ESTRACK (ESA's Tracking Stations Network)
ESA's ESTRACK supports the Agency's and 3rd party spacecraft, during both critical and routine mission phases. In order to ensure the required continuous and reliable communication capability, a set of ground stations are placed at the Australian, American and European longitudes. In addition, an ESA terminal is hosted at Malindi, Kenya. As from 1968 this ground stations network has been augmented as mandated by mission requirements, whilst maintaining a general-purpose character to the maximum extent possible. The latter ensures integrity of the network, common interfaces to control centers, efficient spare holding capabilities, and thus its cost efficient operations and maintenance.
After having developed and operated a European network supporting low and near Earth spacecraft (e.g. Kiruna, Redu, Kourou), in the last years ESA focus has been put on the sustaining and development of a LEOP infrastructure (Kourou, Malindi and New-Norcia) and deep-space infrastructure (located in Australia, Spain and Argentina). At the same time, ESA has developed a partnership with cooperative agreements and commercial suppliers complementing the ESA capabilities for the support of critical and routine operations in the Earth-Earth domain. This paper focuses on the strategic evolution of ESTRACK, ensuring that such strategic asset for Europe will be able to support the ESA future missions roadmap. 1)
Some background: In the sixties, during the early phase of the space exploration era, Europe initiated its space venture, including launchers and ground infrastructure programs. In the early seventies, the European Space Agency started to deploy its 15 meter antennas around the world with ground stations in Redu (Belgium), Villafranca (Spain), Odenwald (Germany), Kiruna (Sweden), Kourou (French Guyana). In the eighties, Carnarvon (Australia) complemented this set of ground-stations for the support of the first ESA deep space mission: Giotto. The Carnarvon antenna was moved in 1986 to Perth.
In the nineties and with the development of a deep-space program led by Rosetta, ESA decided to initiate the procurement of a first deep-space antenna to be located in New-Norcia (Australia). The inauguration of that antenna took place on the 5th of March 2003. Two antennas in Cebreros in 2005 (Spain) and Malargüe in 2013 (Argentina) complemented the ESA deep-space network.
In 2008, ESA deployed a 5.5 meter antenna on Santa Maria Island in the Azores archipelago, Portugal, in order to track Ariane launchers. The initial purpose was the launch of ATV (Automated Transfer Vehicle) missions for the ISS on board Ariane 5. That antenna is still in use for the tracking of Arianespace launchers.
Finally, in the 2010 decade, ESA deployed two small antennas, one in New-Norcia (Australia) for LEOP and launcher tracking support and one in Malindi (Kenya) for LEOP support.
In parallel to the extension of ESTRACK, ESA established a cooperative network (Figure 1, green sites) with other Agencies (e.g. NASA, JAXA, CNES, DLR, etc.).
As ESA celebrates the 100th launch of Ariane 5 in September 2018, the Agency's worldwide ground station network is also marking ten years of providing vital tracking services to launchers soaring out of Kourou. 2) 3)
ESA's Earth-orbiting satellites and probes out in the Solar System are ultimately dependent on a small network of ground antennas, keeping them connected to their home planet. For ten years, this network has also been doing the same job for Europe's high-flying launchers.
Figure 1: ESA Tracking Stations Network (ESTRACK). The map is showing locations of Estrack stations as of 2017 (image credit: ESA)
Legend to Figure 1: This map is representational only and not all locations are shown with complete accuracy. The ESA tracking station at Perth, Australia, was retired from service in December 2015. The ESA stations at Villafranca and Maspalomas, Spain, were transferred to industry in 2017.
•Blue indicates core ESA-owned stations operated by the Estrack NOC (Network Operations Center) located at ESA's European Space Operations Center (ESOC), Darmstadt, Germany. 4)
• Orange indicates Augmented Estrack stations, procured commercially and operated on behalf of ESA by commercial entities.
• Green indicates Cooperative Estrack stations owned and operated by external agencies, but regularly providing services to ESA missions on an exchange basis.
"ESA's ventures into space have sent back vast quantities of scientifically vital data and beautiful images from our Solar System, yet without this little-known network, most of these incredible insights would never have reached Earth." explains Gerhard Billig, responsible for managing launcher tracking support at ESA's operations center in Germany (ESOC).
Named ESTRACK, this global system of ground stations provides links between satellites in orbit and the teams on Earth that control them, and of course the scientists who analyze their data.
The core Estrack network comprises seven stations in seven countries on three continents, all are centrally controlled from the Agency's operations center in Darmstadt, Germany. Four of these stations are used for tracking satellite or launchers near Earth and feature 13 m, 13.5 m or 15 m dish antennas: Kourou (French Guiana), Redu (Belgium), Santa Maria (Portugal) and Kiruna (Sweden).
ESA's ground network was established in 1975, with the first 15 m-diameter station located at Villafranca del Castillo, Spain, for the International Ultraviolet Explorer mission (and since then, the original Villafranca location has expanded to become ESAC (European Space Astronomy Center), ESA's major establishment in Spain.
In a typical year, the Estrack network provides over 15,000 hours of tracking support to 20 or more missions, with an enviable service availability rate above 99%.
Figure 2: Aerial view of the Redu station (image credit: ESA)
The activities at the ESA Redu core station include one antenna, RED-1, currently used for providing TT&C support to the Galileo program. This support is formally confirmed until end 2018, further extensions might be possible. The loading of the RED-1 core station is therefore satisfactory until the end of the support to Galileo program.
New Strategy: With the increased number of supported missions as well as the development of commercial facilities, ESA decided to re-center its ground segment approach around three axes:
1) Maintain and develop strategic owned components for deep-space, astronomical and EO missions as well critical support such as LEOP, maneuver, launcher tracking...
2) Maintain and develop cooperation with other agencies, building partnership and cross-support with both non European and national European agencies.
3) Develop a commercial partnership for routine support of near-earth missions. In this context, ESA has handed over to national entities assets that were not any longer considered mandatory and somehow redundant with commercial capabilities. The following sites were affected:
- The Perth antenna was dismantled and handed-over to Portugal in 2017. The 15 meters antenna will be used in Santa-Maria for commercial purposes.
- The Villafranca and Maspalomas antennas were handed over to Spain in 2017.
ESA Low and Near Earth Missions Infrastructure: Located in the northern part of Sweden, the Kiruna site is made available to ESA based on an international agreement between ESA and the government of Sweden (1986).
The station is equipped with two terminals, namely Kiruna-1 (KIR-1) and Kiruna-2 (KIR-2) are Cassegrain antennas, both providing S-Band transmit and S- and X-band receive capabilities (S/SX). The Kiruna-1 antenna is a 15m parabolic main reflector and a shaped hyperbolic subreflector in an elevation over azimuth over tilt axis mount.
The Kiruna-2 antenna is a 13m parabolic main reflector and a dichroic hyperbolic subreflector with heater (S-band pass through, X-band reflection), in an elevation over azimuth over tilt-axis mount.
The two terminals provide the following services:
• TT&C and payload data reception
• Radiometric measurements (Ranging, Doppler, Meteo, Autotrack Angles)
After the first frequency down-conversion stage, the downlink L-band signals of KIR-1 and KIR-2 are fed via the Antenna Downlink Switch (ADLS) into tunable L-band down-converters for conversion to 70 MHz intermediate frequency (IF) and further signal routing through the 70 MHz switch.
Telecommands are received at the station using the SLE protocol and transmitted to the frequency upconverters at 230 MHz. The uplink signal is routed to the KIR-1 and KIR-2 S-band uplinks or alternatively to the ESRANGE terminals.
