September 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 acknowledged.
These days, I'm always a bit hesitant to publish or do Internet
research on items mentioning chemical compounds any more toxic than
rubbing alcohol. This article reports on early plans of the Vanguard
satellite launch platform for America's first orbiting satellites.
Although the main focus is on the electronic steering and stabilization
systems, it mentions the fuel composition of
nitric acid and
unsymmetrical dimethylhydrazine. That's probably enough to cause
a federal agent to come knocking on my door... or at least put me
on some sort of surveillance list. Less exotic fuels like
LOX (not to be confused with the fish
used on bagels),
liquid hydrogen, which powered most of the man-carrying booster
stages, would not likely raise a flag.
Precision Steering at 18,000 M.P.H.
Servo Section, Project Vanguard
The Glenn L. Martin Company
The vehicle that will launch the space satellite is right out
of "science fiction", involving as it does the ability to "think"
and cope with the problems of "spacemanship".
At this moment small groups of rocketry specialists in engineering
centers across the United States are pouring the full measure of
their sweat and ingenuity into a project called "Vanguard." Their
assignment is to design and test the rocket vehicle that will launch
man's first satellite.
The date of the first launching is fast approaching. President
Eisenhower has announced that the United States will attempt to
launch several small, unmanned earth-circling satellites during
the International Geophysical Year, July 1, 1957 to December 31,
The project is proceeding under management of the Naval Research
Laboratory, supported by agencies of the Army and Air Force. The
Martin Company of Baltimore is prime contractor, charged with responsibility
for the design and manufacture of the vehicle that will place the
satellite in its orbit. The National Academy of Sciences, through
the Naval Research Laboratory, will provide the satellite itself
and its instrumentation.
"Project Vanguard" has been hailed by scientists as a mission
of great peacetime promise. Artificial satellites are destined to
be man's first observation posts operating for sustained periods
of time beyond the atmosphere. From them will flow an abundance
of new knowledge relating to the earth and the universe.
Yet the day of the satellite would still be a long way off if
it were not for the great strides made recently in rocket propulsion,
structural design, and electronics. A satellite launching system
draws upon these technologies to the limits of their development.
"Project Vanguard" then, a forerunner of future progress, is no
less a sign of present achievement.
The "Vanguard" vehicle is a three-stage rocket powerful enough
to vault through the earth's atmosphere to orbiting altitude of
300 miles. If it did no more, the satellite would immediately fall
back to earth. It must, therefore, be able to accelerate to the
amazing velocity of 18,000 miles-per-hour - the rate that offsets
the centripetal pull of gravity at that altitude, and thereby makes
orbital travel possible. The 11-ton vehicle must have a means, moreover,
of controlling this great lifting strength and velocity so that
the satellite will follow a path that roughly parallels the earth's
Three big demands are thus laid down for the satellite vehicle.
It must lift the satellite to a height of 300 miles; accelerate
it to 18,000 miles-per-hour; and then - at that altitude and velocity
- it must set the satellite free on a path that approximates a tangent
to the earth's surface. That these capabilities may be built into
a single vehicle of manageable size and cost is a tribute to our
state of advancement in rocketry, electronics, and allied fields.
The Three Stages
The second stage of the vehicle, shown at left, contains
a liquid rocket engine, designed and built by Aerojet-General
Corporation. A gimbal mounting system and hydraulic actuation
units similar to those employed in the first stage are used
for control of the thrust vector during the second stage
The composite vehicle, resembling a gigantic rifle shell, is
about 72 feet long and 45 inches at its greatest diameter. The first
two stages are powered by liquid propellants and guided by an inertial
reference system. The third stage, which carries the spherical satellite,
is powered by solid propellant and is maintained in fixed orientation
while it is firing.
The first stage is a liquid propellant rocket similar to the
"Viking" built by Martin for the Navy, but with substantial improvements.
Serving essentially as a guided booster, it develops most of the
energy to raise the remaining stages to orbital height and about
15% of the required orbital velocity. The engine, built by General
Electric Company, delivers a thrust of approximately 27,000 pounds
at sea level. The major propellants, liquid oxygen and kerosene,
are contained in tanks that are integral with the airframe skin.
The rocket motor is fed fuel by turbine-driven pumps. The pressurizing
gas is helium. Control of the vehicle's orientation and flight path
is attained by movements of the engine which is mounted on a gimbal.
In response to autopilot commands, the engine is tilted by electro-hydraulic
actuators to alter the direction of thrust and thus control deviations
in pitch and yaw. Roll control is provided by small auxiliary jet
The second stage of "Vanguard" carries the entire guidance and
control system. In addition it supplies the remaining energy needed
to reach orbital height, and about 30% of the orbital velocity.
It is a liquid propellant rocket that is spliced to the forward
end of the first stage. The propellants, nitric acid and unsymmetrical
dimethylhydrazine, are fed directly to the motor from high pressure
tanks integral with the airframe skin. Again the pressurizing gas
is helium. The motor is gimbal-mounted, as in the first stage, and
positioned in pitch and yaw by electro-hydraulic impulses. An array
of jet reactors provides complete control of orientation during
second-stage coasting flight. Forward of these various mechanisms,
the second stage houses within its nose - which is the nose of the
entire vehicle - the third stage and the satellite.
The plastic nose cone protects the delicate satellite sphere
from the aero-dynamic heating it would encounter if exposed during
the first part of the ascent through the atmosphere. The cone is
jettisoned early in the second stage burning phase, after which
the atmosphere is too thin to be detrimental to the satellite.
