Rescuing Astronauts and Televising a Moon Landing
How NASA’s Deep Space Network keeps contact with distant spacecraft
After reading about how the Deep Space Network (DSN) will be used to communicate with the James Webb Space Telescope at the second Sun-Earth Lagrange point following its launch planned for 2021, I wanted to learn more about this worldwide network of facilities and how its three locations were chosen. The DSN consists of antennas at the Goldstone Communications Complex near Barstow, California, the Madrid Deep Space Communications Complex in Spain, and the Canberra Deep Space Communication Complex near the Australian capital. The three locations are spaced roughly 120° apart in longitude around the globe, which allows constant observation of spacecraft. As the Earth rotates and an object is about to dip below the horizon at one site, the signal can be picked up by the next antenna.
Unlike objects in low Earth orbit (which are also supported by the DSN), spacecraft in Deep Space are visible from a large portion of the Earth’s surface for long periods of time. Objects that are over 30,000 km above the surface are always visible from one of the DSN tracking stations, however their signals are often so faint that highly sensitive receivers and powerful transmitters are required to communicate with them. The DSN makes it possible to acquire data from spacecraft, track their position and velocity, and transmit commands and software modifications.
In 1957, in the midst of the Cold War, the world’s first artificial satellite, Sputnik 1, was launched by the Soviet Union. This was followed by a period known as the “Sputnik crisis”, in which the public in Western nations feared that the USSR had surpassed the rest of the world in advancements in space technology. NASA was yet to be formed and the Jet Propulsion Laboratory (JPL) was under the control of the U.S. Army. JPL manufactured the first successful U.S. Satellite, Explorer 1, and established radio tracking stations in California, Singapore and Nigeria to follow its progress. When NASA took control of the JPL soon after, an economical decision was made to create a single communications network that could be used for all deep space missions. Since JPL is located near Los Angeles, it makes sense that the Mojave Desert was selected as the first location.
The DSN has been designed to receive extremely faint signals from distant spacecraft, so Goldstone was carefully chosen to be isolated from radio and television transmitters, as well as power lines, which can make it difficult to uncover the weak spacecraft signals. In fact, each of the three stations is situated in a bowl-shaped, semi-mountainous region, in order to shield the receivers from radio interference.
It was the DSN that showed us the first footage of Neil Armstrong walking on the moon in 1969, and it also played a critical role in bringing the Apollo 13 astronauts safely back to Earth, following the rupture of an oxygen tank. Normal operation uses smaller, more economical antennas, but in this case the spacecraft needed to use the majority of its limited power for re-entry, rather than communications. It was still necessary for engineers on the Earth to maintain contact with the astronauts, which meant that the largest antennas in the DSN were essential for saving the lives of the crew. This emergency service has also been made available to other space agencies in the spirit of international cooperation.
As well as its primary purpose of spacecraft communication, the DSN is also used to make direct scientific observations. The dishes observe radio sources, such as pulsars and quasars, and also provide information about the properties of other planets due to changes in the radio link between orbiting or nearby spacecraft and the DSN. The DSN also uses radar astronomy, where waves bounce off astronomical objects like asteroids, producing radar images. The DSN even teaches us about changes in the Earth’s crust, as radio signals from astronomical sources take a different amount of time to reach each station.
The Deep Space Network is a world leader in space communications and research, and a significant example of international scientific cooperation. Public tours are available at all three stations, so if you find yourself near Barstow, Madrid or California, you can see for yourself how each location has been chosen to allow distant spacecraft to phone home.
