May 1957 Radio & TV News
Wax nostalgic about and learn from the history of early
electronics. See articles from
Radio & Television News, published 1919-1959. All copyrights hereby
Atmospheric scientists suspected as recently as early 1957 that
Earth's upper atmosphere (ionosphere and
beyond) temperature might be around 1,000° K. I
say 'suspected' because we had not yet launched instruments there
to make actual measurements. Soundly posited and agreed upon theory
was validated a short time later when sounding rockets reliably
reported a maximum of about 1,300° K in the upper ionosphere.
We did not know for sure what electromagnetic wavelengths and their
respective energy densities would be outside the protective layers
of gases encompassing Earth. Much more was known about the depths
of the planet's oceans than of its atmosphere. Scientists knew that
life was abundant below the water's surface but did not know what,
if any, life existed at altitudes any greater than the tallest mountain.
Outer space, devoid of everything we consider essential to support
life as we know it, would be a hostile environment for humans or
even electronic instrumentation. It is always interesting to recall
that while you only need to dive 33 feet below the water's surface
to double the ambient pressure, you need to go 18,000 into the atmosphere
to halve the pressure. Beginning in 1957, a consortium of more than
60 countries banded together to discover as much as possible about
outer space by building instrumentation and launch vehicles during
Geophysical Year (IGY, which actually lasted for around 18 months).
Science magazines like Radio & TV News spilled a lot
of ink onto their monthly pages to keep the public apprised of data
being collected. The results are inarguably responsible for the
occupation and exploitation of space-based communications and observation
systems that rapidly ensued.
Research at the Threshold of Space
By Homer E. Newell, Jr.
U. S. Naval Research Laboratory
The instruments indicated by the lettering and numbers
on the satellite are:
A. Solar cell. peak memory reset. Solar cell operating
on energy from sun will reset peak memory storage unit once
each orbit on transition from darkness to daylight.
B. Ion chamber, narrow band for ultraviolet detector.
Peak ultraviolet sensitivity at the hydrogen Lyman-alpha
C. Thermistors, semiconductors made of various metal
alloys, used for temperature measurement. The resistance
changes with temperature.
D. Erosion gauge, nichrome ribbon evaporated on glass.
Measures surface erosion caused by impact of micrometeorites.
Resistance increases as film becomes pitted.
1. Minitrack transmitter. Supplies r.f. link for continuously
telemetering the data from the satellite to ground. Operating
life about 2 weeks with batteries.
2. Meteor storage, meteorite collision memory. Magnetic
cores are used to store the number of "counts" from the
meteoritic collision detector and transmit signals representing
four decimal digits on four telemetering channels.
3. Telemetry coding system. Successively samples various
signal input channels and appropriately modulates the Minitrack
radio tracking transmitter for transmitting scientific data
to a ground recording station.
4. Lyman-alpha storage, peak memory unit. Magnetic cores
are used to store and code the telemetering system with
a signal representing the maximum input value reached during
one satellite orbit for subsequent readout when passing
over recording stations.
5. Meteoritic collision amplifier. Amplifier output signal
from a sensitive microphone is used to detect any collision
that may occur with micrometeorites and provides input to
the meteoritic storage counter.
6. Lyman-alpha unit. Current amplifier for measuring
the amount of ionization produced by far ultraviolet solar
7. Mercury batteries used as the power source for all
Model of the scientific earth satellite described to the left.
Electronics in the earth satellite and what we expect to
learn from the "laboratory in space."
Dwelling at the surface of the earth man moves about in what
has often been called an "ocean of air." If all of the air in the
atmosphere were at sea level temperature and pressure, this ocean
of air would be about five miles thick. In fact, however, the atmosphere
rises some hundreds of miles to merge at some unknown level with
almost, but not quite, empty space. Below about 60 miles, atmospheric
temperature varies with height between warm and very cold, but at
higher altitudes gets very hot, probably more than 1000 K (Kelvin
scale-degrees = degrees C + 273.1 above 150 miles. At the same time
the pressure and density fall off exponentially with height, so
that at 60 miles the air is only one-millionth as dense as at sea
level, and at 200 miles is probably only 10-11 as dense
as at the ground.
At some altitude above 200 miles the mean free path of the air
molecules becomes so great that any molecule speeding vertically
at more than the escape velocity will depart from the atmosphere
into interplanetary space without colliding with any other air molecule.
This height marks the beginning of what is often called the "exosphere,"
and may be termed the threshold to space.