Figure 3: Aerial view of the Kiruna station (image credit: ESA)
In addition to the Kiruna infrastructure, the Kourou Diane core station (KRU) is currently primarily allocated to the support of XMM-Newton. The loading of the Diane station is therefore satisfactory at least until the end of the XMM mission. The station is ideally located for LEOP support to Near Earth missions also with highly elliptical orbits and features a dedicated X-Band Acquisition Aid. As such it will be supporting the execution of the critical LEOP of upcoming missions, namely Galileo, Metop-C, BepiColombo, and SOLO (Solar Orbiter). The Kourou station is considered a strategic infrastructure enabling ESA to execute autonomously the critical operations of its missions. In fact the Sand X-band LEOP capabilities in Kourou are not easily replaceable by commercial services or international support. In the mid term, considering its characteristics, it is expected that the Diane station will also be ideally placed to support the future (cis)-lunar exploration missions.
The terminal is a Cassegrain antenna with a reflector system, parabolic main reflector and hyperbolic sub reflector, with shaped contours for high gain and low side lobes. The antenna has S/X-band transmit and S/X-band reception capabilities (SX/SX). The back-end Telemetry and Telecommand interface is based on SLE services.
Figure 4: Aerial view of the Kourou Diane core station (KRU), image credit: ESA
Low and Near Earth Missions Needs: Currently Earth Observation (EO) missions are typically operated in S-band (TT&C) with payload data transmitted in X-band (8.025-8.4 GHz). Polar orbit of most of the EO spacecraft dictates the location of the ground stations at polar regions, which increases interference and congestion in X-band due to limited available bandwidth. Interference and congestion will not be limited to X-band but due to terrestrial communication needs it will also likely affect S-band.
To overcome the congestion issue and to provide higher data rates the 26 GHz frequency band has been allocated (25.5-27.0 GHz, K-band) to dump payload data. Missions like NASA/NOAA Joint Polar Satellite System (JPSS-1) recently launched and EUMETSAT EPS-SG (EUMETSAT Polar System Second Generation), planned to be launched starting in 2021, will transmit payload data at 26 GHz. TT&C will still be in S-band.
Both JPSS-1 and EPS-SG will be operated by dedicated antennas in S-band for TT&C and will receive payload data by dedicated antennas operating at 26 GHz. In order to establish a reliable link with the satellite an antenna of a minimum size of 6m will be required at 26 GHz.
The new Sentinel missions (i.e. Sentinel expansion/extension) currently under initial preparation might also consider transmission of payload data at 26 GHz.
In summary, future EO missions might adopt novel approaches, moving from the current configuration (TT&C in S-band, payload data in X-band) to novel solutions [TT&C services in X-band and payload data at 26 GHz (K-band)].
This evolution in the EO space segment requires an equivalent adaptation of the ground segment, in particular as regards the ground stations capabilities.
ESA Low and Near Earth Strategy: As presented previously, future EO missions will likely adopt novel approaches, moving from the current configuration (TT&C in S-band, payload data in X-band) to novel solutions (TT&C services in X-band and payload data at 26 GHz (K-band)). In the past years a series of ground segment technology activities have been conducted in order to anticipate the above evolution and enable the provision of communication services.
Based on this, a feasibility study shall be conducted to assess the possibility to upgrade the existing KIR-1 terminal by adding X-band uplink (as required for future EO missions) as well as autotrack capabilities in this frequency band. In addition, the option to add K-band reception capabilities shall be evaluated.
Based on this, a feasibility study shall be conducted to assess the possibility to upgrade the existing KIR-1 terminal by adding X-band uplink (as required for future EO missions) as well as autotrack capabilities in this frequency band. In addition, the option to add K-band reception capabilities shall be evaluated.
In 2018, ESA will acquire a new 6m S/K-band antenna as part of a dedicated project. As a follow-on initiative, it is envisaged to deploy this terminal at the Kiruna station, providing enhanced capabilities in support of current and future EO missions. Initially it could be used as test and validation facility in support to JPSS-1 and EPS-SG. Later it will be able to provide services to ESA and other partners EO missions (e.g. new Sentinels and Earth Explorer missions). A detailed plan covering the conversion of the prototype into a full operational system is being prepared.
By 2020 the following capabilities will then become available in ESA Kiruna Station:
1) KIR-1: 15 m antenna operating in S/X-band but designed to be easily upgraded to X-band uplink for upcoming EO mission requiring TT&C services in X-band
2) KIR-2: 13m antenna operating in S/X-band (unchanged)
3) KIR-3: 6m antenna for K-band payload data reception.
Deep-Space and Astronomy Mission Needs: An estimate of the ground stations utilization has been performed covering the next decade, and taking into account the ESA missions under development as well as potential missions such as L5 Space Weather (ESA) and WFIRST (NASA). Official launch dates and nominal mission lifetime have been retained . Among the future missions, of particular relevance is ESA Space Weather spacecraft, with a launch assumed in 2023. With its 24/7 operational profile, this mission will require high performance deep space communication services.
Furthermore, the analysis assumes launch of NASA WFIRST mission in 2025. ESTRACK will provide communication services during the complete duration of this mission.
Based on the above analysis, the estimated load of ESA's three deep space antennas over the time frame 2018-2030 indicates a major increase as of 2021. By 2023 the communication needs of the missions will exceed by up to 50% the currently available capacity.
The implementation of additional resources is deemed necessary: up to two new 35 m antennas deployed over Australia and Argentina longitudes respectively, are essential in order to support the average 26,000 tracking hours/year required by the upcoming missions.
In summary, independent access to space remains a strategic objective for Europe. While in the future, space missions will be more and more demanding in terms of performances (e.g. increased data throughput) and capabilities (e.g. new frequency bands), the needs for optimizing the costs and possibly sharing the facilities is an important aspect of ESA's future activities.
To that end ESA considers necessary to develop partnership approaches either in a cooperation model, or possibly in a co-owning model ensuring an optimization of the use and of the associated running costs. ESA is today embarking in such strategic development and has initiated discussions with partner agencies. The future of space activities in space or in ground will require increased cooperation and increased partnership.
The development of new technology whether for near Earth, LEOP or space exploration remains as well a strategic targets. To that end a number of studies aim at preparing European technology for the future requirements targeting at improving performances and capabilities of the network.
On medium term, ESA intends to extend the existing deep-space sites by deploying additional deep-space terminals in New-Norcia (Australia) and in Malargüe (Argentina) as well as maintaining and developing strategic assets such as Kiruna (Sweden) and Kourou (French Guyana).
Figure 5: ESTRACK - ESA tracking station network profile (video credit: ESA)
Status of ESTRACK
• January 2019: Planned installation of cryogenically cooled antenna feed. 5) This year, ESA's ground station boffins are planning to deploy a new cryogenically cooled "antenna feed" – a gizmo used to transmit and receive deep space signals – on the Agency's three deep-space antennas.
- The ground stations routinely communicate with missions like BepiColombo – heading to Mercury, Gaia – surveying stars in our Galaxy, and ESA's two spacecraft at the Red Planet, Mars Express and the ExoMars Trace Gas Orbiter.
- ESA's 35 m antennas receive data from working spacecraft, in what's called a ‘downlink'. As the Agency prepares to launch new missions deeper into our Solar System in the next few years, including Juice to Jupiter and the ExoMars Rover, as well as missions designed to generate large quantities of data, such as the future Sun-watching Lagrange mission, use of the stations' downlink capacity is set to grow significantly.
- This means the stations have to 'up their game', and the new antenna feed is expected improve data return by 40% at the high frequencies used for spacecraft command and control. The feed must be cooled to just 10 K (just 10 degrees from absolute zero, about -263 C) for normal operation.
- "While receiving extremely faint signals, the new feed should be capable of transmitting command signals to spacecraft at very high power of more than 25 kilowatts", says ESA ground station engineer Stéphane Halté. "This is similar to the amount of power transmitted by 25,000 mobile phones switched on simultaneously."
