The Deep Space Network:
NASA’s Link to the Solar System
Note from the Editors: This issue’s lead article is the tenth in a series of reports describing the history and current activities of the planetary research facilities funded by NASA and located nationwide. This issue features the Deep Space Network, a worldwide network of spacecraft communication facilities that supports NASA’s interplanetary spacecraft missions. — Paul Schenk and Renée Dotson
From Mercury to Pluto (and beyond), we have marveled at the stunning vistas found throughout our solar system. From erupting volcanos on Io to the glorious rings of Saturn, it is easy to forget that we would never know about these marvels were it not for one key global NASA facility. The Deep Space Network (DSN) is NASA’s international array of giant radio antennas that supports interplanetary spacecraft missions. It’s the largest and most sensitive scientific telecommunications system in the world, and is responsible for communicating with and receiving terabits of data from the armada of spacecraft touring our solar system. The DSN also provides radar and radio astronomy observations that improve our understanding of the solar system and the larger universe.
The DSN is operated by NASA’s Jet Propulsion Laboratory (JPL), which also operates many of the agency’s interplanetary robotic space missions. Other space agencies, such as Europe’s European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), also use the DSN through cooperative agreements. The DSN consists of three major facilities spaced equidistant from each other‚ approximately 120° apart in longitude‚ around the world. These sites are at Goldstone, near Barstow, California; near Madrid, Spain; and near Canberra, Australia. The strategic placement of these sites permits constant communication with spacecraft as our planet rotates; before a distant spacecraft sinks below the horizon at one DSN site, another site can pick up the signal and continue communicating.
The antennas of the DSN are the indispensable link to explorers venturing beyond Earth. They provide the crucial connection for commanding our spacecraft and receiving their never-before-seen images and scientific information on Earth, propelling our understanding of the universe, our solar system, and ultimately, our place within it.
The forerunner of the DSN was established in January 1958, when JPL, then under contract to the U.S. Army‚ deployed portable radio tracking stations in Nigeria, Singapore, and California. That month, when the Army successfully launched Explorer 1, the first successful U.S. satellite, these stations received telemetry and helped mission controllers plot the spacecraft’s orbit. NASA was officially established in October of that year to consolidate the separately developing space exploration programs of the Army, Navy, and Air Force into one civilian organization.
On December 3, 1958, JPL was transferred from the Army to NASA and given responsibility for the design and execution of lunar and planetary exploration programs using robotic spacecraft. Shortly afterward, NASA established the concept of the DSN as a separately managed and operated communications facility that would accommodate all deep space missions. This model would remove the need for each flight project to acquire and operate its own specialized space communications network. The DSN was given responsibility for its own research, development, and operations in support of its users. Under this model, it has become a world leader in the development of deep space communications and navigation.
NASA’s human spaceflight program, based at what is now Johnson Space Center in Houston, originated at Langley Research Center in Virginia via an organization called the Space Task Group. It was set up before Apollo for the Mercury program in the early 1960s. The Mercury and Gemini programs used a ground-based tracking and communication system called the Manned Space Flight Network, which was operated by the Goddard Space Flight Center in Maryland. The 2000 movie The Dish, starring Sam Neill, tells the story (with the usual Hollywood embellishment) of the use of the Parkes Observatory radio telescope in Australia near the present Canberra station as part of this network for tracking Apollo 11.
The Apollo program needed full-time communications support and JPL was busy with its own missions, so DSN engineers helped design and operate a “parallel network.” After the Apollo program ended, the DSN inherited this equipment. The Gemini-era network could not be adapted for spacecraft outside Earth orbit, so they opted to clone the array of giant radio antennas used by JPL’s DSN. Since that time, the DSN has kept the legacy alive by providing communications for a very long roll call of missions for NASA and other space agencies. Managed by JPL, the DSN will play a central role in NASA’s Artemis lunar explorations and the agency’s plans for astronauts to one day go beyond the Moon to Mars.
The DSN has three main sites. The Australian complex is located 40 kilometers (25 miles) southwest of Canberra near the Tidbinbilla Nature Reserve. The Spanish complex is located 60 kilometers (37 miles) west of Madrid at Robledo de Chavela. The Goldstone complex is located on the U.S. Army’s Fort Irwin Military Reservation, approximately 72 kilometers (45 miles) northeast of the desert city of Barstow, California. Each complex is situated in semi-mountainous, bowl-shaped terrains to shield against external radio frequency interference.
Each of the three DSN sites has multiple large antennas and is designed to enable continuous radio communication between several spacecraft and Earth. All three complexes consist of at least four antenna stations, each equipped with large, parabolic dish antennas and ultra-sensitive receiving systems capable of detecting incredibly faint radio signals from distant spacecraft. The DSN’s large antennas are focusing mechanisms that concentrate power when receiving data and when transmitting commands. The antennas must point toward the spacecraft with extreme accuracy, because an antenna can “see” only a tiny portion of the sky (not unlike looking at the sky through a soda straw).