Since the dawn of history, and earlier, man has looked out through
the atmosphere at the sun, the moon, the planets, and the stars.
The science of astronomy and astrophysics is based on observations
made through this window of air, which at first thought may seem
to be perfectly transparent. The fact of the matter is, however,
that this window of air is transparent only in certain restricted
regions of the wavelength spectrum. The visible wavelengths, parts
of the infrared, and parts of the radio-frequency spectrum penetrate
the atmosphere to reach the ground, but the remainder is cut off
completely. For example, none of the solar or stellar radiation
below about 2900 A (angstrom unit =10-8cm) ever reaches
the surface of the earth. The astrophysicist is, therefore, prevented
from observing the sun or the galaxy in regions of the spectrum
that could be highly revealing.
in the regions in which it is transparent the atmosphere imposes
some restrictions. Because of turbulence and dust, the ultimate
accuracies to which the astronomer can attain are limited quite
severely, considering the present state of the art.
Geophysicists have studied the upper atmosphere and events occurring
in it for over half a century now. Pressure, temperature, density,
winds, the aurora, airglow, the ionosphere, meteors, cosmic rays,
air composition, the earth's magnetic field, all have come under
this scrutiny. During most of this period, all of the observations
were made from the ground or near the ground. For a long time the
highest altitudes attainable were those reached by balloons. As
a result many of the conclusions about the high atmosphere were
obtained in a highly indirect fashion. Often the theory connecting
the observational fact with the ultimate object of study was highly
involved and open to considerable doubt. In this respect the sounding
rocket has been of great value to the geophysicist. During the past
ten years it has been possible in such rocket vehicles to place
measuring instruments in direct contact with the upper atmosphere.
These rocket measurements have given the geophysicist the data needed
to correct many of the theories used in interpreting ground based
observations. Moreover, they have provided data unobtainable otherwise:
ultraviolet and x-ray radiations from the sun; levels of ionospheric
currents; high altitude values of the earth's magnetic field; chemical
and ion composition of the air; auroral particles; very low energy
and highly ionizing cosmic rays; and micrometeorite counts.
During his study of the earth's atmosphere the geophysicist has
had a growing interest in things beyond the atmosphere. The sun,
of course, is important because it is the single greatest source
of energy input into the atmosphere. The auroras are now believed
to be caused by charged particles entering the atmosphere from interplanetary
space, originating in the sun. It is also thought that magnetic
storms are associated with electric currents existing far beyond
the earth's atmosphere. Meteors and micrometeorites come from interplanetary
space. Whereas some cosmic rays may come from the sun, many of them
probably arrive from galactic and intergalactic space.
Thus the astronomer, the astrophysicist, and the geophysicist
all have a great interest in looking into outer space without having
to look through the atmosphere. The astronomer would like to place
his instruments above the air where seeing would be unimpaired.
The astrophysicist would like to study the sun and stars from above
the atmosphere so that he can observe them in important wavelengths
that do not penetrate to the ground. Finally, the geophysicist would
like to observe those solar and particle radiations and other phenomena
which affect the atmosphere, the earth, or its magnetic field.
Artist's concept of the satellite preliminary trajectory.
The vertical sounding rocket can be used to a limited extent
for such observations. Its principal value, however, is for studying
events occurring within the atmosphere, particularly for making
measurements as a function of altitude at essentially a single instant
of time. The glimpse that it can afford of conditions above the
atmosphere and in outer space comes only near the peak of flight,
and is brief, whereas most of the desired observations at or above
the threshold to space become of real value only when carried out
over extended periods of time. Examples are: monitoring the ultraviolet
light from the sun over sufficient time that the data can be correlated
with weather effects; and monitoring flare activity in the sun so
that it can be correlated with ionospheric, magnetic, and auroral
An observing platform at the threshold to outer space would meet
the needs of astronomer, astrophysicist, and geophysicist alike.
But one cannot just place such a platform at some point in space
and expect it to stay there. Even if it were motionless to begin
with, the gravitational attractions of the sun, the earth, the moon,
and the planets would cause it to move. If it were much closer to
the earth than to any of the other bodies in the solar system, it
would simply fall to the ground. If it were far removed from any
of the planets, the sun would be the controlling factor, and the
platform would fall into the sun. The conclusion is that such an
observing platform will necessarily be in motion, and the problem
is to find some motion which does not destroy the usefulness of
the platform for making observations.