- The prototype antenna feed was mounted on NASA's Deep Space Station 13 (Figure 6), at NASA's High Power Transmitter Test facility, in Goldstone, California. It was tested in December 2018 with the assistance of experts from the NASA Jet Propulsion Lab's Deep Space Network.
- Testing successful, this ESA/NASA cooperation has cleared the way for the new technology to be rolled out at across ESA's deep space ground stations, part of the Estrack network, within this year.
Figure 6: NASA's Deep Space Station 13, at NASA's High Power Transmitter Test facility, in Goldstone, California (image credit: ESA, S. Halté)
• Ten years of launcher tracking - 2018 (Ref. 4): In addition to catching signals from satellites almost anywhere, 2018 marks ten years since Estrack stations began tracking the launch vehicles that deliver these satellites into orbit, starting in March 2008, with the Ariane 5 rocket that carried the ATV-1 cargo vessel, Jules Verne.
Initially established to communicate solely with satellites, Estrack was expanded to support their rockets in 2008 with the establishment of a ground station and 5.5 m-diameter antenna on Santa Maria Island in the Azores archipelago, Portugal. The first Estrack station with the capability to track launchers, Santa Maria provided ESA with the independent means of receiving information from launchers through all phases of their flights.
Santa Maria joined Estrack at the same time that the Automated Transfer Vehicle (ATV)-series of missions got underway; the five ATVs were a series of expendable spacecraft developed by ESA to carry supplies to the International Space Station, at about 400 km altitude.
The special Ariane launch trajectory for these missions required a dedicated station in the middle of the Atlantic Ocean. For the same reason, this station has continued to be used for all launches of Galileo satellites, helping orbit Europe's new navigation system.
In contrast, the original Ariane launcher tracking station network — operated by the French space agency CNES from Europe's Spaceport in Kourou — is tailored for a different launcher trajectory followed by most launches from Kourou. These deliver telecom satellites into geostationary orbit at 36,000 km.
Santa Maria tracks all launch vehicles operated from Europe's Spaceport: including the three world-changing launch vehicles, Ariane 5, Soyuz and Vega.
Estrack stations provide teams on site with vital information acquired from the launchers soaring overhead, which is then passed on to the CNES and Arianespace teams who control their flights.
"ATV-2 in 2011 was a particularly memorable launch," says Gerhard, who was at Santa Maria station at the time. Just minutes after liftoff from Kourou, while the Ariane rocket was in radio contact with our station, we could see it whizzing high over our heads in the clear night-time sky. We could actually make out the upper stage thruster burning! It was amazing to see the rocket speed across the horizon, like a comet through the sky. And what we saw visually, was being confirmed on our screens via the live telemetry link."
To date, the Estrack stations in Portugal and Western Australia have supported 35 launches, many of which were monitored by more than one ground station; 16 launches have been supported from Santa Maria, and 34 from Western Australia (20 from Perth and 14 from New Norcia).
Figure 7: ESA's Santa Maria ground station is located on the ‘Montes das Flores' (Hill of Flowers) on Santa Maria island in Portugal's mid-Atlantic Azores. It includes a Galileo Sensor Station (image credit: ESA)
Upgrading down under: In 2010, the existing New Norcia antenna in Perth, Western Australia, was upgraded for launcher tracking. It was used for tracking not only ATV and Galileo launches but also rockets delivering satellites to ‘Sun-synchronous orbits' and onto interplanetary trajectories.
"For a decade now, tracking services for both the launcher and the satellite are provided, a unique and important capability during the first, critical moments of a satellite's mission," says Gerhard.
In 2010, the existing New Norcia antenna in Perth, Western Australia, was upgraded for launcher tracking. It was used for tracking not only ATV and Galileo launches but also rockets delivering satellites to ‘Sun-synchronous orbits' and onto interplanetary trajectories.
"For a decade now, tracking services for both the launcher and the satellite are provided, a unique and important capability during the first, critical moments of a satellite's mission," says Gerhard.
Since the closure of the Perth station in 2016, its launcher tracking capability has been transferred to ESA's deep space station at New Norcia, also in Western Australia.
• Transferring ownership of three ESA ground stations: 6)
As part of ESA's strategy to foster commercial competitiveness in Europe while focusing on its core aims, the agency has transferred ownership of several ground tracking stations for reuse by external organizations. By the end of 2017, ESA will have transferred three stations to national organizations in Spain and Portugal, who will take over the provision of satellite tracking services to a wide variety of commercial customers.
The three stations involved in the transfer are all equipped with 15 m-diameter dish antennas, suitable for supporting near-Earth missions, and are located in Spain, at Maspalomas and at ESA's space astronomy center near Madrid, and in Perth, Western Australia.
The new operators will be able to use the stations to offer tracking services on a commercial basis to customers worldwide, which also includes ESA, leaving the Agency free to focus on meeting the demanding technical requirements of its deep-space stations, in Spain, Argentina and Australia, and on operation of a select group of four other stations.
"The handover increases commercial capabilities and capacity in Europe, not only to the benefit of ESA but also for commercial partners," says Yves Doat, Head of Ground Facilities Infrastructure at ESA's mission control center, Darmstadt, Germany. "ESA will continue developing the new technologies needed for future communication, including very high data-rate optical communication and networking with exploration partners at the Moon, Mars and other deep-space destinations."
The handover of the Perth station was notable. The station's frequency licence was withdrawn by the national telecoms regulator in 2015, and the station could no longer operate where it was. After being decommissioned, ESA was faced with the not insignificant cost of tearing it down and disposing of the structure and technical equipment.
"Instead, the government of Portugal made a bid for the station and, following a cost-sharing agreement for dismantling and transportation, it was shipped to Santa Maria island, in the Azores, where it is being recommissioned and placed back into service by 2018," says Yves.
Augmented network: The ESA-owned and operated core Estrack network is complemented by commercially operated stations provided thru service contracts with organizations such as the Swedish Space Corporation (SSC), Spain's National Institute of Aerospace Technology (INTA) and Kongsberg Satellite Services AS (KSAT, Norway).
These include tracking stations located at South Point, Hawaii (USA), Santiago (Chile), TrollSat, Antarctica, and Svalbard (Norway) and Dongara (Australia). These stations are used especially during the LEOP phase of a mission immediately following launch, when the flight control team needs continuous communication with their satellite, beyond what can be provided by ESA's own stations.
International cooperation: ESA shares Estrack capacity with other space agencies, who in return provide tracking services to ESA missions under a number of resourcing-sharing agreements. These include networks and stations operated by ASI (Italy), CNES (France), DLR (Germany), NASA's Deep Space Network and Goddard Space Flight Center and JAXA (Japan).
For example, NASA's Deep Space Network stations routinely support Rosetta and Mars Express (as well as other, now-complete missions such as Huygens and Venus Express), while Estrack is supporting Japan's Hayabusa-2 mission to asteroid 1999 JU3 (arriving in 2018). In recent years, Estrack has provided support to missions operated by China and Russia, as well as tracking the descent of NASA rovers to the surface of Mars.
This global cooperation allows all agencies to make use of a wide number of ground stations in geographically advantageous locations, maximizing efficiency and enhancing scientific returns for all. This cooperation is made possible, in part, through ESA's strong support for the development and adoption of internationally recognized technical standards for sharing tracking data.
In accordance with ITU radio regulations and agreements between ESA and Estrack host countries, Estrack stations are fully licensed and their operation respects requirements such as minimum elevation angle and maximum power radiated, as well as any site-specific constraints included in these agreements.
Estrack stations are designed in accordance with the European Cooperation for Space Standardization (ECSS) standards.
DSA (Deep Space Antennas)
In 1998, ESA decided to establish its own network for tracking deep-space probes to cope with the expected rapid rise in the number of interplanetary missions. The aim was to establish three terrestrial stations about 120° apart in longitude to provide continuous coverage as Earth rotated.
