Deep Space Network

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DSN antenna system from Madrid

The Deep Space Network ( DSN ) is a global network of parabolic antennas that are used for communication with predominantly interplanetary space probes and satellites as well as for radio and radar astronomical research purposes.

DSN is part of a larger network and uses the capabilities of the terrestrial communications network provided by the NASA Integrated Services Network ( NISN ). The NISN enables the exchange of data at high speed with the other two networks and the missions. The other two networks are the Space Network , which works with geostationary relay satellites ( TDRS ) as receivers. B. to Guam Remote Ground Terminal (GRGT) and the Near Earth Network , which enables communication with missions during the launch phase in near-earth orbits and with near-earth satellites with many small and medium-sized antennas. Antennas from commercial satellite operators and other space agencies are also integrated into this network.

The first major tasks for NASA's deep space stations were communication with interplanetary space probes such as the Mariner and Pioneer programs, as well as Voyager 1 and Voyager 2 .

Three deep space complexes

Goldstone Madrid Canberra

Deep Space Network locations

The Jet Propulsion Laboratory currently operates two large stations in Goldstone and Madrid for the US space agency NASA . The Canberra station is managed by CSIRO on behalf of NASA .

117 ° W, 35 ° N		Goldstone Deep Space Communications Complex (GDSCC)
		Mojave Desert , California , USA
004 ° W, 40 ° N		Madrid Deep Space Communications Complex (MDSCC)
		Robledo de Chavela near Madrid , Spain
149 ° E, 35 ° S		Canberra Deep Space Communication Complex (CDSCC)
		Tidbinbilla near Canberra , Australia

Initially there were two other large stations with 26 m antennas:

• Woomera , Australia (1959–1972)
• Hartebeesthoek near Johannesburg , South Africa (1961–1974)

In addition, the DSN can still access the capabilities of the Launch Support Facility (MIL-71) in Florida during the launch phase at the Kennedy Space Center .

All three complexes are located in hilly terrain in a hollow to minimize interference from terrestrial radio frequencies. The strategic placement enables continuous communication with spacecraft close to the ecliptic, despite the rotation of the earth, because the stations are fairly evenly distributed (94 °, 113 ° and 153 °) over the longitudes of the earth. Before an object disappears behind the horizon, the next system can continue communication.

Additional antennas can be added in certain situations. The Parkes radio telescope can be integrated into the Canberra complex, and the combined signals from the 27 antennas of the Very Large Array (VLA) in New Mexico can be added to the Goldstone complex. This interconnection technique was used for the Voyager missions and Pioneer 11's flybys of Jupiter, Saturn, Uranus and Neptune. Later, the Gallileo mission relied on this technology again to mitigate the consequences of the failed main antenna.

history

The forerunner of the Deep Space Network (DSN) was founded in January 1958 when the Jet Propulsion Laboratory (JPL), then under contract with the US Army , deployed mobile tracking ground stations in Nigeria , Singapore and California to obtain telemetry data from the Explorer launched by the Army 1 , the first successful satellite in the United States, and track its trajectory. NASA was officially founded on October 1, 1958 to merge the differently evolving space programs of the US Army, the US Navy and the US Air Force in a civilian organization.

On December 3, 1958, the JPL was transferred from the US Army to NASA and was given responsibility for the design and implementation of lunar and planetary exploration programs with remote-controlled spacecraft. Shortly thereafter, NASA introduced the Deep Space Network as a separately managed and operated communications system that would be available to all deep space missions. This avoids having to set up and operate a dedicated, specialized space communication network for each space project. The DSN was responsible for research, development and operations in order to support all of its users equally. Under this concept, it became a world leader in the development of low-noise receivers, large parabolic antennas , radio tracking, telemetry and command systems, digital signal processing and deep space navigation.

