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.

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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 ***