In the 2000s, the first of three 35 m-diameter Deep Space Antennas (DSA) was built in New Norcia (Australia), followed by stations at Cebreros (Spain) and Malargüe (Argentina). These feature some of the world's best tracking station technology and enable communications with spacecraft voyaging hundreds of millions of kilometers in space. In August 2016, New Norcia station received signals from the international Cassini spacecraft orbiting Saturn, across more than 1.4 billion km of space.
ESA Deep-Space Station Infrastructure: The deep space tracking network, part of the ESTRACK core network, consists on a set of three 35m class ground stations, distributed around the world and located in: Cebreros (Spain), Malargüe (Argentina) and New-Norcia (Australia). The ESTRACK deep-space network is suitable for a wide range of missions: interplanetary, space astronomy, solar observation, lunar exploration, etc. Since its debut, it has supported all major ESA scientific missions, including Rosetta, Mars Express, Venus Express, ExoMars, and Gaia. The network is also used in cross-support of other's agencies mission such as: Cassini (NASA), Insight (NASA), Hayabusa (JAXA).
The three terminals provides the following services:
• Radiometric measurements (Ranging, Doppler, Meteo, ΔDOR)
New Norcia Facility: DSA-1:
In March 2003, ESA inaugurated a new deep-space station 8 km south of the town of New Norcia, which is about 150 km north of Perth, in Western Australia. — The large antenna was completed in 2002, and engineers conducted pointing tests using NASA's Stardust mission in the lead up to operational readiness. It entered service as the first of the Agency's three deep-space tracking stations in March 2003, and has been used for communications with Mars Express, Rosetta, Venus Express and Gaia, among other ESA and partner agency missions. The antenna supports data transmissions and receptions in both S- and X-band.
The coordinates of the 35 m antenna are: -31° 2' 53.61", +116° 11' 29.40". The antenna is sited at 252.26 m with respect to the WGS-84 reference ellipsoid, a mathematically- defined reference surface that approximates the Earth's geoid surface.
Figure 8: ESA's New Norcia station, DSA-1 (Deep Space Antenna-1), hosts a 35 m-diameter parabolic antenna. DSA-1 communicates with deep-space missions, typically at ranges in excess of 2 million km. It is also capable of supporting the ultra-precise 'delta-DOR' (Delta-Differential One-Way Ranging) navigation technique (image credit: ESA/S. Marti) 7)
As of 2017, ESA's deep-space ground station at New Norcia, Western Australia, is also being powered in part by sunlight, thanks to a new solar power ‘farm' completed in August. The farm has 840 photovoltaic panels arranged in five double rows with a rated capacity of 250 kW. This is expected to generate 470 MWh of electricity annually, about 40% of the station's annual needs and equal to the electricity needed to power 134 typical households. 8)
"While we've only just completed the first full month of operation, the solar facility has already reduced our cost of purchasing electricity from the local power company by at least 30%," says ESA's Marc Roubert. "In the coming summer months, given some sunny, clear skies, we even expect to be able to deliver electricity back to the local grid."
The installation began in 2015 and is expected to provide a full return on investment within about 15 years. — In future, ESA will consider upgrading the sites in Spain and Argentina with solar power as well.
Status of DSA-1
• December 20, 2018: ESA's 35 m antenna in Australia has now been powered by the Sun for over a year, cutting costs and reducing carbon emissions by 330 tons - equivalent to 1.9 million km driven by car. 9)
- The solar plant at the New Norcia station in Western Australia started its first full month catching solar rays in August 2017. One year later, it had produced 470 Megawatt-hours of power – enough to supply 120 four-person homes for a year, fuelling 34% of the total electricity consumption of the station
- In order for the tracking station to be powered 100% by renewable energy, more panels would be required. Other sources of energy could also be used such as kite power, hydrogen or geothermal energy.
- "I am really happy with these results – they reach beyond our initial expectations when we began the solar-power upgrade and I would be thrilled to see the same development spread to our other ground stations," explains Marc Roubert, ESA's ground stations maintenance engineer.
- With this success, ESA engineers will investigate possible similar upgrades for other stations.
- Ultimately, Marc says, it would be a real achievement to get all ESA ground stations in the Estrack network completely off the mains power grid. This way, they can continue to track and communicate with satellites orbiting Earth and in deep space, while reducing the carbon footprint of the Agency's giant 'eyes on the skies'.
Figure 9: ESA's deep-space antenna in New Norcia, Western Australia, has now been powered by solar energy for over a year, in the first step towards creating a green network of eyes on the skies (image credit: ESA/D. O'Donnell, CC BY-SA 3.0 IGO)
• December 14, 2018: Australia's national science agency, CSIRO (Commonwealth Science and Industrial Research Organization), has been selected to provide maintenance and operational support for the European Space Agency's deep space tracking station at New Norcia, 130 km north-east of Perth in Western Australia. 10)
- This is the first time that an Australian organization has been selected to manage day-to-day operations at the ground station. The ESA control center in Darmstadt, Germany will continue to remotely control its spacecraft and satellites via the station.
- A 35 m antenna at the tracking station, DSA-1, provides support to ESA's missions exploring our solar system. It tracks their locations, sends commands to control spacecraft, and reliably receives data collected hundreds of millions of kilometers from Earth.
- These missions include BepiColombo, which was launched in October 2018 and will explore Mercury – the closest planet to our Sun – where it will endure temperatures in excess of 350°C; and Mars Express, which is currently orbiting the Red Planet collecting information about its geology, atmosphere, surface environment, history of water and potential for life. ESA's ExoMars trace gas orbiter and Gaia mission are also supported.
- The station provides tracking support to scientific and interplanetary missions operated by other international space agencies like NASA and Japan's JAXA under resource-sharing agreements.
- The station provides tracking support to scientific and interplanetary missions operated by other international space agencies like NASA and Japan's JAXA under resource-sharing agreements.
- The contract is due to start on 1 June 2019; a three-month handover from the current contractor will start on 1 March 2019.
- Federal Minister for Industry, Science and Technology Karen Andrews said the agreement was another important milestone in the growing Australian space sector. "Since 1979, Australia and ESA have had treaties in place to enable European Space Agency ground stations on Australian soil to track spacecraft and interplanetary missions and Australia has unique view of the southern hemisphere sky that provides us with a natural advantage for viewing the Universe," Minister Andrews said.
- "The facility at New Norcia has been in operation since 2003 and now, for the first time, an Australian organization will provide critical maintenance and operational support at the station. Through its management of NASA's Canberra Deep Space Communication Complex, as well as Australia's leading radio astronomy facilities, CSIRO has rich experience operating large, complex infrastructure for spacecraft tracking and astronomy research. - This follows the announcement earlier this week that Adelaide will be the location of the Australian Space Agency, and is a further demonstration that momentum is building for the local space industry. The space industry plays an essential role in the lives of all Australians, from providing us with weather forecasts and telecommunications, to inspiring the next generation of students."
• On 26 October 2018, a group of EU Ambassadors to Australia (including Australia, Belgium, Croatia, Cyprus, Czech Republic, France, Greece, Hungary, Italy, Netherlands, Slovenia) visited ESA's deep space ground station at New Norcia, Western Australia. 11)
Figure 10: EU ambassadors to Australia were recently shown around ESA's New Norcia tracking station. Peering up from the Western Australian desert, two antennas have captured some of the Agency's most beloved missions (image credit: ESA/ G. Billig)
- ESA's deep space stations feature some of the world's best tracking station technology and enable communications with spacecraft voyaging hundreds of millions of kilometers in space.