The Manned Space Flight Network (MSFN)

It all started with a network of 26 m antennas, which were originally located in more locations. The Manned Space Flight Network (MSFN) was a global antenna network that was specifically used for the manned space flight of the Mercury , Gemini , Apollo and Skylab programs. It required many antennas around the globe and was set up to maintain constant contact without interruptions to astronauts and spaceships in low-earth orbits. Objects in low orbits move quickly, so the antennas needed to have fast tracking capabilities and were therefore limited in size. These were:

• NRAO 85-1 Howard E. Tatel Radio Telescope in Green Bank , West Virginia since 1958. This 26 m antenna was later converted to the Green Bank interferometer .
• Michigan Radio Astronomy Observatory (UMRAO) in Michigan .
• DSIF 51 / DSS 51 in Hartebeesthoek, South Africa , near Johannesburg . Built in 1961 and rebuilt in 1964 for L-band and S-band operation. Decommissioned from NASA in 1974, the telescope was handed over to the South African Council for Scientific and Industrial Research (CSIR), which continued to operate it for NASA and made it the Hartebeesthoek Radio Astronomy Observatory (HartRAO).
• In 1960, the DSS41 was built in Woomera in Australia , in 1964 it was converted for L and S band and in 1972 it was closed and dismantled.

Expansion for the Apollo program

The Apollo missions required additional antennas. During the lunar stay, one antenna was needed for communication with the lunar module and another for the command module, additional requirements arose from the transmission of television images from the lunar surface, and redundant antennas should also be available in the event of a failure. Therefore, additional 26 m antennas of the MSFN were installed in the complexes of the DSN in Goldstone, Madrid and Canberra. A large part of the communication ran via the MSFN, the DSN provided additional capacities for the short time spent on the moon as well as redundancy. In 1966 the first 64-m antenna for emergency communications came in Goldstone, in 1973 Madrid and Canberra got their own 64-m antennas.

Expansion for the Voyager missions

The missions went further and further into the area of ​​the outer planets, e.g. B. the Voyager probes , so that more powerful antennas were necessary. The required capacities for Voyager 2 in the Uranus area could no longer be managed with the existing 64 m and 26 m antennas, so additional 34 m antennas were built in the 1980s and 1990s, existing 26 m antennas Antennas have been expanded or replaced to 34 m antennas. When Voyager 2 came to Neptune , the capabilities of the 64-meter antennas were no longer sufficient, so they had to be expanded to 70-m antennas. By interconnecting many antennas, including antennas that do not belong to the DSN, the required data rate could be achieved.

The largest antennas of the DSN are occasionally used by spacecraft in emergency situations. Almost all spacecraft are designed to use the smaller (and more economical) antennas of the DSN during normal operation. But in an emergency, the largest antennas are crucial. This is because a troubled spacecraft might be forced to use less transmit power, or problems with attitude control might prevent the use of high gain antennas . It is also important to receive telemetry data as completely as possible in order to determine the condition of the spacecraft and to plan the rescue. The most famous example was the Apollo 13 mission, in which the radio signals were so weak that the Manned Space Flight Network could no longer receive them due to limited battery power and the inability to use the antennas with high antenna gain. The use of the largest DSN antennas (and the radio telescope from the Parkes Observatory in Australia ) were crucial in saving the astronauts. Even if Apollo 13 was an American mission, the DSN also offers these emergency services to other space agencies in the spirit of international cooperation between the various space agencies.

As of 2019

All 26 m antennas and the 34 m antennas with HEF have now been deactivated in favor of modern 34 m beam wave guide antennas. Each station has three active 34 m and one 70 m antennas. Each of the three complexes also has an 11 m antenna that is used for VLBI .

The 70 m antenna of the Goldstone complex is also equipped with very powerful transmitters. This ability makes the antenna a powerful radar device that enables high-resolution radar images of asteroids and other celestial bodies in the solar system. A strong signal is sent with the 70 m antenna in the direction of the celestial body and large radio telescopes e.g. B. the DSN, Green Bank and Arecibo collect the reflections. Radar images can then be generated from the data and the distance and precise path data can be calculated.

All three complexes have a network-independent, uninterruptible emergency power supply with batteries and diesel generators. In the event of a power failure, the batteries keep the devices in operation until the diesel generators have started up. Diesel engines are suitable because they do not have spark plugs and therefore do not cause electromagnetic interference. One of the tasks of the DSN is the electronic processing of large amounts of data and the storage and archiving of all data for future scientific analysis. There is also a backup for the control system in case Goldstone or any of the other control centers fail for any reason. All three stations have Delta-DOR technology. If several spacecraft are close together in the sky and transmit in the same frequency range but with slightly different frequencies, one antenna can receive and process up to four different signals at the same time. Such conditions are given, for example, when several Mars missions are running simultaneously.

