|
March 1967 Electronics World
 Table
of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
|
We take for granted most of the technology that surrounds us.
Unless you were alive 50 years ago at the dawn of microelectronics
and space flight, it would be difficult to imagine a world without
cellphones, desktop computers, color TVs, the Internet, and
even satellite-base weather forecasting. Everyone likes to make
jokes about weathermen being no better at predicting the weather
than your grandmother's roomatiz[sic], but the fact is that,
especially for short-term (2-3 days) predictions, we get pretty
good information. As a model airplane flyer, I check the wind
level forecast nearly every day to see whether my plane can
handle it. AccuWeather's free hourly forecast is usually pretty
darn accurate for today's and tomorrow's wind - to within a
couple MPH. A plethora of ground reporting stations help improve
accuracy, but data streamed from spaceborne instruments are
the real key. This story in the 1967 Electronics World reports
on some of the earlier imaging weather satellites. Amusingly,
it also predicts the possibility of someday controlling world
weather with the satellites' assistance.
Weather Surveillance by Satellite
By Joseph H. Wujek, Jr.
Tiros, Nimbus, and successor ESSA satellites are providing
global weather information that may one day lead to global weather
control.
The new "cartwheel" Tiros photographs the
earth as the satellite rolls along like a wheel in a near-polar
orbit.
To a great extent, man has learned to use the forces of nature
beneficially. A notable exception is our inability to control
those forces in nature which we know collectively as weather.
Weather plays an important part in social and economic well-being
of a nation. Agricultural output is strongly tied to the weather,
as is the movement of ships at sea, aircraft, and land transport.
Indeed, commerce as a whole depends to some degree on the behavior
of the elements. In war as in peace, a nation's fate may be
decided by the perversities of the weather. The defeat of the
Spanish Armada, as well as the defeat of Napoleon's armies on
the plains of Russia, were due in large measure to severe weather
conditions.
In view of all this, it is not surprising that meteorologists
continually searching for new tools to aid them in understanding
the weather. With increased knowledge of weather comes the ability
to predict the kind of weather a region will experience. President
Johnson, when Vice-President and Chairman of the National Aeronautics
and Space Council, estimated the saving which our nation could
realize if accurate weather predictions were available only
five days in advance. These yearly savings include: $2.5 billion
in agriculture; $45 million in the lumber industry; $100 million
in surface transportation; $75 million in retail marketing;
and $4 billion in water resources management. Beyond these dollar
savings, we have the priceless savings in human life which result
when hurricanes, tidal waves, and the like are detected in advance.
Clearly, then, research into the nature of weather will have
a profound effect upon our welfare. /p>
Until early 1960, meteorologists were somewhat earth-bound
in their measurements of weather phenomena. True, aircraft and
weather balloons were launched to measure wind speed, barometric
pressure, and other weather variables. Later, sounding rockets
were also used to obtain these measurements. But these measurements
are somewhat localized in that only a small region of the atmosphere
or stratosphere is sampled. And, as we know, weather is by no
means predictable by immediate local conditions. A storm front
in the far reaches of Canada's Hudson Bay on Tuesday can create
havoc with cattle ranches in North Dakota on Thursday. Even
with many remote weather stations positioned at strategic points
around the world, severe weather conditions can be building
up while unobserved by these stations. A system for weather
surveillance which could survey large sectors of the earth was
urgently needed.
The Tiros Satellite System
TThe Tiros (Television Infra-Red Observation Satellite) series
provides a partial solution to this requirement. These vehicles,
equipped with television cameras and infrared (IR) radiometers,
gather data for analysis by meteorologists within hours after
the observation. The first in the series, Tiros I, was launched
from Cape Kennedy on April 1, 1960. At this writing, ten Tiros
satellites have been launched.
Table 1. Specs for Thor-Delta booster which
launched Tiros.
The iros is an 18-sided vehicle, 22 inches high by 42 inches
in diameter, weighing about 300 pounds. Each of the 18 faces
of the satellite is an array of solar cells. These 900 solar
cells furnish charging current for the 63 nickel-cadmium cells
which furnish power throughout orbit. Two 18·inch receiving
antennas extend from the top of the satellite and are used to
receive ground commands. Four 22-inch telemetry transmitting
antennas are located on the underside of the package. Tiros
I through VIII had two vidicon TV cameras mounted on the underside
of the satellite. Later Tiros spacecraft have side-looking TV
cameras mounted on opposite sides.
This view of the Nile River and its Delta,
the Red Sea, and the eastern Mediterranean was taken by Tiros
III from an altitude of 400 miles.
The Tiros series is put into orbit by the three-stage ThorDelta
launch vehicle. Table 1 gives important specifications for this
space booster. For some perspective, recognize that jet engines
used on modern commercial airliners have typical ratings of
16,000 pounds thrust per engine. Hence, the first stage alone
of the launch vehicle delivers more thrust than ten of these
aircraft engines. Launch vehicles have since been developed
which generate more than two million. pounds of thrust.
The vortex of the Hurricane Daisy photographed
several year ago off the east coast of the United States by
the Tiros V satellite.
Tiros orbits range from 450 miles to 860 miles, with periods
(time for one revolution) of 90 minutes to 113 minutes, respectively.
At the 450-mile orbit a region on earth of 800 to 1000 miles
in diameter is covered by one transmitted TV picture.
