Communications Out in Space.
One of the most dramatic telephone conversations ever to ake place occurred on July 20, 1969 when President Richard Nixon talked to Astronauts Buzz Aldrin and Neil Armstrong who were 240,000 miles away, on the surface of the Moon!
The millions of Americans listening in first heard Capcom radioing the astronauts saying: "Tranquility Base, this is Houston. Could we get you both on camera for a minute, please? Neil and Buzz, the President of the United Sttes is in office now and would like to say a few words to you. Over."
From the Moon, Armstrong responded: "that would be an honor." Down in Houston, Capcom got out the three-way conversation, saying: "Go ahead, Mr. President. This is Houston. Out."
And then President Nixon spoke to the first men on the Moon, saying: "Neil and Buzz, I am talking to you from the Oval Room at the White House. And this certainly has to be the most historic telephone call ever made. I just can't tell you how proud we all are . . .
What a great moment in communications!
Within the past year NASA (the Natinal Aeronautics and Space Administration) celebrated its 25th birthday. During the agency's first quarter century, 12 astronauts have walked on the Moon and dozens of astronauts and scientists have worked in low earth orbit. The planets Mercury, Venus, Mars, Jupiter, and Saturn have been explored. And the launching of communications satellites has allowed us to see events anywhere on Earth.
The voice communications with men in space . . . heard clearly by Americans on their own radios and television sets . . . had to be the most dramatic communications happenings of these two dynamic decades.
When Astronaut Allan Shepard became America's first man in space, an excited citizenry hung on every word he radioed back from his Mercury 3 spacecraft during his 15 minutes and 22 seconds aloft.
During each manned space flight the casual, laconic and almost clinical conversations between the men in space and "Ground Control" at The Cape and "Mission Control" in Houston Became almost an "art form", captivating listening Americans during each mission.
The complex communications system which has made these space conversations on effective has reached its highest level of sophistication in support of the space shuttle program.
NASA's Spaceflight Tracking and Data Network (STDN) is a worldwide system that provides continuous and instantaneous communications with the Shuttle orbiter and crew. The network is maintained and operated by NASA's Goddard Space Flight Center at Greenbelt, Maryland.
The network for the Shuttle orbiter flight program consists of 18 ground stations equipped with 14, 30, 40 and 85-foot S-band antenna systems and C-band radar systems, the NASA Communications System (NASCOM) augmented by 15 Department of Defense geographical locations providing C-band support and one Defense 60-foot S-band antenna system. In addition, there are six major computing interfaces located at Goddard--Network Operations Control Center (NOCC at Goddard): Western Space Satellite Control Facility, Sunnyvale, California; White Sands Missile Range, New Mexico; and Eastern Space and Missile Center, Florida, providing real-time computational support.
The network has support agreements with the governments of Australia, Spain, Senegal, Botswana, Ecuador, chile, the United Kingdom and Bermuda to provide NASA tracking stations support to the Shuttle program.
The tracking network is linked by the NASA Communications Network (NASCOM), from which all information flows to and from Mission Control Center at the Space Center in Houston.
The communications network consists of more than two million circuit miles of diversely routed communications channels. It uses domestic and international communications satellites, submarine cables and terrestrial landlines and microwave radio systems to interconnect the many tracking stations, launch and orbital control centers and other supporting locations.
The hub of the communications network is the main switching center at Goddard. From Goddard, personel direct overall network operation, including those at supporting NASCOM switching centers in Madrid, Spain; Canberra, Australia; and Jet Propulsion Laboratory, Pasadena. Additional support activities are provided by Air Force communications centers at Cape Canaveral and Vandenberg AFB.
A key change in the communications network has been the implementation of two simultaneous air-ground S-band voice circuits in addition to UHF radio capability. In previous Apollo missions only one S-band circuit was provided Telemetry data circuitry from tracking stations was increased in size to handle 128 kb/s in previous programs. Correspondingly, the command data circuit to a station was increased from 7.2 kb/s to a 56 kb/s capability.
During previous manned program support, use of commications satellites was limited to those of Intelsat to connect the United States with foreign locations. Since then, domestic communications satellites have become available and they now play a key role in extending voice, data and television signals from key locations and stations in the United States. They also provide for extending data between Goddard and foreign locations as well as between Goddard and Johnson.
Among the providers of communications services for early shuttle flights was the Bell System, which provided a specially designed network to NASA, tying together hundreds of NASA locations around the world . . . as far away as Africa and Australia . . . to help space agency officials track the Shuttle and exchange information during the flight.
NASA officials in 58 locations are able to discuss flight developments over their nationwide teleconferencing system. AT&T Long Lines installed nine of these teleconferencing rooms especially for the initial voyage of the Shuttle.
Also at White Sands, Mountain Bell recently installed a microwave system that allowed AT&T Long Lines to set up a private eight-circuit link between as NASA tracking site at the missile range and a data analysis unit at the Goddard Space Center in Green Belt, Maryland. This system will remain in place for use during future Shuttle flights.