Until November 5, 2017, the observation times and transmission and reception capacities were centrally controlled around the clock from the Goldstone complex in California and each control center operated 24 hours a day. Each of the three centers has its own technical and scientific staff for operation and maintenance and can serve as a backup of the DSN. So it was decided that the control would change regularly between the three complexes in accordance with a follow-the-sun regulation. This means that each station has eight hours of control during the day, which it then passes on to the next station at a defined time, one hour overlapping between the two stations during the handover. In this way, the three-shift operation in Goldstone and in the other stations could largely be eliminated and the existing staff could work more effectively. This improved working conditions and reduced personnel costs at the same time.

DSN has long been working closely with ESA's ESTRACK network on many missions, and in 2007 a mutual support agreement was signed. In some cases, the three 34 m ESTRACK antennas are positioned more favorably than those of the DSN, and there are also cases in which a particularly large amount of data is generated or many objects have to be observed at the same time. For VLBI, the cooperation enables new baselines between the stations of both agencies and thus more precise measurements. All systems comply with the provisions of the CCSDS , so data exchange and cooperation between different networks is possible. In some cases the DSN also works with other space agencies and their deep space antenna networks, e.g. B. with the JAXA systems in Usuda and the ISRO systems in Byalalu.

Future expansion and laser communication

General technical progress always brings better technology with it, e.g. B. higher resolution cameras, but also more and more data and communication needs. The amount of data transported doubles approximately every ten years. For high data rates, higher frequencies are better, more and more missions are using Ka-band for the downlink, while the demand for S-band is decreasing.

The DSN is currently being expanded to meet future communication needs. In the future, all three stations should have at least four modern 34 m beam wave guide antennas in addition to a 70 m antenna. In the event of a failure of the 70 m antenna, these antennas can be combined and replace the large antenna with at least the same power in the downlink. The existing systems get additional receivers for additional and higher frequency bands, and at least one of the smaller antennas gets a more powerful 80 kW transmitter. In the Goldstone complex, one of the 34 m bowls in the central area with a diameter of 8 m will be provided with mirrors and a receiver in the optical area in order to create reception possibilities for communication with laser. The technology will be tested first, and after the test phase it is expected to be implemented in Goldstone. Laser technology enables much higher data rates, but is more easily influenced by the weather.

All 70 m antennas are now over 40 years old and show signs of wear and tear. Maintenance is becoming more and more complex with increasing costs, and at the same time the procurement of spare parts is becoming more and more difficult. The 70 m antennas are to be replaced in the long term by an array of four 34 m antennas, all four antennas have a receiver and at least one of the four has a transmitter with 80 kW transmission power. The operation of four small antennas is much more flexible, but also cheaper to maintain than the large antenna. Antennas can be combined as required. In 2025 , all three complexes are to have five beam wave guide antennas and the 70 m antennas can be taken out of service. The end of the Voyager missions is also expected at that time, and the need for the 70 m antennas will be reduced accordingly.

All 70-meter antennas are to be taken out of service for ten months in the next few years in order to carry out extensive refurbishments and extensions. The 20 kW S-band transmitters are to be replaced by 100 kW transmitters, and the 20 kW X-band transmitters are to be replaced by 80 kW, and the X-band is being expanded. The 400 kW transmitter from DSS-43 is made obsolete by the 100 kW transmitter. The new facilities will go into operation for DSS-43 from December 2020, DSS-63 from December 2022 and DSS-14 from December 2024.

tasks

The DSN has two different areas of responsibility. The first and most important is space program support, the second is scientific research. The focus is on space travel, scientific research can be carried out as long as capacity is left.

The primary tasks of the space program are telemetry, tracking, control and monitoring

• Telemetry: The DSN has the option of receiving, calculating and decoding telemetry data from space probes and objects in orbit and distributing them to the appropriate locations. Telemetry data consists of scientific and operational data that are modulated onto radio signals sent by the spaceship. The telemetry system can receive and process this data, forward it to the individual projects and can check whether the data obtained are free of errors.

