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.
As time permits, I will be glad to scan articles for you. All copyrights (if any) are hereby acknowledged.
Table 1. Specs for Thor-Delta booster which launched Tiros.
The Tiros 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.
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
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.
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 May 27, 2012