September was a busy month for the IEEE Milestones in Electrical Engineering and Computing program. Three achievements were honored: the discovery of radioconduction, radio astronomical observations using very long baseline interferometry, and the first weather satellite.
In the late 1800s, German physicist Heinrich Hertz discovered the existence of electromagnetic waves that could be detected a short distance away from their source. For a detector, he used a wire loop in which sparks jumped a small gap. In no time, the search was on for a device that could detect electromagnetic waves over a longer distance. That was difficult because such waves would be very weak when they arrived at the detector.
The challenge sparked the interest of Edouard Branly, a French inventor, physicist, and professor at the Catholic Institute of Paris. In 1890 Branly began searching for a more sensitive detector and was inspired by the unusual change in the resistance of thin metal films when exposed to electric sparks. Later that year, he succeeded in his quest. He developed what was called a coherer and with it discovered that the resistance of metal filings changed in the presence of electromagnetic waves, an effect referred to as radioconduction.
His coherer was a primitive radio signal detector that consisted of a glass tube filled with sharp zinc and silver filings. By attaching a wire to each tube end and running a current through the filings as the electromagnetic waves hit them, the resistance of the filings, and the current through them, varied in response to the waves. And with the coherer, the electromagnetic waves acting upon the filings could be made to switch another current—which could be made much stronger—on or off.
Branly’s discovery and development of the coherer made communications over long distances possible. Today, he is revered in France as the inventor of wireless telegraphy.
On 23 September at the Catholic Institute of Paris, IEEE honored Branly’s discovery of radioconduction in a Milestone ceremony. A plaque was placed at the Catholic Institute of Paris that reads:
In this building, Edouard Branly discovered radioconduction, now called the Branly Effect. On 24 November 1890, he observed that an electromagnetic wave changes the ability of metal filings to conduct electricity. Branly used his discovery to make a very sensitive detector called a coherer, improved versions of which became the first practical wireless signal receivers.
Radio astronomers study celestial objects that emit radio waves but are often invisible in other parts of the electromagnetic spectrum. Very long baseline interferometry (VLBI) is one of the most powerful techniques used to produce high-resolution images of such distant radio sources. It works by combining the signals of a network of widely dispersed telescopes to form a single powerful telescope. The method provides a better angular resolution than any single optical telescope, allowing astronomers to investigate such theories as the existence of black holes in galaxy cores, as well as to test fundamentals of high-energy physics. The technique is also used in geodesy, the science that measures features on Earth and in the solar system.
Prior to VLBI, short-baseline interferometry was used for high-resolution imaging. In that technique, cables or radio links connected two or more radio antennas to signal-processing equipment. The distance, or baseline, between pairs of antennas became longer and longer over time, and it soon became clear that important astrophysical questions could be answered only by building interferometers with even greater baselines—which brought VLBI to the fore.
Discussions about the feasibility of VLBI began in 1960 at research institutions around the world. In subsequent years, scientists worked on developing telescopes using VLBI to make radio astronomical observations. They included researchers at MIT; the Dominion Radio Astrophysical Observatory (DRAO), in Penticton, B.C., Canada; and Cornell University, in Ithaca, N.Y. The breakthrough came in 1967 when the DRAO research group made the first such observation with its radio telescope and another at the Algonquin Radio Observatory, more than 3000 kilometers away.
A ceremony was held at DRAO on 23 September to mark that feat, and a Milestone plaque was placed at the base of the observatory’s radiotelescope that reads:
On the morning of 17 April 1967, radio astronomers used this radio telescope at DRAO and a second one at the Algonquin Radio Observatory located 3074 km away to make the first successful radio astronomical observations using very long baseline interferometry. Today, VLBI networks span the globe, extend into space, and continue to make significant contributions to both radio astronomy and geodesy.
FIRST WEATHER SATELLITE
After the USSR’s launch of Sputnik in 1957, the United States sought a project with which to respond quickly. The U.S. Department of Defense came up with a plan to build a satellite to observe Earth and to provide advance warning of hurricanes and other severe weather.
Named Project TIROS (television infrared observation satellite), work began at the DOD, but the project was transferred in April 1959 to NASA, the new space agency.
At the time, television cameras used a small imaging sensor developed in 1956 by RCA Laboratories of Princeton, N.J., that had sufficient light sensitivity and resolution for TIROS. But the lab was contracted by DOD in late 1957 to improve the cameras’ electronics and reduce their size and weight. RCA formed its Astro-Electronics Division to focus on TIROS and other science missions. In the next few years, researchers there and at other RCA facilities, including the David Sarnoff Research Center, also in Princeton, developed the satellite’s structure, dynamic controls, and power and communications systems.
TIROS I had two television cameras (wide and narrow angle), tape recorders to store data when out of acquisition range of Earth, and radiometers to measure reflected solar and emitted infrared radiation from Earth and its atmosphere.
The satellite was launched from Cape Canaveral, Fla., on 1 April 1960, becoming the world’s first meteorological satellite. It made 1392 orbits in its three-month life, and took nearly 23 000 pictures. In the following years, nine more TIROS satellites were launched.
A ceremony was held 27 September at the former RCA Labs, now the Sarnoff Corp. A plaque was placed inside the facility that reads:
On 1 April 1960, the National Aeronautical and Space Administration launched TIROS I, the world’s first meteorological satellite, to capture and transmit video images of the Earth’s weather patterns. RCA staff at Defense Electronics Products, the David Sarnoff Research Center, and the Astro-Electronics Division designed and constructed the satellite and ground station systems. TIROS I pioneered meteorological and environmental satellite television for an expanding array of purposes.