Deep Space Network

From Wikipedia, the free encyclopedia

Deep Space Network

Organization

Interplanetary Network Directorate

Coordinates

Website
http://deepspace.jpl.nasa.gov/dsn/

Telescopes
Goldstone Deep Space Communications Complex	near Barstow, California
Robledo de Chavela	near Madrid, Spain
Canberra Deep Space Communications Complex	near Canberra, Australia

DSN logo

The Deep Space Network, or DSN, is an international network of communication facilities that supports interplanetary spacecraft missions, and radio and radar astronomy observations for the exploration of the solar system and the universe. It is best known for its large radio antennas. The network also supports selected Earth-orbiting missions. DSN is part of the NASA Jet Propulsion Laboratory (JPL).

1 History
2 General information
3 Antennas
4 Network limitations and challenges
5 See also
6 References
7 External links and further reading

[edit] History

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 to receive telemetry and plot the orbit of the Army-launched Explorer 1, the first successful U.S. satellite.^[1] NASA was officially established on October 1, 1958, to consolidate the separately developing space-exploration programs of the Army, Navy, and Air Force into one civilian organization^[2].

On 3 December 1958, the JPL was transferred from the Army to NASA and given responsibility for the design and execution of lunar and planetary exploration programs using remotely-controlled spacecraft. The Deep Space Network (DSN) also provided the communications and tracking for all of the manned Apollo missions to the Moon.

Shortly after the transfer of the JPL to NASA, NASA established the concept of the Deep Space Network as a separately managed and operated communications system that would accommodate all deep space missions, thereby avoiding 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 operation in support of all of its users. Under this concept, it has become a world leader in the development of low-noise receivers; large parabolic-dish antennas; tracking, telemetry, and command systems; digital signal processing; and deep space navigation.

The largest antennas of the DSN are often called on during spacecraft emergencies. Almost all spacecraft are designed so normal operation can be conducted on the smaller (and more economical) antennas of the DSN, but during an emergency the use of the largest antennas is crucial. This is because a troubled spacecraft may be forced to use less than its normal transmitter power, attitude control problems may preclude the use of high-gain antennas, and recovering every bit of telemetry is critical to assessing the health of the spacecraft and planning the recovery. The most famous example is the Apollo 13 mission, where limited battery power and inability to use the spacecraft's high gain antennas reduced signal levels below the capability of the Apollo Network, and the use of the biggest DSN antennas (and the Australian Parkes Observatory radio telescope) was critical to saving the lives of the astronauts. Although in this case Apollo was also a USA/NASA mission, DSN also provides this same emergency service to other space agencies as well, in a spirit of inter-agency and international cooperation. For example, the recovery of the Solar and Heliospheric Observatory (SOHO) mission of the European Space Agency (ESA) would not have been possible without the use of the largest DSN facilities.

[edit] General information

Deep Space Network Operations Center

DSN currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world^[3]. They are:

the Goldstone Deep Space Communications Complex outside of Barstow, California, United States;
the Madrid Deep Space Communication Complex, 60 kilometers (37 miles) west of Madrid, Spain; and
the Canberra Deep Space Communications Complex (CDSCC) in the Australian Capital Territory, 40 kilometers (25 miles) southwest of Canberra, Australia near the Tidbinbilla Nature Reserve.

Each facility is situated in semi-mountainous, bowl-shaped terrain to shield against radio frequency interference. This strategic placement permits constant observation of spacecraft as the Earth rotates, and helps to make the DSN the largest and most sensitive scientific telecommunications system in the world.

NASA's scientific investigation of the Solar System is being accomplished mainly through the use of unmanned spacecraft. The DSN provides the vital two-way communications link that guides and controls these planetary explorers, and brings back the images and new scientific information they collect. All DSN antennas are steerable, high-gain, parabolic reflector antennas.

The antennas and data delivery systems make it possible to:

Acquire telemetry data from spacecraft.
Transmit commands to spacecraft.
Track spacecraft position and velocity.
Perform Very Long Baseline Interferometry observations.
Measure variations in radio waves for radio science experiments.
Gather science data.
Monitor and control the performance of the network.

The network is a facility of the JPL and is managed and operated for NASA by the California Institute of Technology (Caltech). The Interplanetary Network Directorate (IND) manages the program within JPL.

[edit] Antennas

70m antenna at Goldstone

Each complex consists of at least four deep space terminals equipped with ultra-sensitive receiving systems and large parabolic-dish antennas. There are:

One 34-meter (111-ft) diameter High Efficiency antenna.
One or more 34-meter Beam Waveguide antennas (three at the Goldstone Complex, two at the Robledo de Chavela complex (near Madrid), and one at the Canberra Complex).
One 26-meter (85-foot) antenna.
One 70-meter (230-foot) antenna.

Five of the 34-meter beam waveguide antennas were added to the system in the late 1990s. Three were located at Goldstone, and one each at Canberra and Madrid. A second 34-meter beam waveguide antenna (the network's sixth) was completed at the Madrid complex in 2004.

The ability to array several antennas was incorporated to improve the data returned from the Voyager 2 Neptune encounter, and extensively used for the Galileo spacecraft, when the high gain antenna did not deploy correctly^[4]. The array electronically links the 70-meter dish antenna at the Deep Space Network complex in Goldstone, California, with an identical antenna located in Australia, in addition to two 34-meter (111-foot) antennas at the Canberra complex. The California and Australia sites were used concurrently to pick up communications with Galileo.

Arraying of antennas within the three DSN locations is also used. For example, a 70-meter dish antenna can be arrayed with a 34-meter dish. For especially-vital missions, like Voyager 2, the Canberra 70-meter dish can be arrayed with the Parkes Radio Telescope in Australia; and the Goldstone 70-meter dish can be arrayed with the Very Large Array of antennas in New Mexico. Also, two or more 34-meter dishes at one DSN location are commonly arrayed together.

All the stations are remotely operated from a centralized Signal Processing Center at each complex. These Centers house the electronic subsystems that point and control the antennas, receive and process the telemetry data, transmit commands, and generate the spacecraft navigation data.

Once the data is processed at the complexes, it is transmitted to JPL for further processing and for distribution to science teams over a modern communications network, frequently using satellite communications.

[edit] Network limitations and challenges

70m antenna in Madrid, Spain

There are a number of limitations to the current DSN, and a number of challenges going forward.

There is only one DSN site in the Southern Hemisphere, Canberra. There are no DSN network dishes in South America or Southern Africa, so the DSN coverage of the Southern Hemisphere is limited.

The need to support "legacy" missions that have remained operational beyond their original lifetimes but are still returning scientific data. Programs such as Voyager have been operating long past their original mission termination date. They also need some of the largest antennas.

The DSN's deferred maintenance of its 70m antennas. This causes problems where they are out of service for months at a time. Furthermore, they are reaching the end of their lives. At some point they will need to be replaced. The leading candidate is an array of smaller dishes^[5]^[6].

By 2020, the DSN will be required to support twice the number of missions it was supporting in 2005.

[edit] See also

Extended NASA missions

Notes

Ulysses' mission has been extended until March 2009. The craft will continue operating while flying over the Sun's poles for the third time sometime in 2007-2008. At some point in time the craft's RTG will not provide enough power to operate the craft's science instruments. Current orbital parameters will keep the hydrazine fuel from freezing.
The two Voyager spacecraft continue to operate, with some loss in subsystem redundancy, but retain the capability of returning science data from a full complement of VIM science instruments. Both spacecraft also have adequate electrical power and attitude control propellant to continue operating until around 2020, when the available electrical power will no longer support science instrument operation. At this time, science data return and spacecraft operations will cease.