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NASA's Deep Space Network...
Communicating With Interplanetary Spacecraft
sites | other uses | map | history | ground equipment | uplinks downlinks | weak signals | tracking | voyagers | jpl | more


NASA photo of sheep flocking around Deep Space Network antenna at Madrid, Spain
Sheep flock grazes near NASA's
Deep Space Network antenna at Madrid
[click to enlarge NASA photo]
 
NASA photo of Deep Space Network antenna trio at Canberra, Australia
Three antennas at Canberra
[click to enlarge NASA photo]
 
NASA photo of Deep Space Network antenna at Goldstone, California
Goldstone antenna at twilight
[click to enlarge NASA photo]
 
NASA photo of Deep Space Network antenna at Madrid, Spain
Madrid Deep Space Network antenna
[click to enlarge NASA photo]
 
NASA photo of Deep Space Network antenna at Canberra, Australia
Canberra Deep Space Network antenna
[click to enlarge NASA photo]
 
NASA photo of Deep Space Network antenna at Goldstone, California
Goldstone Deep Space Network antenna
[click to enlarge NASA photo]
NASA's Deep Space Network (DSN) is a collection of antennas at three sites around the globe used to communicate with interplanetary spacecraft missions.

DSN also is used by radio and radar astronomers to observe the Solar System and the Universe.

The international network also supports selected Earth-orbiting missions.

There are three deep-space such communications facilities placed approximately 120 degrees apart around the world: That combination of locations permits constant observation of spacecraft as the Earth rotates, and helps to make DSN the largest and most sensitive scientific telecommunications system in the world. Each location has an 8-hour to 14-hour viewing period for contact with a spacecraft.

The complexes are far from heavily populated areas so that the very weak signals from distant spacecraft are not contaminated or obscured by radio interference from electrical power lines, radio and television stations, or household and industrial appliances.

Interplanetary probes. When NASA sends unmanned automated spacecraft to carry out its program of scientific investigation of the Solar System, DSN provides the two-way communications link that guides and controls those robot explorers, and receives the images and science data they send back.

The highly sophisticated autonomous explorers flying across the Solar System have sent back surprising information about our planetary neighbors Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto has yet to be visited.

All of the DSN antennas are large "dish" antennas — steerable, high-gain, parabolic reflectors — used to: Radio signals transmitted from DSN antennas control an interplanetary probe's operating modes, loading and reprogramming its computers, navigating it to its destination, and causing it to send scientific data back to Earth at certain times.

Other uses. The DSN antennas also are used for radar observations of bodies in the Solar System and for radioastronomy observations of the Universe.

For instance, the DSN provides planetary and solar scientists with radio data about changes in a radio signal as a spacecraft passes through a planet's atmosphere or the Sun's corona. Scientists interpret such data to better understand planetary atmosphere and the solar wind.

In addition, some satellites orbiting very high above Earth, and some low-orbit spacecraft, communicate through the DSN.

There is a big difference in communicating over a billion miles to an interplanetary probe and over distances of 100 miles to 23,000 miles.

The small 85-ft. antennas at each complex are used for communicating with satellites orbiting near Earth. Signals from such nearby spacecraft are strong and don't require the larger diameter antennas and ultrasensitive low-noise receivers used for deep space missions. However, tracking is important and the antennas must be able to follow objects moving across the sky at high speed and in view of an antenna for only 10 to 12 minutes.

NASA world map of Deep Space Network antenna sites
Click to enlarge NASA world map of Deep Space Network antenna sites
Never ending chatter. Every American deep space mission sees continuous radio communication between Earth and the spacecraft. With a variety of probes flying across the Solar System at any time, maintaining that "24/7" communications coverage with each requires the use of multiple stations back home on Earth at locations that compensate for Earth's daily rotation.

DSN's locations in California, Australia and Spain, Australia are approximately 120 degrees apart in longitude, which enables continuous overlapping reception of multiple spacecraft radio links.

Each complex is situated in a semi-mountainous, bowl-shaped terrain to shield against radio frequency interference from neighboring areas on Earth's surface.

Their locations:

How it all began. The first U.S. satellite successfully launched to orbit was the U.S. Army's Explorer-1 in January 1958.

Explorer 1 was designed and built by JPL, under contract to the U.S. Army. To track that launch and the satellite in space, the forerunner of the Deep Space Network was established.

JPL set up portable radio tracking stations in Nigeria, Singapore, and California to receive telemetry and plot the orbit of Explorer 1.

Later that year, the National Aeronautics and Space Administration (NASA) was established on October 1 to consolidate the separate Army, Navy, and Air Force space exploration programs under one civilian organization.

On December 3, 1958, JPL was transferred from the Army to NASA and given responsibility for building and flying lunar and planetary explorations with robot spacecraft.

Shortly afterward, NASA established the Deep Space Network to provide communications for all deep space missions, thereby avoiding the need for each project to build its own space communications network.

In the course of developing and operating communications equipment for all interplanetary probes, DSN became a world leader in the development of low-noise receivers; tracking, telemetry and command systems; digital signal processing; and deep space navigation.

DSN's initial complex was at Goldstone. The site's first 85-ft. antenna was named Pioneer after the first spacecraft with which it communicated, Pioneer 3 and Pioneer 4 in December 1958 and March 1959

None of the American planetary exploration missions of discovery would have been possible were it not for Deep Space Network radio communications.


Ground equipment. Each site has at least four deep space receiving and transmitting stations equipped with ultrasensitive receivers and large parabolic dish antennas.