The moon is obviously a highly acceptable platform for making
physical observations outside the earth's atmosphere. In revolving
about the earth the moon stays well outside the earth's atmosphere,
and since it has no atmosphere of its own, it would be an ideal
spot to locate telescopes, spectrographs, light and particle counters,
etc. There is, however, some difficulty associated with setting
up operations on the moon. One is led, therefore, to the idea of
creating an artificial moon revolving close to the earth, carrying
automatic equipment for collecting data, and a radio transmitter
for sending the data to the ground. This can be accomplished using
suitably designed rockets.
International Geophysical Year
The idea of creating an artificial satellite of the earth is
far from new. For many decades rocket engineers have had such a
thought in the back of their minds. Many enthusiasts have regarded
the creation of a space platform as a principal objective of rocket
development. The immediate motivation for the current United States
artificial earth satellite program is to be found, however, in the
International Geophysical Year.
From the beginning of July, 1957 to the end of December, 1958
about 50 nations will unite in an attack upon various important
geophysical and solar problems. The participation of the United
States in this program is under the direction of the United States
National Committee (USNC) for the IGY, established by the National
Academy of Sciences. Their observations will be made in a coordinated
fashion from stations covering the entire globe. It is expected
that these coordinated and correlated observations will lead to
a number of major breakthroughs in such fields as meteorology, ionospheric
physics, aurora and airglow, solar activity, cosmic rays, geomagnetism,
latitude and longitude, oceanography, glaciology, gravity, and seismology.
In addition to scientific value, such breakthroughs could be of
great practical importance, possibly leading to better weather forecasting,
improved radio communications, better navigation, and more effective
means of mineral prospecting.
A large part of the International Geophysical Year effort will
be devoted to a study of the upper atmosphere and the sun. To this
end the United States National Committee (USNC) for the IGY has
generated rocket and satellite programs. The former program is managed
by a Technical Panel on Rocketry, created by USNC, and involves
the firing of some 200 vertical sounding rockets during the IGY.
The latter program is managed by a Technical Panel on the Earth
Satellite Program (TPESP), also established by USNC, and involves
the launching of a small number of instrumented satellites during
Diagram showing the distribution of ultraviolet radiation
and layers of ionosphere with respect to the satellite position.
In the management of the scientific aspects of the satellite
program, the TPESP has set up two working groups, one on tracking
and computation (WGTC) and one on the internal instrumentation of
the satellite (WGII). The WGTC acts as adviser to the TPESP on such
things as optical and radio tracking of the satellite, on the reduction
of tracking data and the computation of an orbit and ephemerides
for the artificial moon, also on the use of such data for geodetic
studies and for determining the density of the upper atmosphere.
The WGII advises on experiments requiring operating instruments
in the satellite. This working group has received almost three dozen
proposals from various research agencies for experiments to be done
in IGY satellites. The WGII is studying these proposals to assess
their scientific importance, their appropriateness to IGY, their
feasibility in a satellite, and whether or not they are best done
in a satellite. Out of these studies there is developing a sort
of priority listing of the proposed experiments, and eventually
the TPESP will select those experiments actually to be flown in
Instrumentation for Satellite
The Launching Operations: The IGY satellites will be launched
from Cape Canaveral by means of a finless three-stage rocket. Rising
vertically at first, the rocket will start tipping shortly after
take-off, moving a little to the south of east in a trajectory that
will ultimately lead to projecting the satellite into an orbit inclined
at about 35° to the equator. The first stage will be discarded
at the end of its burnout, and the second stage will then carry
the third stage rocket with the 20-inch, 21.5-pound satellite attached
to its nose up to 300 miles altitude about 700 miles from the take-off
point. By the time the second stage with cargo has reached its peak
altitude it will have been tipped over to the horizontal, thus aiming
the third stage solid-propellant rocket along its intended orbit.
At this time the third stage will be spun to provide stability,
separated from the second stage, and fired. Following burnout of
the third stage the satellite package itself may or may not be separated
from the empty rocket depending on the requirements of the experiments
being performed. If the satellite and the third stage rocket are
separated, this will, in effect, result in two satellites, since
the empty rocket casing will also continue to revolve around the
earth in an orbit of its own.