- The New Norcia station's geographic location on the western side of Australia enables it to not only communicate with missions traveling deep in our solar system, but also to track rockets launched from ESA's Spaceport in Kourou, French Guiana, acquiring the 'first signals' from newly orbited satellites.
- Gerhard Billig, responsible for managing launcher tracking support at ESA's ESOC operations center in Germany, showed the ambassadors around the station, briefing them on the critical support it has offered to some of ESA's best known missions, including Exomars, BepiColombo and Gaia.
- Ambassadors were also given a tour of the 35 m-diameter deep dish antenna — in August 2016, this station received signals from the international Cassini spacecraft orbiting Saturn, across more than 1.4 billion km of space, the most distant 'catch' ever made by ESA.
- The tour also included the ‘NNO-2' small dish and the technical facilities. The NNO-2 dish was established in 2015 and has since caught the signals from newly launched satellites, including the latest, Aeolus and BepiColombo.
Cebreros Facility: DSA-2:
ESA's new deep space radio antenna in Cebreros (Ávila, Spain) was officially inaugurated on 28 September 2005. The new 35 m antenna is ESA's second facility devoted to communications with spacecraft on interplanetary missions or placed in very distant orbits. Cebreros' first task was that of tracking ESA's Venus Express spacecraft. 12)
Figure 11: ESA's 35 m-diameter deep-space dish antenna, DSA-2, is located at Cebreros, near Avila, Spain. It is controlled, as part of the Estrack network, from ESOC (European Space Operations Center) in Darmstadt, Germany (image credit: ESA)
Malargüe Facility: DSA-3:
The Malargüe station, Deep Space Antenna 3, is ESA's newest tracking station and is located 30 km south of the city of Malargüe, about 1200 km west of Buenos Aires, Argentina. DSA 3 hosts a 35 m-diameter antenna with transmission and reception in X-band and reception in Ka-band. 13) 14)
DSA 3 was inaugurated in December 2012 and entered full service in early 2013. Today, it provides daily support to missions such as Gaia, Mars Express, Rosetta and ExoMars.
Figure 12: Malargüe station supports many of ESA's most important exploration missions, including Rosetta, Mars Express, ExoMars, LISA Pathfinder and Gaia. It will also support cornerstone ESA missions like ExoMars 2020, BepiColombo and Juice, as well as partner missions from Russia, the US and Japan, among others (image credit: ESA/D. Pazos - CC BY-SA IGO 3.0)
Location: The coordinates of the antenna are 35° 46' 33.63" S (35.776°S), 69° 23' 53.51" W (69.398°W), and the station is sited at 1550 m above sea level.
The Malargüe station incorporates state-of-the-art technology. Its technical facilities comprise Ka-band reception (31.8–32.3 GHz) and X-band transmission and reception. It is prepared to host Ka-band transmission (34.3–34.7 GHz) and K-band reception (25.5–27 GHz). Its main functions are to receive telemetry, send telecommands and perform radiometric measurements (ranging, Doppler, Delta-DOR) on scientific and deep-space craft.
Operations: The station provides routine spacecraft tracking support to ESA's deep-space missions such as Venus Express and Mars Express, and scientific missions such as Herschel and Planck, as well as to other agencies' missions under resource-sharing agreements. Malargüe will also support future ESA scientific missions, including LISA Pathfinder, Gaia and BepiColombo.
For routine operations, the station is remotely controlled from ESOC, Darmstadt, Germany. Local maintenance and operation is provided by a team of five engineers.
Status of DSA-3
April 11, 2019: ESA's 35 m radio antenna in Malargüe, Argentina, has had a major refurbishment. Extensive modifications made will now allow the ESTRACK network to support future mission like Euclid, launching in 2022, and to transfer data at much higher rates. 15)
Currently missions like Gaia are able to send back data at a channel rate of 10Mbit/s. Euclid will send back data at a rate of 149Mbit/s – a similar increase in speed as we have experienced in our internet browsing in the last 10 years.
Euclid, which will orbit at the Lagrange point L2, will be fitted with the 26 GHz band radio giving it a higher bandwidth for transferring data to and from Earth, significantly increasing the scientific information returned over time.
The refurbishment of Cebreros and Malargüe stations, will allow ESA deep space antennas to receive broadband signals at 26GHz as well as the conventional X-band frequency.
Highlights of the upgrade
The core of the Malargüe Ground Station antenna optical system is the beamwaveguide. This is a set of mirrors that redirect the signal from the spacecraft to the antenna feeding system.
The central mirror in the set plays a key role in the upgrade. By rotating the mirror in the center, you can redirect the signal to different receivers with different frequencies.
When the central mirror is rotated to the deep space position, operators will be able to simultaneously use X-band and Ka-band waves – the kind of signal sent by deep space missions like BepiColombo.
When the central mirror is rotated to the near earth position, a newly developed multiband feed system will enable simultaneous X-band and K-band communications.
There is a placeholder position for exclusive communication at X-band using the new 80 kW high power amplifier. The 80 kW amplifier is currently being developed and is expected to be deployed to ESTRACK by 2024.
In addition, a new generation of low-maintenance cryogenic amplifiers for improved performance have been installed, as has the latest portable satellite simulator – which will be compatible with Euclid's high data rates.
Figure 13: Photo of the Malargüe station (image credit: ESA / Filippo Concaro)
Challenges to upgrade
This upgrade has provided unique challenges for the teams charged with seeing it through. The mirrors must be very precisely aligned, with a maximum of 3.5 millidegrees of angular tolerance. To achieve this precision, photogrammetry was used.
ESTRACK antennas also support a very wide range of flying missions, with a high operational load. To minimize the impact on operations, the complete refurbishment had to be completed in only five weeks.
Teamwork is key
The success of the upgrade relied on the dedication and expertise of each individual and their capability to work together effectively as a team.
Coordination between more than twenty people carrying out the upgrades has been paramount – and it has been achieved by keeping the team motivation high and ensuring communication and information flowed among the five industrial partner companies who worked together on the refurbishment.
Goonhilly goes deep space
ESA has three deep-space dishes, in Australia, Spain and Argentina, that provide leading-edge performance and full-sky coverage for tracking and communicating with missions like Mars Express, Gaia and ExoMars. Later this year, they will add the new BepiColombo mission to Mercury and, in the near future, ESA's Solar Orbiter, Euclid and Cheops. 16)
"The amount of science data flowing in from ESA's current missions, not to mention from future missions with improved instruments, is growing strongly," says ESA's Pier Bargellini, responsible for network operations. "By the middle of the next decade, ESA's deep-space communication needs for supporting today's missions, like ExoMars, and upcoming spacecraft, like Juice, is expected to exceed our present capacity by around half.
Developing commercial capacity: This is why ESA engineering teams are excited by a new initiative aimed at redeveloping part of Goonhilly Earth Station, an existing commercial station in Cornwall, UK, to enable it to provide Europe's first deep-space tracking services on a commercial basis.
Under the project, a 32 m-diameter dish built in 1985 will be upgraded to provide fast data links for missions far beyond Earth – typically exceeding 2 million km. In the future, once commercial capacity is available, ESA's deep-space antenna network will focus on supporting sophisticated missions demanding high-performance systems.
The project will be initially funded through a €9.5 million investment from the UK's Cornwall & Isles of Scilly Local Enterprise Partnership, a public–private regional economic development body, and will later include a smaller investment from ESA.
"Once the station upgrade work is complete, in about 24 months, Goonhilly will be able to complement ESA's own stations, and provide deep-space tracking for the Agency's missions as well as those of other space agencies or from private space start-ups aiming to exploit the Moon or mine asteroids," notes Klaus-Jürgen Schulz, responsible of ESA ground station engineering.
Goonhilly, established in 1962 and at one time the largest satellite station in the world, with over 60 dishes of varying size, is well known in the UK. Its antennas have brought iconic images to UK TV viewers, including Muhammad Ali fights, the Olympic Games, the Apollo 11 Moon landing and 1985's Live Aid concert.
