|
|
|
|
Deep Space Network
|
| |
|
| |
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.
Discussion
Ask a question about 'Deep Space Network' Start a new discussion about 'Deep Space Network' Answer questions from other users |
Encyclopedia
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).
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 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.
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 Manned Space Flight 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.
General information
DSN currently consists of three deep-space communications facilities placed approximately 120 degrees apart around the world. They are:
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 machines, 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 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 ft) antenna.
- One 70-meter (230 ft) 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. 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 ft) 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.
DSN and the Apollo program
Although normally tasked with tracking unmanned spacecraft, the Deep Space Network (DSN) also contributed to the communication and tracking of Apollo missions to the Moon, although primary responsibility was held by the Manned Space Flight Network. The DSN designed the MSFN stations for lunar communication and provided a second antenna at each MSFN site (the MSFN sites were near the DSN sites for just this reason). Two antennas at each site were needed both for redundancy and because the beam widths of the large antennas needed were too small to encompass both the lunar orbiter and the lander at the same time. DSN also supplied some larger antennas as needed, in particular for television broadcasts from the Moon, and emergency communications such as Apollo 13.
From a NASA report describing how the DSN and MSFN cooperated for Apollo:
Another critical step in the
evolution of the Apollo Network came in 1965 with the advent
of the DSN Wing concept. Originally, the participation of
DSN 26-m antennas during an Apollo Mission was to be limited
to a backup role. This was one reason why the MSFN 26-m
sites were collocated with the DSN sites at Goldstone, Madrid,
and Canberra. However, the presence of two, well-separated
spacecraft during lunar operations stimulated the rethinking
of the tracking and communication problem. One thought was
to add a dual S-band RF system to each of the three 26-m
MSGN antennas, leaving the nearby DSN 26-m antennas still in
a backup role. Calculations showed, though, that a 26-m
antenna pattern centered on the landed Lunar Module would
suffer a 9-to-12 db loss at the lunar horizon, making tracking
and data acquisition of the orbiting Command Service
Module difficult, perhaps impossible. It made sense to
use both the MSFN and DSN antennas simultaneously during the
all-important lunar operations. JPL was naturally reluctant
to compromise the objectives of its many unmanned spacecraft
by turning three of its DSN stations over to the MSFN for
long periods. How could the goals of both Apollo and deep
space exploration be achieved without building a third 26-m
antenna at each of the three sites or undercutting planetary
science missions?
The solution came in early 1965 at a meeting at NASA
Headquarters, when Eberhardt Rechtin suggested what is now
known as the "wing concept". The wing approach involves
constructing a new section or "wing" to the main building at
each of the three involved DSN sites. The wing would include
a MSFN control room and the necessary interface equipment
to accomplish the following:
i. Permit tracking and two-way data transfer with either
spacecraft during lunar operations.
2. Permit tracking and two-way data transfer with the
combined spacecraft during the flight to the Moon
3. Provide backup for the collocated MSFN site passive
track (spacecraft to ground RF links) of the Apollo
spacecraft during trans-lunar and trans-earth phases.
With this arrangement, the DSN station could be quickly
switched from a deep-space mission to Apollo and back again.
GSFC personnel would operate the MSFN equipment completely
independently of DSN personnel. Deep space missions would
not be compromised nearly as much as if the entire station's
equipment and personnel were turned over to Apollo for several
weeks.
Network limitations and challenges
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.
- By 2020, the DSN will be required to support twice the number of missions it was supporting in 2005.
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.
Related Sources and Topics
External links and further reading
- - official site.
- - a series of books published by Wiley detailing specifics on the Deep Space Network, JPL's site on , * Douglas J. Mudgway, Big Dish: Building America's Deep Space Connection to the Planets, University of Florida Press, 2005 ISBN 0-8130-2805-1.
-
-
- , on ESA Spacecraft Operations site; retrieved 19 October 2007
|
| |
|
|
