second in a series of International Geophysical Year (IGY) articles
that appeared in Radio-Electronics magazine. The author covers
basics of satellite configuration, launching, and tracking based on
knowledge of the era. Keep in mind, though, that the U.S. had not actually
launched its first satellite at the time. In fact, the two satellite
models shown possess antennas suggesting active radio circuits within,
but Echo, our first earth-orbiting satellite, was just a metallized
plastic sphere that passively reflected radio signals. The Russian Sputnik,
by comparison, did have electronic circuitry onboard.
March 1958 Radio-Electronics
of Contents]These articles are scanned and OCRed from old editions of the Radio & Television News magazine.
Here is a list of the Radio-Electronics articles I have already
posted. All copyrights (if any)
are hereby acknowledged.
See all available
vintage Radio-Electronics articles.
the IGY - Part II
Part II: - What part will earth satellites play in the International
By Jordan McQuay
In the search for scientific data during the IGY no single activity
has stirred the imagination and interest of the world more than the
earth satellites - the rocket-borne metal spheres sent into outer space
to circle the earth, whirling free through an orbit in upper atmosphere.
Long considered a theoretical possibility, it was not until recent development
of rockets and missiles of tremendous size that this dream has become
Fig. 1 - How the rocket containing a US Satellite would be launched
(U.S. Navy Photo)
Fig. 2 - Trajectory of rocket containing
In October, 1957, the first satellites were launched
by Russia. A series of satellites will be launched by the United States
during the late winter and spring of 1958.
Weighing about 185
pounds and about 2 feet in diameter, the Russian type of satellite is
launched into space by multiple-stage rockets of tremendous size and
thrust. Once it overcomes the gravitational pull of the earth at an
altitude of several hundred miles, the satellite circles the globe in
an orbit 200-400 miles above the earth at about 18,000 miles an hour.
Altitude gradually drops over a period of several weeks or months, and
the satellite eventually disintegrates due to air friction.
Although technical details of the Russian satellite have not been revealed,
it contains a radio transmitter which broadcasts a coded signal (on
20 and 40 mc). Since it is powered by some sort of miniature storage
battery, failure of the power supply after 4 or 5 weeks means the satellite
moves silently through its orbit until it disintegrates. General theory
behind the Russian satellite, however, is much the same as that of the
several types of satellites soon to be launched by the United States.
rockets, described last month, provided the first direct experimental
observations of the upper atmosphere. These included data on air pressure,
density, temperature, composition, wind fields, cosmic rays and other
solar activities. A major limitation of these rockets is the brief period
of time during which the measurements could be taken - usually for only
6 or 7 minutes. Rocket coverage is also restricted to a small part of
the earth's atmosphere.
An artificial satellite, propelled into
space and whirling in an orbit far above the earth, will provide weeks,
months, even years of continuous, reliable data for scientific study.
Also, the satellite traverses a vast amount of interplanetary space
during each revolution around the earth and thus collects a great amount
of geophysical information.
Once in its orbit, the satellite's
velocity is such that its centrifugal force balances the earth's gravitational
pull. Without additional propelling power, the satellite continues to
circle the earth, making a complete revolution about once every 80 or
The principal problem is launching the satellite
and propelling it upward into its orbit. This is done by transporting
the satellite in the nose of a multistage rocket which has sufficient
power to carry the satellite into the upper atmosphere.
The United States uses a three-stage rocket (Fig. 1). It is 72 feet
long and is launched vertically. Finless, it uses internal electronic
controls for guidance. The trajectory of the rocket is shown in Fig.
Fig. 3 - Amateur type setup for tracking earth satellites.
When fired, the first stage of the rocket thrusts the entire
assembly upward almost vertically. It then tilts slightly until, at
burnout, the rocket is inclined at about 35°. Then, its fuel exhausted,
the first stage detaches itself from the rocket assembly. The second
stage then drives the rocket to an altitude of about 140 miles, propelling
it at a rapidly increasing speed to about 2,000 miles an hour, and -
through electronic controls - diminishes the angle
to only a few degrees. As the rocket levels off and coasts for some
distance, the second stage detaches itself and ignites the third and
final stage of the rocket. The third stage carries the satellite to
its ultimate altitude of several hundred miles and to its top speed
of about 20,000 miles an hour. The satellite separates from the third
stage and, established in its orbit, continues under its own momentum
- about 1,500 miles from the launching site and about 10 minutes after
launching. Because of its extreme speed at time of separation, the third
stage may continue to orbit somewhere in space behind the satellite.