With the growing demand for deep-space tracking for both space agencies and new commercial space companies, the Goonhilly upgrade is an excellent example of how ESA can foster new business for European industry through engineering contracts to transform existing antennas into state-of-the art deep-space ground stations.
Figure 14: Goonhilly Earth Station, a commercial tracking station in Cornwall, UK, will be upgraded to provide Europe's first deep-space services on a commercial basis (image credit: GES - Goonhilly Earth Station Ltd.)
Status of the station
• February 27, 2019: Satellite communications innovator and space gateway Goonhilly Earth Station has announced that it has inked a partnership agreement with the Australian Space Agency to collaborate and create new opportunities in the space economy in Australia, the UK and beyond. 17)
- The new statement of strategic intent and cooperation aims to help progress the Australian space sector and make the benefits of space more accessible for businesses, governments and institutions.
- One activity forming part of the agreement and already underway is Goonhilly's involvement in the proposed SmartSat CRC (co-operative research center) space research initiative. This consortium aims to enhance connectivity, navigation and monitoring capability across Australia and to maximize the country's resources by solving major satellite system and advanced communications challenges.
- Another is Goonhilly's commitment to help develop Australian-based deep space communication assets. Goonhilly opened an office in Australia in 2018, run by industry veteran Bob Gough, and will invest further in infrastructure and facilities as part of its wider plan to support deep space projects globally.
- The partnership will also help to make the benefits of space more accessible for Australian businesses. For example, Goonhilly's Enterprise Zone status is unique in the space industry, offering businesses from Australia and beyond the chance to be part of a rich space ecosystem and to build a cost-effective European base from which to grow their business.
- To help accelerate the growth of the Australian space economy, Goonhilly is also adopting its tried and tested UK business model, which is built around the development of close working relationships with local and national government, academia, business and other industry players.
- Dr Megan Clark AC, Head of the Australian Space Agency said: "We welcome Goonhilly's intent to invest in communications, and research and development in Australia. The agreement will provide greater opportunities for technology transfer and the creation of local skilled jobs in the space sector."
- "Both Goonhilly and the Australian Space Agency have a shared commitment to increase the opportunities afforded by space exploration and development. Through this partnership we will enhance the capabilities and competitiveness of both Australian and UK industry, to forge productive international collaborations and promote investments in space," commented Ian Jones, CEO of Goonhilly.
- The two organizations share a common vision: to forge international collaborations and promote investments in space capabilities and capacities that help to accelerate the growth of the Australian space economy; to help improve the lives of all Australians through the development of innovative products and services; and to provide new opportunities by enhancing the capability and competitiveness of Australian industry.
• January 29, 2019: Goonhilly Earth Station has announced that data center industry veteran Chris Roberts has joined the company's executive team as Head of Data Center and Cloud. 18)
- Chris's appointment comes as Goonhilly prepares to open a tier 3/4 data center in Spring 2019, offering exceptional connectivity by linking global subsea cables with satellite communications and fiber.
- Chris brings more than two decades' experience in the data center and cloud hosting industry including senior roles at Pulsant, Datapipe and iomart. His expertise in building high-growth cloud hosting and data center businesses via a mix of direct and indirect channels will be invaluable in his new role.
- Goonhilly's new high-specification data center's use of renewables, its Enterprise Zone status and its low latency connections are designed to make it a cost-effective choice for hosting and co-location customers in the satellite and broadcast industries as well as a wide range of enterprises. A national infrastructure asset for many decades, the Goonhilly site offers customers a high level of resilience, enhanced by its rural location and a secure energy source including green power from its onsite solar farm and local wind generation.
• January 7, 2019: Satellite Applications Catapult, UK, and Infostellar of Tokyo, Japan, have signed a memorandum of understanding (MoU) to provide UK businesses with enhanced access to the Satellite Applications Catapult's ground station in Goonhilly, Cornwall. 19)
- The Catapult's ground station is the primary ground location for its In Orbit Demonstration (IOD) program, a unique service that supports UK business to achieve the launch of satellite data services. By integrating this ground station with Infostellar's StellarStation service, organizations will be able to remotely access the Goonhilly station for uplink and downlink. The Catapult will also be able to share unused capacity with the StellarStation network to give greater access to their Goonhilly facility for UK companies.
- As a result of this collaboration, Infostellar plans to open a UK office at the Satellite Applications Catapult's Harwell base in 2019. The UK office will focus on business development and regulatory affairs for Infostellar's international expansion plans in Europe.
- With this agreement, the Satellite Applications Catapult continues to support innovative solutions for the small satellite community, as well as continuing to foster strong links between space companies in the UK and Japan.
Figure 15: Photo of the Goonhilly Earth station complex located on the Lizard Peninsula of Cornwall (image credit: Satellite Applications Catapult)
• November 23, 2018: Satellite communications innovator and space gateway Goonhilly Earth Station has joined the consortium backing the SmartSat CRC (Cooperative Research Center), a proposed space research initiative which plans to drive the Australian space industry through satellite technologies and analytics. 20)
- Led by the University of South Australia (UniSA), Airbus Defence and Space and Australian defence sector engineering specialist Nova Systems, in partnership with the South Australian Space Industry Center, the proposed plan for the establishment of the SmartSat CRC was developed starting early in 2018 and has been submitted to the Australian government for ratification.
- The first stage of the application process with the Federal Government has been successfully completed and the consortium is now preparing the final stage application, and working on next steps outlining the organization's parameters and discussing funding.
- The SmartSat CRC consortium aims to enhance connectivity, navigation and monitoring capability for the benefit of Australia, helping to maximize its resources by solving major satellite system and advanced communications challenges. The goal is to catapult Australia's space industry into a leadership position in several areas including intelligent satellite systems, advanced communications, and earth observation driven data analytics.
- The research consortium aims to co-develop intellectual property and specialist industry expertise that will spawn new businesses, create economic value and generate new high-tech jobs in Australia. Other economic benefits include applying advanced space technologies and space related data to diverse areas of society and the economy, from agriculture and the environment to healthcare and disaster detection and management.
- The 67-member SmartSat CRC consortium also includes blue-chip industry leaders Harris Corporation, Thales Australia, BAE Systems, Dassault Systems and other space engineering companies as well as partnerships with NASA, JAXA and UK Catapult and University College London (UCL).
- Professor Andy Koronios, Dean of Industry and Enterprise at UniSA, said: "With its technological and commercial expertise, as well as its expanding capabilities and resources, we are confident that Goonhilly will make a significant contribution to the SmartSat CRC."
- Dr Bob Gough, Head of Business Development, Australia and Asia-Pacific at Goonhilly, commented, "The space industry is a global one and Goonhilly is well poised to support Australian organizations as they look to extend their reach. At our UK site we offer world-class satellite capacity with visibility spanning 145 degrees West to 135 degrees East. enabling our customers to reach millions of people and receive sites in a single satellite hop. This is complemented by our connectivity with bundles of subsea cables and fiber, and our new multi-million-dollar datacenter."
- "Establishing a technical and operational presence in Australia is essential for Goonhilly as we fulfil our goal to create a worldwide deep space network; joining the SmartSat CRC perfectly complements this objective. We are bringing our business model of cooperation and collaboration which has been so successful in the UK, and we will use this proven approach in our numerous SmartSat CRC projects."
- "With the global industry leaders and world-class university researchers in SmartSat CRC, there is huge potential to develop new space industry opportunities that benefit all of Australia and the broader Asia Pacific," Gough added.
- SmartSat CRC is determined to accelerate the nation's space industry momentum following the July 1st establishment of the Australian Space Agency, which was the launchpad for developing space-based opportunities to enhance businesses and communities.