Each complex has a: Five of those 111-ft. beam waveguide antennas were added to the sites at the end of the 1990's — three at Goldstone and one each at Madrid and Canberra. Because of a growing demand for DSN services, another antenna was under construction at Madrid. [construction photos]

Other equipment. All the receiving and transmitting stations are operated remotely from a central signal processing center at each site. Those processing centers have electronic systems that point and control the antennas, receive and process telemetry data, transmit commands, and generate spacecraft navigation data.

For example, to pick up, at the same time, communications from a spacecraft such as Galileo, the 230-ft. antenna at Goldstone can linked electronically to an identical antenna located in Australia, and to the 111-ft. antennas at Canberra.

Once incoming data is processed, it is transmitted to JPL at Pasadena, California, for further processing and distribution to scientists.


Uplinks and downlinks. Signals sent out from Earth to a spacecraft are referred to as "uplink." Signals received on Earth from a distant spacecraft are called "downlink."

A two-way communications link between Earth and a spacecraft includes these kinds of data: For high-power uplink transmissions, the 230-ft.-diameter antennas are equipped with transmitters that deliver up to 400 kilowatts of power.

Microwave radio. Three radio frequency bands are used on Earth for point-to-point communication: Microwave radio is used for deep space communications.

A microwave beam travels in a straight line. It can be reflected from a smooth surface and it can be focused by a lens or a curved reflector to increase its strength, or brightness.

As microwave frequencies increase, more signal from a spacecraft hits the antenna reflector on Earth because the transmitted radio beam is narrower — it has a tighter focus when pointed at Earth.

The result is a stronger signal received and a weaker noise level. For this reason, NASA is developing communications at ever higher frequencies for future use.

Weak signals. Radio signals weaken as they travel from a deep space probe across the great distance to Earth. Receiving antennas on Earth must have greater reflecting surface to pick up the weak signals.

As a spacecraft travels outward from Earth, its signal steadily decreases in power so that by the time it returns to a DSN antenna on Earth from a planetary encounter, it can be of extremely low wattage.

SIGNAL TO NOISE RATIO
The signal-to-noise ratio of an antenna and receiver is a measure of the receiving station's ability to distinguish a probe's signal in the midst of unwanted noise. A strong signal-to-noise ratio can make a critical difference in data received.
It may be 20 billion times weaker than the power required for a digital wristwatch. It could be about 1,000 billion times weaker than the signal received by a TV set from a commercial television station.

As the signal from a distant probe enters an antenna on Earth, the signal is degraded by background radio noise, or static. Such noise is radiated naturally by all objects in the Universe, including Earth and the Sun. Unfortunately, noise is amplified along with the probe's signal.

To reduce the effect of noise, engineers on Earth design receiving systems with noise-combating telemetry coding techniques, high signal sensitivity, efficient antennas, and low-noise receivers.

Unfortunately for scientific communication, microwave radio also is used on Earth by television stations, cellular telephone towers, data communication networks, radar, FM radio broadcasts, and transmissions to and from Earth-orbiting satellites. Such other signals, transmitted nearby on adjacent frequencies, have the potential to interfere with reception of weak signals from deep space.

Tracking probes. The antennas on Earth must be able to track at very precise rates — at thousandths of a degree per second — to remain pointed at the spacecraft as the Earth is rotating at 0.004 degrees per second.

The distant spacecraft stay within the view of a single DSN station for lengths of time from 10 to 12 hours.

Precision pointing of a deep-space antenna is critical. An antenna can see only a small portion of the sky and must be pointed directly at a spacecraft, whether receiving data or transmitting commands. Imagine looking at the sky through a soda straw.


Voyagers and DSN. In 2002, the Deep Space Network engineers celebrated 25 years of two-way communication with the Voyager-1 and Voyager-2 spacecraft, which today are exploring the far outer reaches of the Solar System.

Both Voyagers are so far away from Earth that only the largest DSN antennas — 230 feet in diameter — can send commands to the spacecraft. To do that, they use of a 20 kilowatt S-Band transmitter. That's about one-half to one-quarter of the power transmitted by an ordinary commercial AM or FM radio station on Earth.

The commands transmitted tell the Voyagers when to gather data and when to transmit that information back to Earth. The commands travel across millions of miles of space are on very weak when they arrive at the spacecraft.

On average, the stations track the very distant pair of robot probes about 12 hours a day.

A command signal, traveling at the speed of light, takes almost 12 hours to reach Voyager-1.

Voyager 2 isn't quite as far away. A command transmitted to Voyager-2 only takes only about 10 hours to reach the spacecraft.

By comparison, a signal sent to Mars, to command the Mars Global Surveyor spacecraft, takes only 15 minutes.

Successfully sending a DSN signal into Voyager-2's receiver is like throwing a baseball across thousands of miles of ocean into a porthole of a moving cruise ship.

In the future, as the Voyagers move even farther away from Earth, DSN engineers will invent new techniques to communicate with them.


Jet Propulsion Laboratory. DSN is part of NASA's Space Operations Management Office (SOMO). The Interplanetary Network Directorate (IND) at NASA's Jet Propulsion Laboratory (JPL) manages DSN. JPL is a division of the California Institute of Technology (Caltech) at Pasadena, California.

The three international DSN complexes are controlled by the Network Operations Control Team (NOCT) at JPL's Deep Space Operations Center. Voice and data communications circuits that link the complexes to NOCT and to flight operation centers around the world are managed and operated by DSN's Ground Communications and Information Service.


Learn more about the Deep Space Network:
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