The third stage is a solid-propellant, unguided rocket. By approximately
doubling the speed attained by the end of second-stage coasting
flight, it imparts the 18,000 mile-per-hour velocity required for
the satellite to begin its free-flight orbit around the earth. In
the absence of guidance-jettisoned at the time of second stage separation
- this third stage maintains stability by being spun about its longitudinal
axis in the manner of a rifled shell. While still attached to the
second stage, it is mounted on a turntable, or spinning mechanism.
Near the end of second-stage coasting flight, the turntable is set
in motion by small solid propellant rockets. When the third stage
is. spinning, retro-rockets fire-retarding the flight of the second
stage shell. The momentum of the third-stage-satellite combination,
however, remains unchecked. Thus freed, the final rocket begins
its powered flight.
Artist's concept of the satellite preliminary trajectory.
The satellite payload, a 20-inch sphere, is attached to the forward
end of the third stage, and may be separated when orbital velocity
has been attained. As the third stage will reach orbital velocity,
when separated from the payload, it also will become a satellite.
Even at altitudes of 300 miles and above there is a minute drag.
Over a period of time this drag will retard the satellite's velocity
and thus lower its altitude, so that it will describe a decelerating,
descending spiral. When it descends to atmosphere of sufficient
density, the satellite will burn and disintegrate. Based on present
estimates of densities, scientists at the Naval Research Laboratory
calculate that the satellite could exist in a circular orbit of
300 miles height about one year. If the height varies from 200 to
1500 miles at the lowest and highest points (perigee and apogee),
the lifetime would be only 15 days. A 100-mile perigee would end
the satellite's career within an hour.
The preferred orbit - a nominal circle 300 miles above the surface
of the earth - could be attained only if the angle and velocity
of firing were controlled perfectly. Inevitable control errors,
however, will result in an elliptical orbit.
The first stage (portion of complete vehicle shown at
the right) is powered by a liquid rocket engine, employs
liquid oxygen and kerosene as fuels. The thrust cylinder
extends aft of the rocket structure. This cylinder is moved
by hydraulic actuators in a gimbal system so that flight
path control is possible.
It is intended that the initial orbit will lie between 200 and
1500 miles altitude. A greater apogee would hinder optical tracking
while a perigee below 200 miles would seriously reduce the life
span of the man-made moon.
Correct angle of injection depends on correct functioning of
the control system which steers the "Vanguard" vehicle over the
predetermined trajectory. It employs a magnetic amplifier autopilot
working in conjunction with an inertial reference guidance system.
The course is set into the system before launch and played back
via a master sequence controller which initiates each phase of flight
at precisely the right moment. It is thus unlike other guidance
systems that employ radar to track the rocket, issuing steering
commands from the ground with the help of a computer.
All control equipment is located in the electronic section of
the second stage. Heart of the guidance system is a trio of single-axis,
rate-integrating gyros. One is aligned with the "yaw" axis, another
with the "pitch" axis, and the third with the "roll" axis. Once
set and stabilized in a particular plane, the gyros remain fixed
in that plane despite contrary movements of the vehicle. Roll and
yaw orientation are fixed, while the pitch reference is pre-programmed
to establish the curving trajectory planned for the rocket.
Let's say the heading of the vehicle changes from the desired
direction because of a gust of wind, sloshing of fuel in the tanks,
or irregularity of the rocket engine. The deviation is sensed by
the yaw gyro, which remains set on the correct course. The gyro
sends out proportionate electrical signals to the autopilot, which,
operating through electro-hydraulic actuators, causes the rocket
controls to bring the vehicle back on course. Deviations in roll
and pitch are corrected in similar fashion.
is the equipment that will be used to launch the satellite-carrying
Vanguard three-stage vehicle. The structure in the background
is a gantry crane used to erect and assemble the vehicle
and to provide work platforms from which the field crew
can test the rocket prior to launch. At the lower right
is the concrete blockhouse from which the rocket operation
is monitored prior to and during flight. All final tests
are remotely performed by personnel locked in the blockhouse
and when the rocket is ready for flight it is fired from
this remote location. As seen in this sketch, the Vanguard
launch stand does not include a pit to conduct exhaust gases
away from the rocket but rather the vehicle itself will
be elevated and steel exhaust duct provided. The rocket
will be finless and stabilization will be achieved by use
of a gimbaled engine. Omission of fins saves weight.
The phase lead required to stabilize the rocket is produced by
operational networks that introduce a phase lag in the feedback
circuit of the amplifiers.
Using the conventional equations for a feedback amplifier:
where: Kƒ=gain with feedback
K = forward gain
where: Kb is a function of the number of turns on
the feedback winding and the values of the resistances.
On substitution we obtain: 1 + (RCS/2)
When compared with a conventional lead circuit, this equation
shows that the time constant, T, is given by (RCS/2) and the attenuation
by 1 + KKb.
The all-important velocity of the "Vanguard" vehicle is measured
by an integrating accelerometer installed in the second stage electronics
section. The instrument senses the acceleration applied to the vehicle
during flight, sums it up, and thus yields the velocity. The velocity
measurement made at the end of the burning of the second stage is
supplied to the unit's analogue computer, which determines how long
the vehicle will coast before the third stage, carrying the satellite,
The basic component is a floated gyro. An acceleration on its
sensitive axis generates a signal which, when amplified, drives
a turntable which rotates the gyro about its input axis. The resulting
torque is equal and opposite· to the acceleration torque. Since
the turntable turns at a rate proportional to acceleration, its
position is proportional to the integral of acceleration, or velocity.
The relation between torque and input, angular velocity depends
on the angular momentum which, in turn, depends on the power frequency.
There is no means of compensating for changes in frequency. Consequently,
since the frequency of the 400 cps supply is not controlled accurately
enough, it is necessary to generate an accurate 400 cps. This is
done by means of a tuning fork whose output is amplified in a transistor
amplifier to drive the gyro.
Posted August 26, 2014