Discover

The 'Deep Space Network', or 'DSN', is an international 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).

Contents

History

General information

Antennas

Network limitations and challenges

Southern Hemisphere coverage issues

Other weaknesses

Future problems

See also

References

External links and further reading

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. 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.
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 automatically operated spacecraft. Shortly afterwards, NASA established the concept of the Deep Space Network as a separately managed and operated communications facility 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 Deep Space Network 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; 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. Although almost all spacecraft are designed so normal operation can be conducted on smaller (and more economical) antennas, during an emergency the use of the largest antennas is critical. This is because troubled spacecraft may be forced to use less than their 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 Parkes Observatory radio telescope, called in for this emergency) 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.

General information

DSN currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world at:

★ the Goldstone Deep Space Communications Complex outside of Barstow, California, United States;

★ the Madrid Deep Space Communication Complex, 60 kilometres (37 miles) west of Madrid, Spain; and

★ the Canberra Deep Space Communications Complex (CDSCC) in the Australian Capital Territory, 40 kilometres (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.

Antennas

Each complex consists of at least four deep space stations equipped with ultrasensitive receiving systems and large parabolic dish antennas. There are:

★ One 34-metre (111-ft) diameter High Efficiency antenna.

★ One or more 34-metre 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-metre (85-foot) antenna.

★ One 70-metre (230-foot) antenna.
Five of the 34-metre 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-metre 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 Galileo spacecraft. The array electronically links the 70-metre antenna at the Deep Space Network complex in Goldstone, California, with an identical antenna located in Australia, in addition to two 34-metre (111-foot) antennas at the Canberra complex. The California and Australia sites were used concurrently to pick up communications with Galileo.
All the stations are remotely operated from a centralized Signal Processing Center at each complex. The 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 ground communications network.

Network limitations and challenges

Southern Hemisphere coverage issues

There is only one DSN site in the Southern Hemisphere, thus the DSN coverage of the Southern Hemisphere is limited, in spite of the Canberra complex.

★ There are no DSN network dishes in South America

★ There are no DSN network dishes in Southern Africa
If the DSN had full Southern Hemisphere redundancy of its Northern Hemisphere assets, weather and equipment related data loss events would occur less often.

Other weaknesses

DSN Mission data loss problems are not yet severe, however, ongoing problems clearly exist.
The Voyager program has been operating long past its original mission termination date. The Voyager craft are the only known NASA missions experiencing ongoing data loss events.
Possible reasons for ongoing Voyager data loss events

★ The Voyager craft data loss problems are mostly related to the lack of fully redundant 70m assets DSN in the Southern Hemisphere

★ The DSN's deferred maintenance of its 70m assets in the Northern Hemisphere has caused some data loss

★ The DSN 70m assets are not fully redundant in both hemispheres

Future problems

In addition, the DSN faces a number of foreseeable challenges over the next few years:

★ New mission support is always being added at the rate of ~350% over the last 20 years.

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

★ The need to balance "legacy" missions that have remained operational beyond their original lifetimes but are still returning scientific data

★ The older antennas, particularly the 70m dishes, are reaching the end of their lives. At some point they will need to be replaced.

See also

Extended NASA missions

★ Ulysses probe

★ Mars Exploration Rovers

★ Voyager program

★
★ Voyager 1

★
★ Voyager 2
Notes
# Ulysses' mission has been extended until March 2008. 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.
Related Sources and Topics

★ ESTRACK

★ List of observatories

★ List of radio telescopes

References

★ deepspace.jpl.nasa.gov/dsn - ABOUT THE DEEP SPACE NETWORK

External links and further reading

★ NASA/Caltech JPL DSN - official site.

★ (PDF) ''Uplink-Downlink: A History of the Deep Space Network, 1957-1997'' (NASA SP-2001-4227).

★ Douglas J. Mudgway, ''Big Dish: Building America's Deep Space Connection to the Planets'', University of Florida Press, 2005 ISBN 0-8130-2805-1.

★ (PDF) April 2006 GAO report ''NASA's Deep Space Network: Current Management Structure Is Not Conducive to Effectively Matching Resources with Future Requirements''

★ An Early NASA Pioneer Still on the Job in Deep Space