A ground segment consists of all the ground-based elements of a spacecraft system used by operators and support personnel, as opposed to the space segment and user segment.:1 The ground segment enables management of a spacecraft, and distribution of payload data and telemetry among interested parties on the ground. The primary elements of a ground segment are:
These elements are present in nearly all space missions, whether commercial, military, or scientific. They may be located together or separated geographically, and they may be operated by different parties.:25 Some elements may support multiple spacecraft simultaneously.
Ground stations provide radio interfaces between the space and ground segments for telemetry, tracking, and command (TT&C), as well as payload data transmission and reception.:4 Tracking networks, such as NASA's Near Earth Network and Space Network, handle communications with multiple spacecraft through time-sharing.:22
Ground station equipment may be monitored and controlled remotely, often via serial and/or IP interfaces. There are typically backup stations from which radio contact can be maintained if there is a problem at the primary ground station which renders it unable to operate, such as a natural disaster. Such contingencies are considered in a Continuity of Operations plan.
Signals to be uplinked to a spacecraft must first be extracted from ground network packets, encoded to baseband, and modulated, typically onto an intermediate frequency (IF) carrier, before being up-converted to the assigned radio frequency (RF) band. The RF signal is then amplified to high power and carried via waveguide to an antenna for transmission. In colder climates, electric heaters or hot air blowers may be necessary to prevent ice or snow buildup on the parabolic dish.
Received ("downlinked") signals are passed through a low-noise amplifier (often located in the antenna hub to minimize the distance the signal must travel) before being down-converted to IF; these two functions may be combined in a low-noise block downconverter. The IF signal is then demodulated, and the data stream extracted via bit and frame synchronization and decoding. Data errors, such as those caused by signal degradation, are identified and corrected where possible. The decoded data stream is then packetized or saved to files for transmission on the ground network. Ground stations may temporarily store received telemetry for later playback to control centers, often when ground network bandwidth is not sufficient to allow real-time transmission of all received telemetry.
A single spacecraft may make use of multiple RF bands for different telemetry, command, and payload data streams, depending on bandwidth and other requirements.
The timing of passes, when a line of sight exists to the spacecraft, is determined by the location of ground stations, and by the characteristics of the spacecraft orbit or trajectory. The Space Network uses geostationary relay satellites to extend pass opportunities over the horizon.
Ground stations must track spacecraft in order to point their antennas properly, and must account for Doppler shifting of RF frequencies due to the motion of the spacecraft. Ground stations may also perform automated ranging; ranging tones may be multiplexed with command and telemetry signals. Ground station tracking and ranging data are passed to the control center along with spacecraft telemetry.
Mission control centers process, analyze, and distribute spacecraft telemetry, and issue commands, data uploads, and software updates to spacecraft. For manned spacecraft, mission control manages voice and video communications with the crew. Control centers may also be responsible for configuration management and data archival. As with ground stations, there are typically backup control facilities available to support continuity of operations.
Control centers use telemetry to determine the status of a spacecraft and its systems.:485 Housekeeping, diagnostic, science, and other types of telemetry may be carried on separate virtual channels. Flight control software performs the initial processing of received telemetry, including:
A spacecraft database is called on to provide information on telemetry frame formatting, the positions and frequencies of parameters within frames, and their associated mnemonics, calibrations, and soft and hard limits. The contents of this database—especially calibrations and limits—may be updated periodically to maintain consistency with onboard software and operating procedures; these can change during the life of a mission in response to upgrades, hardware degradation in the space environment, and changes to mission parameters.
Commands sent to spacecraft are formatted according to the spacecraft database, and are validated against the database before being transmitted via a ground station. Commands may be issued manually in real time, or they may be part of automated or semi-automated procedures. Typically, commands successfully received by the spacecraft are acknowledged in telemetry, and a command counter is maintained on the spacecraft and at the ground to ensure synchronization. In certain cases, closed-loop control may be performed. Commanded activities may pertain directly to mission objectives, or they may be part of housekeeping. Commands (and telemetry) may be encrypted to prevent unauthorized access to the spacecraft or its data.
Spacecraft procedures are often developed and tested against a spacecraft simulator prior to use with the actual spacecraft.
