Deep Space Network: The interplanetary WiFi

Locations of the Deep Space Network stations

(Image credits: NASA)

Deep Space Network or DSN is a collection of big radio antennas that track, command, and monitor spacecraft and satellites. DSN acts like a mediator between us and satellites that are sent for missions to obtain data from space. DSN keeps in touch with almost all satellites (Earth-orbit satellite) as well as spacecraft. DSN is the largest and most sensitive scientific telecommunications system in the world. Many countries like India, Japan, China own a personal deep space network but globally we have NASA’s Deep Space Network as common.

Deep Space Network was established under Jet Propulsion Laboratory (JPL), a federally funded research and development center and NASA field center located in Pasadena, California. It is managed by the California Institute of Technology (Caltech) for NASA. The JPL was essentially used by the U.S army as a portable radio tracking station in 1958. Later the same year, it was transferred to NASA, to design as well as to execute lunar and planetary exploration programs using robotic spacecraft. 

It consists of three radio antennas (complexes) positioned equidistant from each other around the world – approx 120 degrees apart in longitude. These sites are located at Goldstone, near Barstow, California; near Madrid, Spain; and near Canberra, Australia. The largest antenna at each DSN site is 70 meters (230 feet) in diameter. 

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. 

These are placed on semi-mountainous or on bowl-shaped terrain to help shield against radio frequency interference. Due to the rotation of earth, communication between DSN and satellites does not stop as a distant spacecraft sinks below the horizon at one DSN site, another site can pick up the signal and carry on communication.

These antennas are driven by a 200 horsepower motor that is equivalent to the power of a car engine and  can communicate in both uplink (DSN to satellite) and downlink (satellite to DSN) in S, X, K and Ka-band radio signals, which are different types of radio communication.

Therefore, DSN is a backbone for interplanetary missions and a few that orbit Earth. It provides radar and radio astronomy observations that improve our understanding of the solar system and the larger universe.

How does DSN work?

Operators at DSN command antennas by breaking them into digital bits. They precisely aim antennas at spacecraft and send the command. The antennas must point very accurately towards the spacecraft, because an antenna can see only a tiny portion of the sky. The command is sent as radio waves. The spacecraft receives the signal and executes the command. The spacecraft collects scientific data and images. These data are then sent back to Earth as digital bits which are again collected by antennas and then are accessible to scientists of the Space Flight Operations Facility at the Jet Propulsion Laboratory. There, the photos and other data are processed and shared with scientists and with the rest of the world.

DSN Missions

DSN has been part of Apollo missions and is currently part of every interplanetary mission. The far distant objects that the DSN communicates with, are NASA’s two Voyager spacecrafts. Launched in 1977, Voyagers 1 and 2 studied Jupiter, Saturn, Uranus and Neptune. Today, Voyager 1 is exploring beyond our solar system in interstellar space.

image credit: General dynamics

Because the Voyagers are so far away, their signals to the antennas are very weak. In fact, the power that theDSN antennas receive from the Voyager signals is 20 billion times weaker than what is needed to run adigital watch. Engineers have figured out ways to boost those signals so they can be “heard” loud and clear.

Antennas

Antennas are equipped with amplifiers to hear faint signals but there are few problems. First, the signal

becomes degraded by background radio noise, or static, emitted naturally by nearly all objects in the

universe, like the sun and earth. The background noise gets amplified along with the signal. Second,

the powerful electronic equipment amplifying the signal adds noise of its own. To compensate, 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.

DSN challenges

Major challenges are in transmission as data transmission rates from/to spacecraft and space probes are severely constrained due to the distances from Earth. Another challenge is life-time of antennas, as they are reaching their limit of service and replacement of components can put the system out of service for months. 

IDSN

India owns its personal DSN which is controlled by Indian Space Research Organization (ISRO) to support its interplanetary spacecraft missions. The IDSN was launched on 17th Oct 2008. The IDSN has three antennas located at three different sites in India, namely at Byalalu, Karnataka; Sriharikota,

Andhra Pradesh; and Bearslake, Jharkhand.

Indian Deep Space Network

(Image credits: India Strategic)

The main antenna is a 32m deep space antenna. It supported the Chandrayaan mission and Mars Orbiter

Mission (MOM). The antenna provides uplink in both S-band (20/2 kW) and X-band(2.5 kW). The second

antenna is a 18m antenna. It is capable of performing both uplink and downlink in both S-band and X-band.

And the third antenna is a 11m S/X band antenna that has been established for AstroSat missions

(missions aiming at studying celestial sources in X-ray, optical and UV spectral bands).

The three antennas of the IDSN provide a robust and reliable network for communicating with deep

space missions, which is essential for space exploration and scientific discovery.

Overall, the global NASA Deep Space Network has a 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. Without DSN there would be no missions, It has become an interplanetary Wi-Fi.