An extensive portion of the domestic voice, wideband data and video communications services used by NASA in support of and flight were also carried over the RCA American Communications Satcom satellite system.
RCA Americom's Shuttle network consisted of 10 dedicated earth stations on government property at eight locations. This network was designed to carry 11 wideband data services, 28 voice and alternate voice-data narrowband services and the major portion of the Shuttle television broadcast network between these locations and the public. Further expansion on these services will be provided by RCA in support of the operation of NASA's Tracking and Data Relay Satellite System (TDRSS) in 1982.
Currently, wideband data links vary in rate from 56 kb/s to 1.544 Mb/s, and are used between Goddard and Johnson Space Flight Centers for main and alternate backup handling telemetry and command data.
All of the voice and communications between the astronauts and the ground during a Shuttle flight were spoken over an audio distribution system (ADS) supplied by Telephonics Corporation of Huntington, New York. The ADS is the Shuttle's main voice communications subsystem. Short of external transmission and reception, the system provides an onboard 23-station audio link, as well as a means for switching incoming and outgoing between the spacecraft and ground control.
The system also permits the crew to communicate with other spacecraft and astronauts operating outside the Shuttle, a consideration that will become most important with future missions.
Dramatic and exciting as the space voice communications are, perhaps the most meaningful space communications of the decade are the signals coming back to earth from unmanned spacecraft.
On July 20, 1976 . . . seven years to the day after Astronauts Aldrin and Armstrong landed on the Moon . . . Viking I landed safely on the surface of Mars after an 11-month flight, a highlight of America's bicentennial celebration.
Almost immediately upon landing, one of the two facsimile cameras photographed the area near the lander and one of its foot pads. Next came a sweeping 300-degree panoramic view of the landscape. The picture data was relayed to the orbiter at a rate of 16,000 b/s. From the orbiter the data was sent back to Earth at slower rate of 4,000 b/s because of the great distance involved. These first images, in black and white, were later followed by color views.
Obviously, high-reliability of all components was a prime consideration for the success of the mission. Without communications, there would be no way to bring back the valuable scientific data.
The RCA communications system aboard the lander consisted of a relay link between the orbiter and lander and a direct link connecting the lander and Earth. UHF radio was used to relay scientific data to the orbiter and an S-band transmitter on the lander sends data directly to Earth. Throughout its 11-month voyage to Mars, the lander's communications system was dormant to conserve power, and was activated only seconds prior to the lander's separation from the orbiter, about 11,300 miles above Mars.
The relay link was the primary means of communication during descent and landing until a direct link between the lander and Earth was established on the surface of Mars.
When the lander separated from the orbiter and descended into the Martian atmosphere, UHF signals began transmitting real-time data at 4,000 b/s at a frequency of 381 MHz to the orbiter. This information consisted of entry science data, such as pressure and temperature of the Martian ionosphere and atmosphere, and engineering information related to the lander's operating performance.
The lander's antennas were developed by RCA's Missile and Surface Radar Division.
The UHF low-gain antenna on the lander is 18 inches long, and sends data from the lander to the orbiter for relay to Earth. The S-band low-gain antenna is six inches high and receives signals from Earth command, radio tracking and science and engineering data return.
The most amazing space communications achievement of these two dramatic decades is the success of Pioneer 10 which left Earth in March of 1972 and a 21-month mission to Jupiter and which is still transmitting information back to earth from the outer limits of the solar system!
As we go to press with this "20th Anniversary Issue" Pioneer continues to relay information to scientists on Earth. In fact, Pioneer 10 has now transmitted well over 126 billion bits of scientific data and traveled almost four billion miles from Earth!
Pioneer 10 still has work ahead, as it seeks gravity waves and a tenth planet. Barnard's Star, a small, cool, red star and one of the Sun's closet neighbors, at a distance of 3.8 light yers in 10,507 years.
As Pioneer 10 continues to trek away from Earth at a speed of around 30,000 miles per hour (roughly 5,000 miles per hour above the speed necessary to escape the solar system), its radio signals to Earth become increasingly faint. Current it takes a signal from the spacecraft about five hours to reach Earth, and this time interval increases by about a minute every four days.
In addition, the spacecraft's eight-watt transmission (whose power is about equal to that of a miniature light bulb) is weakened to a barely detectable few-thousand-trillionths of a watt by the time it reaches radio receiving antennas on EArth. Still, NASA scientists hope to track Pioneer 10 through its radio signals for seven more years, at which time it will be at a distance of five billion miles from Earth.
The voice of a man coming to us from the moon, pictures coming back to us from the surface of Mars, faint signals reaching us from a man-made spacecraft now four billion miles out in space . . . all "science fiction" stuff just a few short years ago . . . are the dramatic reality of space communications in our two dynamic decades.
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|Date:||Sep 1, 1984|
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