Tiros I through VIII were placed in a general east-west orbit,
resulting in coverage of about 25% of the earth's surface. Later
Tiros launches resulted in a north-south, or polar orbit. The
polar orbit permits coverage of nearly all the earth's surface.
The polar orbit is also selected so as to be nearly synchronous
with the sun. The sun-sync orbit results in backlighting from
the sun during the northward pass of the satellite, producing
high-quality photographs.
The Tiros VII being checked out prior to
its launch into space.
Tiros I-VII made use of a focal-plane shutter in conjunction
with the two vidicon TV cameras. Pictures are stored on the
tube face and converted to data bits for storage on magnetic
tape or direct readout by ground stations. Each orbit results
in 64 pictures, or 32 pictures per tape. Transmission of data
to the ground station requires about three minutes. The data
transmission simultaneously erases the magnetic tapes for the
next data-gathering pass. The operation of the readout system
as well as the timing of the picture-taking sequence is accomplished
by ground command. The ground command sets timers which activate
the camera system when the satellite passes over the region
of interest.
The APT ground receiving system uses fairly
simple, inexpensive ground-based equipment which employs conventional
facsimile recorder.
Starting with Tiros VIII, a new system of data readout was
used. The new system is designated Automatic Picture Transmission
(APT). Rather than construct a TV picture line by line, electronically
photograph the screen, and then store or transmit, APT uses
a system similar to that used by newspapers and the press services
to transmit photos. A facsimile recorder then reproduces the
picture as received.
Ground receiving stations for Tiros are Wallops Island,
Virginia; San Nicolas, California; and Fairbanks, Alaska. Over-all
direction of the Tiros system stems from Goddard Space Flight
Center, Greenbelt, Maryland. These stations are capable of receiving
data when the satellite draws to within 1500 miles of the station.
The received pictures are photographed by 35-mm camera for immediate
analysis by meteorologists. In particular, these photos reveal
conditions of cloud cover as well as the presence of hurricane
conditions.
In addition to the TV camera, infrared radiometers
measure the amount of reflected and absorbed solar IR energy.
The amount of IR energy absorbed and reflected determines the
heat balance of the earth and therefore affects the weather.
The IR data is transmitted and received as non-photographic
data. This data is later reduced and plotted on weather maps
for analysis. While the IR data is not immediately useful to
meteorologists, it nevertheless provides a kind of long-range
weather behavior of our planet.
The initial design of
Tiros called for a mission life of three to four months. The
first Tiros was operational for 2 1/2 months. Later Tiros vehicles
operated for well over one year. In the first three years of
operation some 300,000 TV photographs were transmitted. Tiros
I completed 1302 orbits and relayed 22,592 pictures to ground
stations.
As seen in the accompanying photographs, Tiros
has produced some startling results. Of particular importance
were other photos taken by Tiros III in Sept. 1961. These photos
revealed the build-up of Hurricane Carla. As a result of this
early warning, approximately 350,000 persons withdrew from the
storm region involved and injuries and loss of life were held
to an absolute minimum.
Second-Generation Satellites
In addition to the ten Tiros launchings, two each ESSA
(Environmental Survey Satellite) and the Nimbus satellites that
have been orbited.
The ESSA satellites are similar to
the earlier Tiros systems and operate in the "cartwheel" mode.
ESSA I was launched on February 3, 1966 and carried two half-inch
vidicon TV cameras into a circular 460-mile-high polar orbit,
having a period of about 100 minutes. ESSA II carried two APT
cameras into a circular 860-mile-high polar orbit with a 113-minute
period. NASA plans to keep two ESSA satellites in orbit at all
times. As one ESSA vehicle ceases to transmit, a replacement
will be launched. The ESSA satellites represent the operational
system for which the Tiros vehicles were the research and development
packages.
The Nimbus represents a more sophisticated
weather satellite system. In particular, Nimbus is not restricted
to photographing the earth during daylight. By means of its
high-resolution red radiometer (HRIR) system, night photos are
obtained. These photos appears as dark or light regions, depending
on whether more or less heat is radiated, respectively.
In addition to the HRIR system, three vidicon cameras are used.
From an orbit of 575 miles, resolution of one-half mile is possible.
The APT system was also flown on the Nimbus.
Nimbus
I was moderately successful after launch on August 28, 1964.
The second stage of the launch vehicle did not burn as long
as required, resulting in an elliptical orbit of 252 miles perigee
and 578 miles apogee, rather than the planned circular 575-mile
orbit. The satellite transmitted many useful photos until a
solar panel locked and was thus unable to track the sun. As
a result, Nimbus I ceased on September 23, 1964.
Nimbus
II was successfully launched May 15, 1966, carrying HRIR, APT,
and vidicon systems. NASA plans to launch a Nimbus satellite
approximately every 18 months. These vehicles will serve to
test new systems for improved weather observations .
The Tiros vehicles and successors form the Tiros Operational
System (TOS), which is a joint undertaking of the U.S. Weather
Bureau and NASA. In addition to the benefits already listed,
the Tiros system may provide scientists with new insight into
such phenomena as clear-air turbulence (CAT) and the nature
of the "jet-stream."
Perhaps history will someday
show that Tiros provided a significant advance toward a goal
we have desired, control of the weather. A system of sophisticated
Tiros-like satellites, relaying weather data to a central computer
which directs corrective (and as yet unknown) action to smooth
the weather, is presently but a dream. But the translation from
dream to design to hardware has been foreshortened considerably
as our technology advances.
Posted 2/29/2012