To detect the spacecraft’s faint signal, the antennas are equipped with amplifiers, but there are two problems. First, the signal becomes degraded by background radio noise, or static, emitted naturally by nearly all objects in the universe, including Earth and the Sun. The background noise gets amplified along with the signal. Second, the powerful electronic equipment amplifying the signal adds noise of its own. The DSN uses highly sophisticated technology, including cooling the amplifiers to a few degrees above absolute zero, and special techniques to encode signals so the receiving system can distinguish the signal from the unwanted noise.
Antenna stations are remotely operated from a signal processing center at each complex. These centers house electronic systems that point and control the antennas, receive and process data, transmit commands, and generate spacecraft navigation data. Once the data is processed at the complexes, it is transmitted to JPL for further processing and distribution to science teams over a ground communications network.
But the DSN is much more than a collection of big antennas. It is a powerful system for commanding, tracking, and monitoring the health and safety of spacecraft at many distant planetary locales. The DSN also enables powerful science investigations that probe the nature of asteroids and the interiors of planets and moons.
Telemetry data is made up of crucial science and engineering information transmitted to Earth via radio signals from spacecraft as they explore the far reaches of our solar system. The DSN acquires, processes, decodes, and distributes this data. Space mission operations teams use the DSN Command System to control the activities of their spacecraft. Commands are sent to robotic probes as coded computer files that the craft execute as a series of actions. The DSN Tracking System provides two-way communication between Earth-based equipment and a spacecraft, making measurements that allow flight controllers to determine the position and velocity of spacecraft with great precision. DSN antennas are used by some space missions to perform science experiments using the radio signals sent between a spacecraft and Earth. Changes in radio signals between their transmission and receipt can provide lots of useful information about distant places in the solar system, a technique being used by Juno to probe the interior of Jupiter. Other examples include probing the rings of Saturn, revealing the interior structure of planets and moons, and testing the theory of relativity.
In addition, its vital role as the communications hub for deep space exploration, the DSN is also used as an advanced instrument for scientific research, including radio astronomy and radar mapping of passing asteroids. A similar role is played by the Arecibo Observatory radio telescope in Puerto Rico, as well as other radio antennae across the globe.
The DSN must continually adapt to the expanding needs of NASA’s exploration community and upgrade its equipment to keep pace with engineering improvements. Surrounded by California desert, NASA officials broke ground this past winter on a new antenna for communicating with the agency’s farthest-flung robotic spacecraft. The 34-meter-wide (112-foot-wide) antenna dish currently under construction represents a future in which more missions will require advanced technology, such as lasers capable of transmitting vast amounts of data from astronauts on the lunar or martian surface. As part of its Artemis program, NASA may send the first woman and next man to the Moon by 2024, applying lessons learned there to send astronauts to Mars.
Using massive antenna dishes, the agency talks to more than 30 deep space missions on any given day, including many international missions. As more missions have launched and with more in the works, NASA is looking to strengthen the network. When completed in 2.5 years, the new dish will be christened Deep Space Station-23 (DSS-23), bringing the DSN’s number of operational antennas to 13. “Since the 1960s, when the world first watched live pictures of humans in space and on the Moon, to revealing imagery and scientific data from the surface of Mars and vast, distant galaxies, the Deep Space Network has connected humankind with our solar system and beyond,” said Badri Younes, NASA’s deputy associate administrator for Space Communications and Navigation (or ScaN), which oversees NASA’s networks. “This new antenna, the fifth of six currently planned, is another example of NASA’s determination to enable science and space exploration through the use of the latest technology.” The first addition to Goldstone since 2003, the new dish is being built at the complex’s Apollo site, so named because its DSS-16 antenna supported NASA’s human missions to the Moon. Similar antennas have been built in recent years in Canberra, while two are under construction in Madrid.
The DSN, the world’s largest and busiest deep space network, is clustered in three locations — Goldstone, California; Madrid, Spain; and Canberra, Australia — that are positioned approximately 120° apart around the globe to enable continual contact with spacecraft as the Earth rotates.
“The DSN is Earth’s one phone line to our two Voyager spacecraft — both in interstellar space — all our Mars missions, and the New Horizons spacecraft that is now far past Pluto,” said JPL Deputy Director Larry James. “The more we explore, the more antennas we need to talk to all our missions.”
While DSS-23 will function as a radio antenna, it will also be equipped with mirrors and a special receiver for lasers beamed from distant spacecraft. This technology is critical for sending astronauts to places like Mars. Humans there will need to communicate with Earth more than NASA’s robotic explorers do, and a Mars base, with its life support systems and equipment, would buzz with data that needs to be continually monitored.