Dedicated physical spaces may be provided in the control center for certain mission support roles, such as flight dynamics and network control,:475 or these roles may be handled via remote terminals outside the control center. As on-board computing power and flight software complexity have increased, there is a trend toward performing more automated data processing on board the spacecraft.:2–3
Control centers may be continuously or regularly staffed by flight controllers. Staffing is typically greatest during the early phases of a mission,:21 and during critical procedures and periods. Increasingly commonly, control centers for unmanned spacecraft may be set up for "lights-out" (or automated) operation, as a means of controlling costs. Flight control software will typically generate notifications of significant events – both planned and unplanned – in the ground or space segment that may require operator intervention.
Ground networks handle data transfer and voice communication between different elements of the ground segment. These networks often combine LAN and WAN elements, for which different parties may be responsible. Geographically separated elements may be connected via leased lines or virtual private networks. The design of ground networks is driven by requirements on reliability, bandwidth, and security.
Reliability is a particularly important consideration for critical systems, with uptime and mean time to recovery being of paramount concern. As with other aspects of the spacecraft system, redundancy of network components is the primary means of achieving the required system reliability.
Security considerations are vital to protect space resources and sensitive data. WAN links often incorporate encryption protocols and firewalls to provide information and network security. Antivirus software and intrusion detection systems provide additional security at network endpoints.
Remote terminals are interfaces on ground networks, separate from the mission control center, which may be accessed by payload controllers, telemetry analysts, instrument and science teams, and support personnel, such as system administrators and software development teams. They may be receive-only, or they may transmit data to the ground network.
Terminals used by service customers, including ISPs and end users, are collectively called the "user segment", and are typically distinguished from the ground segment. User terminals including satellite television systems and satellite phones communicate directly with spacecraft, while other types of user terminals rely on the ground segment for data receipt, transmission, and processing.
Space vehicles and their interfaces are assembled and tested at integration and test (I&T) facilities. I&T provides an opportunity to fully test communications with, and behavior of, the spacecraft prior to launch.
Vehicles are delivered to space via launch facilities, which handle the logistics of rocket launches. Launch facilities are typically connected to the ground network to relay telemetry prior to and during launch. The launch vehicle itself is sometimes said to constitute a "transfer segment", which may be considered distinct from both the space and ground segments.:21
Costs associated with the establishment and operation of a ground segment are highly variable, and depend on accounting methods. According to a study by Delft University of Technology,[Note 1] the ground segment contributes approximately 5% to the total cost of a space system. According to a report by the RAND Corporation on NASA small spacecraft missions, operation costs alone contribute 8% to the lifetime cost of a typical mission, with integration and testing making up a further 3.2%, ground facilities 2.6%, and ground systems engineering 1.1%.:10
Ground segment cost drivers include requirements placed on facilities, hardware, software, network connectivity, security, and staffing. Ground station costs in particular depend largely on the required transmission power, RF band(s), and the suitability of preexisting facilities.:703 Control centers may be highly automated as a means of controlling staffing costs.
1worldspace, known for most of its existence simply as 'WorldSpace', is a defunct satellite radio network that in its heyday provided service to over 170,000 subscribers in eastern and southern Africa, the Middle East, and much of Asia with 96% coming from India. It was profitable in India, with 450,000 subscribers.Timbre Media along with Saregama India planned to relaunch the company.The satellites AfriStar and AsiaStar however are now being used by the Yazmi USA, LLC run by WorldSpace's former CEO Noah A. Samara. The company claims to have built the first satellite-to-tablet content delivery system. The system primarily aims at providing educational services to rural areas in developing countries. The first pilots of the technology are said to be taking place in India (with 30,000 licenses) and the sub-Saharan region in Africa, with the latest trials in two schools in South Africa, in Rietkol, in Mpumalanga Province, and at Heathfield, in Western Cape.Athena-Fidus
Athena-Fidus (Access on theatres for European allied forces nations-French Italian dual use satellite) is a French-Italian telecommunication satellite providing high-throughput secure communications to both nation's armed forces and their emergency services. It was manufactured by Thales Alenia Space under the supervision of CNES, the DGA and the Italian Space Agency. It complements the lower-throughput but more secure Syracuse 3 satellites. The satellite has a wet mass of 3 tonnes and was placed on Geostationary orbit in 2014. Its expected lifetime is 15 years.COSMO-SkyMed
COSMO-SkyMed (COnstellation of small Satellites for the Mediterranean basin Observation) is an Earth observation satellite space-based radar system funded by the Italian Ministry of Research and Ministry of Defence and
conducted by the Italian Space Agency (ASI), intended for both military and civilian use.The space segment of the system includes four identical medium-sized satellites equipped with synthetic aperture radar (SAR) sensors with global coverage of the planet. Observations of an area of interest can be repeated several times a day in all-weather conditions.