• April 17, 2018: ESA has signed a collaboration agreement with Surrey Satellite Technology Ltd (SSTL) and Goonhilly Earth Station (GES) for Commercial Lunar Mission Support Services at the Space Symposium in Colorado Springs, USA. This innovative commercial partnership for exploration aims to develop a European lunar telecommunications and navigation infrastructure, including the delivery of payloads and nanosats to lunar orbit. 21)
- The partnership allows for a low-risk, phased approach to implementing a sustainable, long-term commercial service and will support lunar scientific and economic development across Europe and the rest of the world. The agreement includes the upgrade of the Goonhilly Earth Station for commercial deep space services and the development of the space segment with a lunar pathfinder mission. The cooperation also encompasses the commercial and regulatory support to catalyze the lunar economy and provide affordable access to the lunar environment, and ultimately deep space.
- The agreement was signed by Sir Martin Sweeting, founder and Executive Chairman of SSTL, Ian Jones, founder and Chief Executive of GES and David Parker, Director of Human and Robotic Exploration at ESA.
- David Parker commented, "The agreement between ESA and SSTL/GES establishes ESA's first partnership for providing commercial services in support of lunar missions. The Lunar Pathfinder mission would provide exciting new opportunities for science and technology demonstration and open deep space access to new actors."
- Following the recent announcement of the GES ground segment upgrade to form the world's first deep space commercial node, the partners are now jointly committed to the developing the Lunar Pathfinder space segment for a low cost "Ride and Phone Home" capability. The Lunar Pathfinder mission will offer a ticket to lunar orbit for payloads and nanosats onboard an SSTL lunar mothership spacecraft, which will provide communications data relay and navigation services between customer payloads and the GES Deep Space ground station.
• October 19, 2018: Satellite communications innovator and space gateway Goonhilly Earth Station has opened an office at the Cody Technology Park in Farnborough, Hampshire, UK, in support of the firm's plans to expand their consultancy, design engineering and small-scale manufacturing capabilities — The new office is located at the Cody Technology Park, Farnborough, Hampshire GU14 0LX. 22)
- The new site gives Goonhilly more space to expand their design engineering team and attract talented engineers in the South-East and South-West of England who are keen to work at the forefront of the UK's flourishing satellite communications sector. The teams in Farnborough and Goonhilly will collaborate closely.
- For example, while the Farnborough team will be focused on deep space antenna array design, their colleagues in Cornwall will undertake the implementation. Goonhilly is also recruiting and investing in small-scale advanced manufacturing/production facilities at their Cornwall headquarters, where it plans to build these next-generation systems.
Ultra-precise navigation — Delta-DOR
When Cebreros (DSA 2), ESA's second deep-space antenna, entered operation in late 2005, the Agency could begin using 'delta-DOR', a powerful new navigation technique particularly important for interplanetary craft. The Cebreros station, DSA 2 (Deep Space Antenna 2), is located 77 km west of Madrid, Spain. It hosts a 35-meter antenna with transmission and reception in X-band and reception in Ka-band. It provides routine support to deep-space missions including Mars Express, Gaia and Rosetta. 23)
ESA's delta-DOR (delta - Differential One-way Range) system has already contributed to Venus Express' successful orbit insertion in April 2006 and to Rosetta's Mars swingby in February 2007, and will become a fundamental tool for navigating all of ESA's current and future interplanetary missions.
Background: Routine navigation of a spacecraft around the Solar System relies on two tracking methods: ranging and two-way Doppler.
Precisely measuring the time it takes radio signals to travel to and from a spacecraft gives the distance from the ground station ('two-way range'), while measuring the signal's Doppler shift (the shift in frequency due to relative movement between the transmitter and receiver) provides the craft's velocity along that line-of-sight ('range-rate').
The other two position coordinates, against the sky background, are obtained only indirectly from the motion of the ground station as the Earth rotates. These position components, though, can only be deduced to much lower accuracy. Usually, tracking over several days is necessary and this requires very high-fidelity modelling of the spacecraft's motion.
Figure 16: Artist's view of Rosetta passing asteroid Lutetia (image credit: ESA - C. Carreau)
The tracking system at ESA's 35m deep-space stations, New Norcia (DSA 1) in Western Australia, Cebreros (DSA 2) near Madrid, and Malargüe (DSA 3), Argentina, provides very accurate measurements. Typically, the random errors on range are about 1 m and on the two-way range-rate less than 0.1 mm/s.
Nevertheless, the limitations described above mean the accuracy of resulting orbit determination may not be good enough for navigation during critical stages of a mission. This is especially the case on approaching a planet before landing, performing a swing-by or insertion into orbit.
Delta-DOR (delta - Differential One-way Range)
However, ESA can now augment conventional tracking by measurements using delta-DOR. NASA's Deep Space Network (DSN) has provided delta-DOR data since 1980 and has aided the navigation of ESA missions since 1986.
Figure 17: Delta-DOR is used to precisely locate spacecraft (image credit: ESA)
The delta-DOR technique for navigating interplanetary spacecraft is based on a simple but effective concept. Delta-DOR uses two widely separated antennas to simultaneously track a transmitting probe in order to measure the time difference (delay time) between signals arriving at the two stations. The technique of measuring this delay is named Differential One-way Range (DOR).
Theoretically, the delay depends only on the positions of the two antennas and the spacecraft. However, in reality, the delay is affected by several sources of error: for example, the radio waves travelling through the troposphere, ionosphere and solar plasma, and clock instabilities at the ground station.
Quasars: brightest beacons. Delta-DOR corrects these errors by tracking a quasar – an active galatic nucleus – that is seen in a direction close to the spacecraft for calibration. The chosen quasar's direction is already known extremely accurately through astronomical measurements, typically to better than 50 billionths of a degree (a nanoradian).
Figure 18: Artist impression of a quasar located in a primeval galaxy, around 900 million years after the Big Bang (image credit: NASA/ESA/ESO/W. Freudling (ST-ECF)
The quasar is usually within 10º of the spacecraft so that the two sources' signal paths through Earth's atmosphere are similar. In principle, the delay time of the quasar is subtracted from that of the spacecraft's to provide the ΔDOR measurement (the Greek symbol 'delta' is commonly used to denote 'difference'). The delay is converted to distance by multiplying by the speed of light.
A complication is that the quasar and spacecraft cannot be measured simultaneously. In practice, three scans are made: spacecraft-quasar-spacecraft or quasar-spacecraft-quasar, and then interpolation between the first and third converts them to the same time as the second measurement, from which the ΔDOR data point is calculated.
ΔDOR has been used with all ESA interplanetary spacecraft including Mars Express, Venus Express and Rosetta, and will be used with future missions such as Gaia.
Figure 19: ESA's ultra-precise deep-space navigation technique – Delta-DOR – tells us where spacecraft are, accurate to within a few hundred meters, even at a distance of 100,000,000 km. In order to navigate a spacecraft around our Solar System we have to know how far away it is, how fast it is travelling and in what direction. Each of these steps are explained in this new infographic, "How not to lose a spacecraft" (image credit: ESA)
ESA and DLR agree on mission control coordination
• April 2, 2019: An existing deep-space dish antenna at the DLR Weilheim site, near Munich, may offer an almost-readymade solution to the problem of providing sufficient ground station capacity to support ESA's current and future deep-space exploration missions. Now and in the next few years, ESA is sending some of the most advanced spacecraft ever flown to exotic locations like Mars, Mercury and Jupiter, and these missions all have one thing in common: they need plenty of ground station capacity to download their masses of science data and to enable mission controllers to send up commands. 24)
ESA already has three state-of-the-art ground tracking stations – identifiable by their big 35 m-diameter dish antennas – located in Australia, Spain and Argentina. These countries are located at longitudes about 120 degrees apart, so that the three stations can provide global coverage for missions voyaging in virtually any direction in our Solar System.
