think small!
Biosensors, also known as Biochips, are electronic devices with thin coatings of sensitive organic chemicals. They respond to extremely low concentrations of specific materials. One Japanese researcher has already demonstrated a sensor which can distinguish fresh fish from not-so-fresh fish, and the military are very involved in biosensors to detect trace amounts of nerve gas or the emissions from hidden explosives. The space-based applications will be extremely important for determining the chemical composition of comets and carbonaceous chondrite asteroids, and also for sniffing space to detect the smell of rare interstellar molecules.
NEUTRINO TELESCOPES
Neutrino detectors have not been deployed in space so far. That's because these tiny uncharged nearly massless particles travel like ghosts through tremendous volumes of material with only very rare collisions. Neutrino detectors on Earth have typically involved hundreds of thousands of gallons of chlorinated hydrocarbons shielded from charged cosmic rays by being placed in salt mines and other sites a mile below the Earth's surface. However, a recent proposal suggests placing neutrino detectors on the far side of the Moon, and using the Superconducting Supercollider to shoot a beam of neutrinos right through the moon to those sensors. This will help solve the myustery of why we sense only a third of the neutrinos that we expect to be produced in the core of the sun. I have a paper coming out this spring in the Proceedings of Space-92: Engineering, Construction, and Operations in Space in Colorado about the challenges of constructing vast arrays of neutrino detectors on the far side of the moon, and embedded in the polar dry ice caps of Mars. Ken Lander (University of Pennsylvania) first proposed putting neutrino detectors on the far side of the Moon to help solve the mystery of the solar neutrino deficit by firing neutrinos from Earth right through the Moon to these detectors ("Shooting the Moon to find missing neutrinos, New Scientist, 5 January 1991, p.14). Francis Halzen (University of Wisconsin) plans to turn a cubic kilometer of Antarctica into a neutrino telescope ("Ice telescope could detect cosmic neutrinos", New Scientist, 16 February 1991, p.24). I have extended their ideas into an approach for building neutrino detectors inside lunar liquid oxygen tanks to establish interferometery, and to building a Martian polar cap neutrino detector for Earth-made, solar, and cosmic neutrino measurement at a significant baseline distance from the Earth-Moon system. I have also suggested that neutrino detection and gravity wave measurement offer an alternative approach to SETI (Search for Extraterrestrial Intelligence) independent of electromagentic radiation.
TACHYONS: FASTER THAN LIGHT
Cerenkov Photodetectors are an established means for sensing charged particles moving faster than light can move in a solid or liquid medium. The familar blue glow of underwater nuclear reactor fuel rods comes from Cerenkov radiation. But Gerald Feinberg and other scientists pointed out some 20 years ago that it might be possible to see Cerenkov radiation in a vacuum, if that vacuum is being crossed by charged particles that move faster than light can travel in a vacuum. Future space sensors may therefore be searching for the flash of faster-than-light tachyons from exotic sources such as the Big Bang.
ENERGY IN THE VACUUM?
Speaking of weirdness lurking in vacuums, a long-standing mystery in Physics is the so-called electromagnetic Zero-Point Energy (ZPE). Quantum mechanics informs us that the vacuum is filled with enormous amounts of energy, even at absolute zero temperature. Physicists once calculated that ZPE was actually infinite, but even when they imposed cut-offs at high frequency, the energy density of "empty space" seemed to be about as high as the energy density inside an atomic nucleus. If we can extract energy from nuclei, why not from extract energy from the vacuum? Well, that's an Engineering problem. ZPE is not just a mathematical notion, but has observable consequences. ZPE subtly perturbs electrons in atoms so that when they jump from one state to another and emit photons, we can measure the "Lamb shift" of the resulting spectral lines. The Casimir effect is a measurable attraction between closely spaced metal plates. Some wavelengths of electromagnetic fields are excluded by the close spacing, and the ZPE radiation pressure pushes the plates together. In between the plates, light travels ever so slightly faster. The scientific problem of ZPE is: where does it come from? One theory is that it's merely one of the "passive boundary conditions" of the universe, left over from the big bang. Others think that is "dynamically generated by the motion of charged particles throughout the universe which are themselves undergoing ZPE-induced motion." Harold E. Puthoff (Institute for Advanced Studies at Austin) proved that the second theory is more likely to be true, although he admits that it sounds "not unlike a cat chasing its own tail." What makes this important to spacecraft sensors is that the exact ZPE spectrum depends upon the size of the universe and the average density of matter in the universe. Careful ZPE measurements in vacuums far from Earth may tell us about the "cosmological coincidence" of P.A.M. Dirac's large-number hypothesis, providing a remarkable linkage between atomic and cosmological parameters. Speaking of things on the atomic scale...