The imagery will be applied to defense and security assurance in Italy and other countries, seismic hazard analysis, environmental disaster monitoring, and agricultural mapping.DORIS (geodesy)
Doppler Orbitography and Radiopositioning Integrated by Satellite or, in French, Détermination d'Orbite et Radiopositionnement Intégré par Satellite (in both case yielding the acronym DORIS) is a French satellite system used for the determination of satellite orbits (e.g. TOPEX/Poseidon) and for positioning.Deimos-2
Deimos-2 is a Spanish remote sensing Earth observation satellite built for Elecnor Deimos under an agreement with Satrec Initiative, a satellite manufacturing company in South Korea.
The Earth observation system was developed by Elecnor Deimos, who managed the engineering, ground segment, integration, tests, launch contract and LEOP, in collaboration with Satrec Initiative, who provided the platform and the payload. The platform is based on DubaiSat-2 launched in 2013, with a larger battery pack intended to last for at least 7 years. The satellite was purchased by Urthecast in 2015, together with Deimos-1 and Deimos Imaging, the division of Elecnor Deimos that was in charge of the operation of both satellites.
Deimos-2 is currently property of Deimos Imaging, who operates it and commercialises its data.DubaiSat-2
DubaiSat-2 is an electro-optical Earth observation satellite built by the Emirates Institution for Advanced Science and Technology under an agreement with Satrec Initiative, a satellite manufacturing company in South Korea. EIAST’s objective with DubaiSat-2 is to provide electro-optical images, that can be commercialized, for users within the United Arab Emirates and beyond and to develop and implement new technologies not used in DubaiSat-1. EIAST also intends to continue manpower training for the UAE’s space program. 16 UAE engineers have been working on the design, development, testing and manufacturing of the satellite. The participation of the UAE engineers, who are currently working in South Korea, has increased by 100 per cent from the DubaiSat-1 project.European Data Relay System
The European Data Relay System (EDRS) system is a European constellation of state of the art GEO satellites that relay information and data between satellites, spacecraft, UAVs, and ground stations. The designers intend the system to provide almost full-time communication, even with satellites in low Earth orbit that often have reduced visibility from ground stations. It makes on-demand data available to, for example, rescue workers who want near-real-time satellite data of a crisis region.
The system has been developed as part of the ARTES 7 programme and is intended to be an independent, European satellite system that reduces time delays in the transmission of large quantities of data. The programme is similar to the American Tracking and Data Relay Satellite System that was set up to support the Space Shuttle—but EDRS is using a new generation Laser Communication Terminal (LCT) technology. The laser terminal transmits 1.8 Gbit/s across 45,000 km, the distance of a LEO-GEO link. Such a terminal was successfully tested during in-orbit verification between the German radar satellite TerraSAR-X and the American NFIRE satellite. It is also embarked on the commercial telecommunication satellite Alphasat.Ground station
For stations controlling unmanned aerial vehicles (UAVs), see Ground control station.A ground station, earth station, or earth terminal is a terrestrial radio station designed for extraplanetary telecommunication with spacecraft (constituting part of the ground segment of the spacecraft system), or reception of radio waves from astronomical radio sources. Ground stations may be located either on the surface of the Earth, or in its atmosphere. Earth stations communicate with spacecraft by transmitting and receiving radio waves in the super high frequency or extremely high frequency bands (e.g., microwaves). When a ground station successfully transmits radio waves to a spacecraft (or vice versa), it establishes a telecommunications link. A principal telecommunications device of the ground station is the parabolic antenna.
