Your RF Cafe
March 1967 Electronics World[Table of Contents] People old and young enjoy waxing nostalgic about and learning some of the history of early electronics. Electronics World was published from May 1959 through December 1971. All copyrights are hereby acknowledged. See all Electronics World articles.
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.
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.
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.
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.
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.
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.
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.
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.