During these launching operations, it will be necessary to monitor
the vehicle and its equipment. This will be done both by tracking
and by telemetering. For the tracking, ballistic cameras and theodolite
systems, radar, and the Minitrack system to be described later will
be used. Telemetering will be accomplished by means of what have
now become conventional techniques, using various combinations of
frequency, pulse-position, and amplitude modulation. Especially
during the program of test firings prior to the first actual attempt
to create a satellite there will be a need for extensive telemetering.
Optical Tracking of the Satellite: It is planned to make the
first satellite in the form of a highly polished, silvery sphere,
20 inches in diameter. If the launching goes as planned, the orbit
of the satellite will lie entirely above 200 miles altitude but
may extend out as far as 1500 miles. At the nearer altitude, such
a satellite should be just barely visible to the naked eye if present
in the neighborhood of the observer within about an hour after sunset
or before sunrise. With ordinary binoculars, on the other hand,
the sphere should be quite easily visible, and at the request of
the TPESP, the Smithsonian Astrophysical Observatory (SAO) is organizing
an amateur program of looking for the satellite. In this program,
called "Moonwatch," the observers will use binoculars. At each station
a large number of binoculars will be set up so that their fields
of view overlap forming an observational fan crossing the sky from
north to south. Suitable timing will be provided so that the time
as well as position of passage across the fan can be determined.
This program of visual observing is also being extended internationally
so that there will be stations located all around the world throughout
the belt over which the satellite is expected to pass.
Artist's conception of the three-stage launching rocket
that will place the scientific satellite in its orbit. Vehicle
will resemble giant 30-callber rifle shell.
The primary purpose of the visual program, however, is to acquire
the satellite and to get a rough estimate of its orbit. Precision
tracking, to provide data for use in geodetic and air density studies,
will be carried out using specially designed Schmidt cameras. These
instruments, with 20-inch aperture and 20-inch focal length, will
be able to photograph the satellite against the star field, even
at the 1500-mile distance, positioning the satellite to within seconds
of arc and a millisecond of time. These photographic stations are
also being set up by SAO, and will be spread around the world in
the expected orbital belt. About a dozen such stations are presently
Radio Tracking of the Satellite: Optical observation of the satellite
depends on a number of factors not under the control of the observer.
As mentioned the sphere can be observed only at certain favorable
times, so that any given station will be able to sight the satellite
infrequently. The chance of such an optical sighting will be further
reduced by poor weather.
Radio tracking can be achieved night or day, independently of
weather. Moreover, a single antenna beam can be made to cross the
sky from horizon to horizon. With a group of such beams running
across the entire orbital belt a sort of radio picket fence can
be established to contact the satellite each time it crosses the
fence. This is what is to be done with the Naval Research Laboratory
The Minitrack system uses radio interferometry. A continuously
operating transmitter in the satellite will send a 108.0 mc. c.w.
signal. This signal will be received at two antennas on the ground
separated large number of wavelengths and compared in phase. The
phase difference can then be used to determine one direction angle
to the satellite. Two sets of such antennas at right angles to each
other will be to us give the two angles needed to fix the direction
from the ground station to the satellite. The radio fence planned
will include stations running from Washington, D. C. to Santiago,
Chile, a station in Antigua, British West Indies, and one at San
Diego, California. This fence, including 11 stations in all, will
provide on the order of 20 sets of observations per day. In the
initial stages it is estimated that this data should suffice to
determine the satellite's orbit to within a minute so of arc and
a millisecond of time. After a couple weeks of observing, the data
should be adequate to give the orbit to within about a third of
a minute of arc, which is not as accurate as the photographic results,
but nevertheless approaches precision quality.
Using transistor circuitry a Minitrack transmitter has been constructed
that weighs only a couple of pounds including the batteries for
several weeks of continuous operation at from 25 to 50 milliwatts
Telemetering: The optical observations of the satellite do not
require any equipment in the satellite, although a light source
in the orbiting vehicle would be of assistance. Satellite-borne
equipment is required, however, to send back the information obtained
by instruments in the sphere. For the IGY satellite. this radio
telemetering will be accomplished by means of the Minitrack transmitter.
The data obtained by the various sensing elements will be coded
by a suitable premodulator into a waveform suitable for modulating
the Minitrack carrier, and then impressed on the tracking signal.
The percentage modulation of the carrier will be limited so as to
maintain the integrity of the tracking during the telemetering operations.
In some cases the telemetering may be carried on continuously along
with the tracking. In others, a command signal from the ground may
be used to turn on the satellite-borne scientific instruments for
a limited time, simultaneous switching from the low-powered tracking
oscillator to a higher powered tracking-telemetering oscillator.