After some time, however, the third stage will drop in altitude until
it disintegrates in more dense atmosphere.
Although a satellite
may continue to circle the earth for protracted periods of time - several
weeks, months or longer - ultimately atmospheric drag will bring its
orbit closer and closer to the earth. When it enters the denser atmosphere
of lower altitudes, the satellite (due to air friction) will burn out
far above the earth's surface. Both it and burned-out stages of the
rocket will drift to earth as indistinguishable dust and ashes.
While in flight, the tiny satellite broadcasts a periodic signal
giving the specific data it measures - such as air density, pressure,
temperature .or solar activities. The radio transmitter in each US satellite
weighs about 13 ounces and has a 10-mw output at a fixed frequency of
108 mc. It is crystal-controlled and completely transistorized. Some
types of satellites may have transmitters powered by seven 1.2-volt
miniature batteries. Others will be powered by solar batteries, which
give the transmitter a continuous life until the satellite eventually
The type of data transmitted by a satellite depends
upon the instruments contained within its spherical metal shell. Measurements
are fed to electronic telemetering equipment, which translates them
into coded signals. Then the radio transmitter broadcasts these signals
to ground tracking and observing stations.
Once established in its orbit, a satellite
must be tracked - both optically and electronically - to provide position
and path information to correlate with other readings and measurements.
With previous knowledge of the probable path of a satellite gained through
electronics, observers at ground stations can use photo-theodolites
for optical tracking. This method of tracking, however, depends upon
fair visibility for good accuracy.
A more reliable method of
tracking is the Minitrack system, which utilizes radio receiving equipment.
The radio transmitter within the satellite produces a periodic signal
at 108 mc, which is radiated by small antennas outside the metal sphere.
On the ground, the signal can be detected by highly sensitive receiving
equipment whenever the satellite passes in the general vicinity of a
Orbits of all US satellites are expected
to have a latitude range of about 35° above and below the equator.
Within this broad belt, Minitrack stations have been erected by many
governments at strategic points around the world. Although development
and launching of the US satellite is primarily a contribution of this
country to the IGY, all countries are participating in observing and
measuring data obtained by each of the US satellites.
station of the Minitrack system is equipped with several sets of two
specially designed and highly balanced receiving antennas, a frequency
converter, a high-gain amplifier and a visual recording device. When
tuned to the 108-mc frequency and with the satellite within receiving
range, there will be an indication on the output recording device -
the amount depending on the proximity of the satellite to the station.
The satellite can be located in its orbit by comparing the signal from
one antenna with the signal from the second antenna of each set. This
is equivalent to comparing the path length of the signal from the satellite
transmitter to one receiving antenna with the path length of the signal
to the second antenna of each set of matched antennas. Similar measurements
with other sets of matched antennas at the receiving station will fix
the satellite even more accurately.
A simplified version of
the Minitrack system can be used by radio amateurs residing in the region
to be covered by each US satellite. As shown in Fig. 3, as few as two
balanced antennas are connected via a frequency converter, to the input
of a conventional communications receiver. An S-meter or other visual
indicating device is used at the receiver's output. As the satellite
passes over the vicinity of the station, the receiver output varies
from a minimum to a peak. The maximum reading determines the general
position of the satellite. It recurs about every 90 minutes.
The equipment at each Minitrack station is considerably more complex
and provides a high degree of precision measurement. In addition, the
satellite signal is continuously recorded at each Minitrack station.
In event of failure of the satellite's radio transmitter, ground-based
radar equipment tracks the satellite.
All tracking information
is transmitted to key or central stations. There, using instantly available
data from all reporting sources, electronic computers calculate orbital
information and predict the exact path of any satellite for each successive
revolution. This prediction includes the time and place of meridian
passage, the zenith angle and the angular velocity of a satellite in
its orbit. With each successive revolution, these data are reevaluated
and recomputed, and new predictions are made by electronic data processing
and computing equipment.
