A satellite was launched for the first time with frequency division multiple access in 1966. After functioning for nearly 20 years, it slipped into a useless orbit almost 7 years after official deactivation

NASA satellite ATS-1 was launched on December 7, 1966, to explore weather observation, satellite communications and spacecraft operations. It is a communications technique that combines independently transmitted signals for delivery over a single downlink carrier. It also included a spin-scan cloud camera to capture images of the sun-lit side of Earth from a geostationary orbit.

NASA's ATS-1 was part of the agency's Applications Technology Satellite program, which built upon the work of experimental communications satellites launched in the early 1960s. Its mission included experiments related to communications as well as weather observations and the space environment.

The satellite looked to test geostationary satellite operations, study conditions in orbit and relay meteorological information to ground stations. Its communications equipment, weather camera and data relay capabilities contributed to NASA's research on satellite technology.

What was ATS-1, and why did NASA launch it?

ATS-1 was a weather and communications satellite launched on December 7, 1966, from Cape Canaveral, Florida, on an Atlas Agena D rocket. ATS-1 was based on the design of the Syncom communications satellites, but it was larger and included more equipment.

The spacecraft weighed approximately 750 pounds (340 kg), according to one set of spacecraft specifications. Another description lists the spacecraft's on-orbit mass as 351.5 kg (775 lbs.). The spacecraft was about 56 inches in diameter and 57 inches high.

How ATS-1 introduced frequency division multiple access?

ATS-1 was the first satellite to use frequency division multiple access, a communications technique that combined independently transmitted signals for delivery over a single downlink carrier.

Since a separate downlink carrier wave was not needed for each independently received signal, multiple signals could be relayed over one carrier. ATS-1's capability to relay multiple independently transmitted signals was an important part of its communications experiments.

In addition to its FDMA experiment, ATS-1 included a C-band transponder. First generation ATS spacecraft included C-band transponders with 25 MHz bandwidth. They had the capacity to relay 1,200 one-way voice circuits or one color television signal.

Besides its C-band communications equipment, ATS-1 carried a VHF communications experiment. It was intended to support communications with aircraft, ships and meteorological remote terminals. ATS-1's communications experiments included an eight-element phased array antenna system, with each element having a 5-watt transmitter.

How ATS-1 captured images of the entire Earth?

One of the spacecraft's major experiments was its spin-scan cloud camera. It provided researchers with full disk images of the sun-lit side of the Earth from a geostationary orbit.

In 1966, the camera captured some of the first high quality images of cloud cover from an equatorial synchronous satellite. The images spanned the portion of the Earth between approximately 52 degrees north and 52 degrees south latitude.

The camera used the spacecraft's spinning to scan the surface of the Earth, which created successive lines that were combined to form an image of the visible hemisphere.

The images had a resolution of approximately 3.2 kilometers. The camera could capture a full disk image in about 20 minutes, then needed approximately 10 minutes to reset before it could take another picture. Images could be used to support research on weather systems and their development.

How the ATS programme developed?

NASA and Hughes had initially considered developing an Advanced Syncom spacecraft. However, there were concerns raised in Congress that NASA was pursuing technology development for Comsat, a private company. As a result, the program was expanded to include a broader range of experiments in addition to communications.

The Department of Defense also played a role in the program. It encouraged NASA to investigate gravity-gradient stabilization on ATS-2, ATS-4 and ATS-5. Medium altitude orbit technology was another area of interest, including on ATS-2.

The first five ATS spacecraft had a common C-band communications capability. Their transponders had a bandwidth of 25 MHz and could relay 1,200 one-way voice circuits or one color television signal. As a result, the program provided an opportunity to conduct experiments in a variety of areas related to future communications and spacecraft missions.

When was ATS-1 deactivated, and what happened afterwards?

ATS-1 was placed in a transfer orbit over the equator near Ecuador. This orbit caused the spacecraft to drift westward over the years. Eventually, it was located at 151 degrees west longitude, east of Christmas Island in the Pacific Ocean.

Although ATS-1 had a recorded lifetime of about 12 years, useful data was obtained during its first six years of operation, from 1966 to 1972. The spacecraft's communications equipment continued to function after its official deactivation, but in 1985, ATS-1 failed to respond to commands, and drifted into a useless orbit. This ended the spacecraft's ability to continue its experiments.