The premodulator to be used should be designed as a more or less
integral part of the experiment to be performed in order to save
space and weight. The particular approach to be used will be dictated
by the experimental requirements. The University of Iowa has, for
example, signed a lightweight magnetic tape recorder into an experimental
setup for cosmic ray observations from a satellite. Using this,
data can be stored throughout the entire satellite orbit and then
read out as the satellite passes over an observing station. The
Naval Research Laboratory has designed an extremely lightweight
unit using magnetic cores and transistors. This premodulator provides
48 channels of information, comprising a total bandwidth of 10 kc.,
handles a wide variety of inputs, and with batteries for 3 weeks
of operation weighs only a little over half a pound.
Possible Satellite Instruments: For the IGY satellites, there
are numerous experiments of genuine interest and importance. Only
those, however, that can be performed with equipment weighing no
more than a few pounds can be carried out. With this stringent weight
requirement in mind, let us then consider existing instrumentation
that might form the basis for an IGY satellite experiment.
Temperatures on the surface of the satellite or in its interior
might be measured with thermistors or similar gauges. These together
with the necessary circuitry are extremely light, totaling only
ounces. Likewise there are very light hot wire, ionization, and
mechanical pressure gauges that could be used to measure pressures
within certain regions in the satellite. This could be a means of
checking on whether or not the satellite experiences a serious puncture
by a meteor.
There are lightweight microphones, which together with their
circuitry weigh on the order of an ounce. These could be used to
listen for the impact of meteors against the satellite surface.
Very thin metallic coatings could be used as resistance elements
in an electrical circuit and placed on the outer surface of the
satellite. If these were to wear away because of encounters with
particles in space, their resistance would increase. By measuring
the change in resistance the rate of erosion could be determined.
Very lightweight geiger counter circuits can be made for the
observation of cosmic rays. Such counters and ionization chambers,
seem to be a natural choice for measuring these extremely high energy
Photon counters and ionization chambers can also be used for
observing the sun's radiation. For example, a satellite installation
has been developed at the Naval Research Laboratory for monitoring
the sun in the Lyman-alpha region of the spectrum. This equipment
uses an ionization chamber for the primary measurement and a solar
cell for aspect determination. With the power supply for two weeks
of operation it weighs only a couple of pounds.
Packard, of the Varian Associates, has studied the problem of
constructing a nuclear resonance magnetometer for use in a satellite.
He has concluded that such an installation can be made weighing
a total of four pounds, including the power supply for about three
weeks of operation. In this type of magnetometer, a proton rich
substance, like water, is placed inside a coil of wire. The coil
is energized for a short time with a strong current, causing the
magnetic moments of the protons to align themselves with the coil
field. The coil is then de-energized, after which the protons begin
to precess around the direction of the earth's magnetic field. The
precession gives rises to an alternating e.m.f. in the coil containing
the water, which signal can be amplified and recorded. It so happens
that the frequency of this signal depends on the strength of the
earth's magnetic field, but not on its direction. By suitable calibration,
then, the device can be used to determine the strength of the magnetic
field in which it is embedded. The weights quoted by Packard make
it practical to consider this instrument for use in an IGY satellite.
Photocells can be built into a sufficiently lightweight installation
for satellite use. Such an installation might be used for measuring
the albedo of the earth, or to look for cloud cover on the earth.
The radio transmitter may be looked upon as a means of obtaining
scientific data. The Minitrack signal at 108 mc. will be affected
by the ionosphere. The frequency was chosen so that this effect
will be too slight to affect the tracking seriously. It will however,
be detectable, and should furnish a measure of the total ionization
in the ionosphere.
Finally. solar cells can eventually be used in power supplies
for artificial satellite experiments. The Signal Corps Engineering
Laboratories at Ft. Monmouth, New Jersey, have already worked up
a solar supply that comes within the weight limitations of the IGY
satellites. This device will undergo a series of tests in the near
future. It may be that the necessary engineering can be accomplished
soon enough to work such a solar power supply into some of the IGY
satellites. If so, the total period of operation may be extended
from the weeks expected with conventional batteries to an appreciable
fraction of a year.
The reader who wishes to pursue these thoughts further may be
interested in consulting a new book: "The Scientific Uses of Earth
Satellites," edited by James A. Van Allen, and published by the
University of Michigan Press. The book contains papers presented
at a symposium held at the University of Michigan during January,
Posted July 23, 2014