Data from the Satellites
Fig. 4 - A miniature U.S. satellite.
(U.S. Navy photo)
Fig. 5 - A conventional U.S. satellite in space.
As each satellite
travels through space, specialized types of scientific data are also
obtained and measured by instruments within the sphere and then transmitted
to ground stations for collation and record.
data may relate to the sun's ultraviolet rays, meteor particles, air
density, cosmic rays, the ionosphere or any of many other fields of
scientific endeavor during the IGY. The type of data obtained and telemetered
to earth by each satellite depends entirely upon the type of instruments
within the satellite. The instrumentation is usually different for each
of the US satellites, depending upon its mission. By nature of their
movement in space, however, all satellites provide important scientific
data concerning air density, the shape of the earth, the ionosphere
and other scientific fields.
Since the orbit of a satellite
is influenced by local non uniformities in the gravitational field,
observations of the orbit at ground tracking stations make possible
calculations of mass distribution of the earth. This, in turn, yields
information about the composition of the earth's crust. Similar information,
after electronic analysis, also provides data about the oblateness or
flatness of the earth near the poles. Orbit observations also make possible
precise determinations of latitude and longitude, particularly for isolated
islands, many of which in the Pacific have never been located and mapped
Since radio signals from a satellite are affected
as they pass through the ionosphere, this phenomenon permits measurement
of refraction as well a other characteristics of the ionosphere. Such
measurements are important to the study and prediction of radio-wave
All types of data collected and recorded during
the IGY - by Minitrack, optical and other tracking stations as well
as scientific observing stations - are transmitted to key or central
stations. There the various data are fed to electronic data processing
equipment for immediate or future reference.
From this mass
of accumulated and correlated information, detailed an accurate scientific
data can be compiled electronically and almost instantly months, even
years, after a satellite has completed its flight through interplanetary
During this winter and spring, the United States will
launch four miniature satellites. These are trial flights primarily
to test the Minitrack and rocket-launching systems. Each of the test
satellites is about 6 inches in diameter - the size of a grapefruit.
Each has six protruding antennas and contains a tiny radio transmitter
powered by solar batteries to convert energy from the sun into electricity.
(See Fig. 4.) Each will be launched by a conventional high-power three-stage
Larger satellites, to be launched during this summer,
will be equipped to obtain specialized scientific data. These are about
20 inches in diameter and weigh 21 pounds. Each is equipped with a transmitter
and has four protruding antennas to radiate data to the ground. (See
The first of the large satellites will carry instruments
to study the sun's ultraviolet rays and obtain environmental data. Succeeding
satellites will record erosion of meteor particles in space, measure
air density and composition, the earth's magnetic field, cosmic rays,
and obtain other scientific data.
There are numerous other studies of scientific significance
during the IGY. Simultaneous studies in oceanography and glaciology
are exploring the heat and water interrelationships that also affect
the earth's weather and climate. A study of seismology leads to new
knowledge of the earth's core and crust. Gravity measurements and related
studies are also part of the activities of all participating countries.
But electronics assists to only a very small degree in these international
Electronics, however, is widely utilized in most of
these studies for recording, filing and storing the wealth of data obtained.
At key control centers throughout the world, the latest types
of electronic data-processing equipment handle, record and store the
vast amount of data collected continuously during the IGY. Electronic
computers are utilized for fast computation and analysis. Data is recorded
on punched cards or on metallic tape, then filed in electronic storage
memories for future reference. This makes the handling of billions of
items of measurement and observation largely automatic - through electronic
The IGY is destined to yield unprecedented knowledge
about the mysteries of the earth and the atmosphere and their relationship
to the sun. In geophysics, the universe itself performs the experiments
in which mankind is interested. The events that determine our physical
environment are therefore worldwide in nature, and only through the
cooperative efforts of all countries can their secrets be discovered.
Thus, through the joint effort of many nations, the International
Geophysical Year is not only an expression of the scientific interests
of various countries, but the scientific community of the world as a
Posted February 27, 2014