NANOTECHNOLOGY
Nanotechnology is the name coined by K. Eric Drexler in his book "The Engines of Creation". This was actually the area in which I did my Ph.D. research in the mid 1970s, under the less appealing name "Molecular Cybernetics." The idea is to build machines, devices, computers, and sensors on the scale of single large molecules. IBM has already demonstrated a switch whose active component is a single atom, and the Japanese in particular have made nanotechnology a matter of national priority. Nanotechnology can be important to future spacecraft sensors. Today, particle sensors in space primarily measure litle more than the kinetic energy of colliding dust particles. Future nanotechnology devices in space may be deconstructing specks of interstellar dust to understand the exact chemical composition, the revealing distortions of tiny crytslas, the signs of billions of years of the interstellar radiation environment, local cosmochemistry and even to search for pollution from extraterrestrial civilizations. After all, it's very expensive to send big spacecraft across interstellar distances in any time scale shorter than tens of thousands of years. But "spacecraft" the size of grains of sand, or smaller, may be cost effective to send from one solar system to another. So there's another challenge for space sensors: can you build a useful sensor device smaller than a speck of dust, that can operate for centuries of femtowatts of power?
EXTRATERRESTRIALS
Speaking of extraterrestrials, let's get totally into the science fiction mood. Noted Soviet space scientist Kardashev, head of the Radioastron group, has followed up on an idea of the Institute for Advanced Study's Freeman Dyson. Dyson suggests that truly advanced extraterrestrial civilizations may not be intentionally broadcasting radio messages towards us, as we have searched for in SETI projects -- Search for Extraterrestrial Intelligence. But, on the other hand, they may be engaged in building humongous solid constructions far away from any planet. Kardashev announced in the summer of 1991, where my wife and I attended a Planetary Society press conference in Pasadena, that the expected wavelength of waste radiation from such huge artificial objects would be in the far infrared or millimeter wave range. He has begun an international search, lasting at least three years, of the roughly 200,000 infrared objects discovered and mapped by the space shuttle-launched IRAS. We may therefore predict new applications for space sensors, huge infrared and millimeter wave sensors looking in other solar systems for stray radiation from artificial construction projects larger than planets. One must think big to search for artifacts of civilizations more advanced than our own. We are barely on the first rung of Kardashev Type I Civilizations, able to harness energy sources at the scale of a single planet. Type II Civilizations can harness the energy output of a star to build giga-engineering projects such as "Dyson spheres" or Larry Niven's science fictional "Ringworld." Type III Civilizations can harness the energy output of a galaxy, leading to sensor systems such as I proposed in the April 1980 Omni. My wife and I also explored what a Type III Civilization might look like to infrared sensors in our recently completed novella "One Hundred Trillion Planets." What are the implications of what I might term a Type IV Civilization, with energy resources of a galactic cluster or super-cluster? Can we consider that life is evolving towards a Type V Civilization, able to utilize most of the energy in the entire Universe? Perhaps the scientists and engineers should focus on the practical advantages of spacecraft sensors, and let the fiction writers imagine these gigantic possibilities. Or perhaps we should all work together, since the universe is a far stranger place than any single brain can understand.
CONCLUSION
From sensors smaller than specks of dust to alien objects bigger than planets, from Earth orbit to the rings of outer planets, from eyes and ears to artifical noses in space, from the dry CO2 polar caps of Mars to the bottomless oceans beneath the wet ice of Europa, from the electromagnetic spectrum to the exotic neutrinos, gravity waves, gyroscopes on a chip, and tachyons of our most imaginative scientists ... Truly it will take a combination of science fiction visionaries and the kind of expertise we find in the AIAA Technical Committee on Sensors to bring us into the most exciting age of exploration in the history of humankind. Let us begin now to dream, and to use our waking hours to create that golden future. Most importantly, may your checks in the mail be less than a trillion miles away.
*** The End ***
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