• Radiometric tracking (tracking): The radio tracking system enables mutual communication between the ground station and the spacecraft. It can be used to determine the position, speed and direction. All complexes have technology for the Delta-DOR method for precise orbit determination.
• Command transmission: The DSN ensures that the projects can transmit commands and course data to the spacecraft at the appropriate time. The DSN works as an intermediary between the projects and their property. In many cases, the communication times and the data transmitted can be planned in advance and processed without the direct involvement of the projects. The Advanced Multimission Operations System is used to fulfill this task , which assigns the necessary resources to the individual missions at the appropriate times. The individual projects can concentrate entirely on evaluating the mission data, while the DNS takes over the control and steering of the spacecraft.
• Monitoring and control: The task of the control and monitor system is to forward the data obtained to the projects in real time. It also maintains and monitors the function and operation of the DSN network.

There are a variety of scientific tasks that can often be performed in conjunction with other radio telescopes.

• Scientific antenna research: In addition to communication tasks, the DSN can also be used for space research and development. The possibilities can be used by all qualified scientists as long as the space programs are not impaired. It works with NASA and non-NASA observatories. The DSN continuously maintains and improves the scientific possibilities and takes on innovations, so that not only the current observations and experiments are supported, but also future scientific challenges. Older systems continue to be used for testing and training purposes.
• Interferometry: the precise measurement of the positions of radio sources. This includes astrometry, very long baseline interferometry (VLBI), connected element interferometry, interferometry arrays and orbiting interferometry as well as measurements of the station positions and the orientation of the earth for earth exploration.
• Radio science: Findings about the solar system and general relativity through experiments with radio waves between spaceships and the DSN. This could z. B. atmosphere, ionosphere, planetary surfaces, planetary rings, the solar corona, interplanetary plasma and the mass of planets, moons and asteroids can be determined.
• Radio and radar astronomy: Determination of information through signals that emanate or are reflected from natural celestial objects.
• Earth position: Determination of the locations of the radio stations and the earth orientation (geodesy).
• Sky observation: Identification and recording of radio sources to create a reference frame. This includes radiometry, polarimetry, spectroscopy and advanced spectral analysis. The DSN maintains a sub-network of 11-meter antennas that are used to support two very long baseline interferometry satellites. Both satellites should help to create high-resolution maps of natural radio sources and to use the possibilities of VLBI.

See also

• List of space probes
• ESTRACK

literature

• Jim Taylor: Deep Space Communications. Wiley, 2016, ISBN 978-1-119-16902-4 .

Web links

Commons : Deep Space Network  - collection of pictures, videos and audio files

• raumfahrer.net: - New antennas for Mars Express & Co.
• NASA: Deep Space Network Homepage (English)
• Deep Space Network Now constantly updated technical information about the communication between the DSN and various missions.

Individual evidence

1. ↑ History of Deep Space Station 51 at Hartbeesthoek. Hartebeesthoek Radio Astronomy Observatory, October 16, 2010, accessed September 3, 2012 . 
2. ↑ Mudgway, Douglas J .: Uplink-Downlink: A History of the Deep Space Network, 1957–1997 (NASA SP-2001-4227) (PDF file; English; 172 kB), page 5
3. ↑ History of Deep Space Station 51 at Hartbeesthoek. Retrieved October 14, 2017 . 
4. ↑ Megan Wallace: Follow the Sun. December 20, 2017. Retrieved April 27, 2019 . 
5. ^ Esa: ESA and NASA extend ties with major new cross-support agreement . In: European Space Agency . ( esa.int [accessed October 14, 2017]).
6. ^ Thuy Mai: Deep Space Network Aperture Enhancement Project. May 1, 2015, accessed March 10, 2019 . 
7. ↑ Antenna arraying - Deep Space Network. Retrieved March 10, 2019 . 
8. ↑ Jet Propulsion Laboratory (Ed.): Deep Space Network, 70-m Subnet Telecommunications Interfaces . Rev. G edition. No. 810-005 101 , September 4, 2019 ( nasa.gov [PDF]).