"The stations were built between 2002 and 2012, and their capacity in transmitting and receiving data will soon be reached, given the ambitious missions like BepiColombo, ExoMars and Juice now being implemented – and the fact that these newer spacecraft can all download tremendous amounts of science data," says Pier Bargellini, responsible for the operation of ESA's ground facilities.
With an eye to solving the challenge, engineers at ESA and DLR (German Aerospace Center) have begun assessing the possibility of using an existing 30 m-diameter dish antenna at Weilheim, 60 km south-west of Munich, to provide some add-on tracking capacity at the European longitude. This could solve part of the capacity problem on this continent while at the same time reusing existing European infrastructure and reducing the need for costly new construction.
DLR Weilheim features a number of dish antennas with varying sizes and the site is operated 24 hours/day to support near-Earth missions such as TerraSAR-X, TanDEM-X and GRACE Follow On controlled from DLR's GSOC (German Space Operations Center) at Oberpfaffenhofen. The smaller antennas are also used to support ESA missions orbiting Earth, like Integral.
The 30m dish antenna supported ESA missions in the past, and is presently used when DLR supports partner agencies, such as downloading data from the Hayabusa-2 mission flown by JAXA of Japan. It has also recently been used to receive signals from global navigation satellites like GPS and Galileo.
A series of initial tests conducted by DLR and ESA engineers in the past few months proved that the dish and its sophisticated radio equipment could receive signals from current ESA missions, including Gaia and Mars Express.
"Since the 30m antenna was designed for solar and deep space missions, we are happy to see ESA's interest in bringing it back to its original purpose," says Rolf Kozlowski, head of the DLR Communications and Ground Stations department. "To integrate the antenna into the ESA network would be a challenging but rewarding task for DLR."
"In addition to the reception functionality, the antenna could be upgraded to add transmission capabilities. Its overall characteristics makes it ideal to support missions at lunar distances or even missions to the Lagrange points."
In addition to supporting future ESA and European missions, upgrading the dish would also enable DLR to expand its use for their own future missions or for those of partner agencies. Such cross-support arrangements are common in the field of spacecraft operations, and are typically done on an hour-for-hour exchange basis or in exchange for sharing a mission's scientific data. Engineers from the two agencies will continue testing the Weilheim antenna, with the aim of proving its ability to begin serving as a functional communications backup for ESA missions like Gaia and Mars Express.
Figure 20: Photo of the DLR/GSOC ground station at the Weilheim site with a 30 m deep-space antenna at left. DLR is operating its ground station around the clock on a seven-day week. The ground station is connected with GSOC in Oberpfaffenhofen via a dedicated redundant communications link. GSOC coordinates the operation of all antennas and provides all TTC services and data processing for its satellite missions, including of leasing services to external customers (image credit: DLR/GSOC)
ESA and DLR signed cooperation agreement on 19 December 2018. Joint activities between ESA and national space agencies in the area of communications are excellent examples of how Europe can become even more capable and stronger by developing a ‘network of operational centers'. By linking the efforts of control centers operated by ESA and agencies like DLR, and their ground stations, resources can be shared – and European missions, industry and space ventures can benefit overall, making Europe even more competitive and attractive for international partnership in space. 25)
Hence, ESOC (European Space Operations Center) European in Darmstadt and the GSOC (German Space Operations Center) in Oberpfaffenhofen near Munich have agreed to exploit shared know-how in the fields of mission operations and ground-based infrastructure, jointly developing new concepts, technologies and procedures.
The cooperation agreement was signed on 18 December 2018 at DLR's research center in Oberpfaffenhofen during an Interoperability Plenary meeting, which brought together representatives from 12 space agencies worldwide.
"Public space infrastructure should be used as effectively as possible. ESA therefore endeavors to establish a European network of competence centers. Close cooperation between ESOC and GSOC, as well as subsequent cooperation with other agencies and organizations, should strengthen Europe's position as a partner and competitor in the world market," explains Rolf Densing, ESA's Director of Operations and Head of ESOC.
Figure 21: ESA and DLR signed the cooperation agreement. Rolf Densing (left), Hansjörg Dittus and Felix Huber (right), image credit: DLR
"We look forward to working with ESA to lay the groundwork for a European network of control centers," says Hansjörg Dittus, DLR Executive Board member responsible for space research and technology.
Felix Huber, Director of DLR's Space Operations and Astronaut Training facility adds, "The German Space Operations Center can contribute its expertise in the preparation and execution of crewed and uncrewed missions, further strengthening Germany's position as a space nation in Europe".
The newly announced cooperation between ESOC and GSOC covers five areas: ground control systems, ground stations, space security and on-orbit servicing, post-International Space Station activities and crewed spaceflight, as well as general cooperation.
With respect to the development of ‘ground segments' – the hardware, software and networks on ground used to operate and spacecraft in orbit – both control centers are already working on software for joint mission operations, the so-called European Ground Systems Common Core (EGS-CC).
Further planning includes a project to develop and set up a network of optical ground stations that will enable data transmission by laser. This will enable, for example, quantum keys to be transmitted to support secure communication in the future.
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12) "ESA's new deep space antenna in Cebreros becomes a reality," ESA, September 2005, URL: http://m.esa.int/About_Us/ESOC/ESA_s_new_deep_space_antenna
13) "Malargüe - DSA 3," ESA, URL: https://www.esa.int/Our_Activities/Operations/Estrack/Malarguee_-_DSA_3
14) "ESA boosting its Argentine link with deep space," ESA, 25 April 2017, URL: http://m.esa.int/Our_Activities/Operations/Estrack/ESA_boosting
15) "Doing up the deep dish," ESA, 11 April 2019, URL: http://m.esa.int/spaceinimages/Images/2019/Doing_up_the_deep_dish
16) "Goonhilly goes deep space," ESA, 22 February, 2018, URL: https://m.esa.int/Our_Activities/Operations/Estrack/Goonhilly_goes_deep_space
17) "Goonhilly Partners with the Australian Space Agency to Drive New Opportunities Worldwide," Space Daily, 27 February 2019, URL: http://www.spacedaily.com/reports/Goonhilly_Partners_with_the_Australian
18) "Goonhilly Brings Data Center and Cloud Expert Onboard," Satnews Daily, 29 January, 2019, URL: http://www.satnews.com/story.php?number=2085857603
19) "The Satellite Applications Catapult Partners with Infostellar to Provide Improved Ground Station Access," Satnews Daily, 7 January 2019, URL: http://www.satnews.com/story.php?number=1589105641
20) "Goonhilly partners with Airbus, other industry leaders and academics in proposed SmartSat CRC to drive Australia's space sector," Space Daily, 23 November 2018, URL: http://www.spacedaily.com/reports/Goonhilly_partners_with_Airbus_other_industry
21) "ESA signs collaboration agreement for commercial lunar missions," ESA, 17 April 2018, URL: https://www.esa.int/Our_Activities/Human_Spaceflight/ESA
22) "Goonhilly Earth Station Expands Their Operations Enabling Multitasking in Multi Locations," Satnews Daily, 19 October 2018, URL: http://www.satnews.com/story.php?number=1798184766
23) "About delta DOR," ESA, Operations image of the week, 07 February 2019, URL: http://m.esa.int/Our_Activities/Operations/About_delta_DOR
24) "ESA and DLR in joint study to support deep space missions," ESA, 2 April 2019, URL: http://m.esa.int/Our_Activities/Operations/ESA_and_DLR
25) Space in Europe: ESA and DLR agree on mission control operation," ESA, 19 December 2018, URL: https://www.esa.int/About_Us/ESOC/Space_in_Europe_ESA_and_DLR_agree
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).