“Lasers can increase your data rate from Mars by about 10 times what you get from radio,” said Suzanne Dodd, director of the Interplanetary Network, the organization that manages the DSN. “Our hope is that providing a platform for optical communications will encourage other space explorers to experiment with lasers on future missions.”
While clouds can disrupt lasers, Goldstone’s clear desert skies make it an ideal location to serve as a laser receiver about 60% of the time. An upcoming demonstration of DSS-23’s capabilities is just around the corner: When NASA launches an orbiter called Psyche to a metallic asteroid in a few years, it will carry an experimental laser communications terminal developed by JPL. Called the Deep Space Optical Communications project, this equipment will send data and images to an observatory at Southern California’s Palomar Mountain. But Psyche will also be able to communicate with the new Goldstone antenna, paving the way for higher data rates in deep space.
The DSN is working at the edge of our solar system. Starting in the spring of this year, NASA’s Voyager 2 (which requires ~16 hours for its radio signal to reach Earth) will quietly coast through interstellar space without receiving commands from Earth. That’s because the Voyager’s primary means of communication, the DSN’s 70-meter-wide (230-feet-wide) radio antenna in Canberra, Australia, will be undergoing critical upgrades for about 11 months. During this time, the Voyager team will still be able to receive science data from Voyager 2 on its mission to explore the outermost edge of the Sun’s domain and beyond. In fact, Voyager 2 proved to be among the DSN’s bigger challenges, when the communications teams had to predict exactly which frequencies the spacecraft’s antenna was receiving on after its capacitors failed mid-way to Jupiter.
About the size of a 20-story office building, the dish in Canberra has been in service for 48 years. Some parts of the 70-meter antenna, including the transmitters that send commands to various spacecraft, are 40 years old and increasingly unreliable. The DSN upgrades are planned to start now that Voyager 2 has returned to normal operations, after accidentally overdrawing its power supply and automatically turning off its science instruments in January.
The DSN operates 24 hours a day, 365 days a year. Its three sites around the world allow navigators to communicate with spacecraft at the Moon and beyond at all times during Earth’s rotation. Voyager 2, which launched in 1977, is currently more than 17 billion kilometers (11 billion miles) from Earth. It is flying in a downward direction relative to Earth’s orbital plane, where it can be seen only from the southern hemisphere and thus can communicate only with the Australian site.
Moreover, a special S-band transmitter is required to send commands to Voyager 2 — one both powerful enough to reach interstellar space and on a frequency that can communicate with Voyager’s 1970s technology. The Canberra 70-meter antenna (called “DSS43”) is the only such antenna in the southern hemisphere. As the equipment in the antenna ages, the risk of unplanned outages will increase, which adds more risk to the Voyager mission. The planned upgrades will not only reduce that risk, but will also add state-of-the art technology upgrades that will benefit future missions. “Obviously, the 11 months of repairs puts more constraints on the other DSN sites,” said Jeff Berner, Deep Space Network’s chief engineer. “But the advantage is that when we come back, the Canberra antenna will be much more reliable.”
The repairs will benefit far more than Voyager 2, including future missions like the Mars 2020 rover and Moon-to-Mars exploration efforts. The network will play a critical role in ensuring communication and navigation support for both the precursor Moon and Mars missions and the crewed Artemis missions. “The maintenance is needed to support the missions that NASA is developing and launching in the future, as well as supporting the missions that are operating right now,” said Suzanne Dodd, Voyager project manager and JPL Director for the Interplanetary Network.
The three Canberra 34-meter antennas can be configured to listen to Voyager 2’s signal; they just won’t be able to transmit commands. In the meantime, said Dodd, the Voyager team will put the spacecraft into a quiescent state, which will still allow it to send back science data during the 11-month downtime.
“We put the spacecraft back into a state where it will be just fine, assuming that everything goes normally with it during the time that the antenna is down,” said Dodd. “If things don’t go normally — which is always a possibility, especially with an aging spacecraft — then the onboard fault protection that’s there can handle the situation.” Berner says the work on the 70-meter antenna is like bringing an old car into the shop: There’s never a good time to do it, but it will make the car much more dependable if you do. The work on the Canberra DSN station is expected to be completed by January 2021.
In the meantime, anyone can monitor what is happening at the three main DSN sites via the “DSN Now” website. This site lists in graphical mode which antenna are transmitting to which spacecraft. So if you are interested in finding out when the next packet of images from Mars or the Kuiper belt are being sent back, you can watch it all live at https://eyes.nasa.gov/dsn/dsn.html.
The DSN is managed by JPL for NASA’s Human Exploration and Operations’ Space Communication and Navigation program. For more information on the first 40 years of the DSN, visit https://history.nasa.gov/SP-4227/Uplink-Downlink.pdf.