This 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.
Electronics and 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 a
Fig. 1 - How the rocket containing a US Satellite
would be launched
(U.S. Navy Photo)
Fig. 2 - Trajectory
of rocket containing US satellite.
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
High-altitude 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 90 minutes.
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.
Fig. 3 - Amateur type setup for tracking
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. 2.
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 off inclination 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 disintegrates.
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.
Tracking the Satellites
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 receiving station.
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.
Each ground 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
Fig. 4 - A miniature U.S. satellite.
(U.S. Navy photo)
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
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.
Fig. 5 - A conventional U.S. satellite in
These specialized 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 accurately.
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 propagation.
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 space.
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 rocket.
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 Fig. 5.)
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 ventures.
Electronics, however, is widely utilized in most of these
studies for recording, filing and storing the wealth of data
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 processing.
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 whole.
March 1958 Radio-Electronics
Wax nostalgic about and learn from the history of early electronics. See articles
published 1929 - 1948. All copyrights hereby acknowledged.
Posted February 27, 2014