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 the
International 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
Model of the scientific earth satellite.
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 line.
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
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 flare radiation.
7. Mercury batteries used as the power source for all instruments.
By Homer E. Newell, Jr.
U. S. Naval Research Laboratory
Electronics in the earth satellite and what we expect to learn from the "laboratory
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.
Even 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.
Vanguard rocket size compared to that of a man.
Artist's concept of the satellite preliminary trajectory.
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
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.
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 effects.
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
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
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 the IGY.
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 IGY satellites.
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
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 Minitrack system.
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
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 output.
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 particles.
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, 1956.
Posted January 6, 2023
(updated from original
post on 7/23/2014)