Ground stations may have either a fixed or itinerant position. Article 1 § III of the ITU Radio Regulations describes various types of stationary and mobile ground stations, and their interrelationships.Specialized satellite earth stations are used to telecommunicate with satellites—chiefly communications satellites. Other ground stations communicate with manned space stations or unmanned space probes. A ground station that primarily receives telemetry data, or that follows a satellite not in geostationary orbit, is called a tracking station.
When a satellite is within a ground station's line of sight, the station is said to have a view of the satellite (see pass). It is possible for a satellite to communicate with more than one ground station at a time. A pair of ground stations are said to have a satellite in mutual view when the stations share simultaneous, unobstructed, line-of-sight contact with the satellite.ITUpSAT1
ITUpSAT1, short for Istanbul Technical University picoSatellite-1) is a single CubeSat built by the Faculty of Aeronautics and Astronautics at the Istanbul Technical University. It was launched on September 23, 2009 atop a PSLV-C14 satellite launch vehicle from Satish Dhawan Space Centre, Sriharikota, Andhra Pradesh in India, and became the first Turkish university satellite to orbit the Earth. It was expected to have a minimum of six-month life term, but it is still functioning for over two years. It is a picosatellite with side lengths of 10 cm (3.9 in) and a mass of 0.990 kg (2.18 lb).
The overall objectives are to provide a hands-on project environment for the students at the ITU under faculty guidance. The mission goals are to capture imagery of the CMOS payload, and to study the behavior of the passive stabilization system of the CubeSat.Indian Regional Navigation Satellite System
The Indian Regional Navigation Satellite System (IRNSS), with an operational name of NAVIC ("sailor" or "navigator" in Sanskrit, Hindi and many other Indian languages and also standing for NAVigation with Indian Constellation), is an autonomous regional satellite navigation system that provides accurate real-time positioning and timing services. It covers India and a region extending 1,500 km (930 mi) around it, with plans for further extension. An Extended Service Area lies between the primary service area and a rectangle area enclosed by the 30th parallel south to the 50th parallel north and the 30th meridian east to the 130th meridian east, 1,500–6,000 km beyond borders. The system at present consists of a constellation of seven satellites, with two additional satellites on ground as stand-by.The constellation is in orbit as of 2018, and the system was expected to be operational from early 2018 after a system check. NAVIC will provide two levels of service, the "standard positioning service", which will be open for civilian use, and a "restricted service" (an encrypted one) for authorized users (including military). Due to the failures of one of the satellites and its replacement, no new date for operational status has been set.
There are plans to expand NavIC system by increasing constellation size from 7 to 11.International Cospas-Sarsat Programme
The International Cospas-Sarsat Programme is a satellite-aided search and rescue initiative. It is organized as a treaty-based, nonprofit, intergovernmental, humanitarian cooperative of 44 nations and agencies (see infobox). It is dedicated to detecting and locating radio beacons activated by persons, aircraft or vessels in distress, and forwarding this alert information to authorities that can take action for rescue.The system utilizes a network of satellites that provide coverage anywhere on Earth. Distress alerts are detected, located and forwarded to over 200 countries and territories at no cost to beacon owners or the receiving government agencies. Cospas-Sarsat was conceived and initiated by Canada, France, the United States, and the former Soviet Union in 1979. The first rescue using the technology of Cospas-Sarsat occurred in September 1982. The definitive agreement of the organization was signed on 1 July 1988.Mission control center
A mission control center (MCC, sometimes called a flight control center or operations center) is a facility that manages space flights, usually from the point of launch until landing or the end of the mission. It is part of the ground segment of spacecraft operations. A staff of flight controllers and other support personnel monitor all aspects of the mission using telemetry, and send commands to the vehicle using ground stations. Personnel supporting the mission from an MCC can include representatives of the attitude control system, power, propulsion, thermal, attitude dynamics, orbital operations and other subsystem disciplines. The training for these missions usually falls under the responsibility of the flight controllers, typically including extensive rehearsals in the MCC.Multi-Functional Transport Satellite
Multifunctional Transport Satellites (MTSAT) were a series of weather and aviation control satellites. They are replaced by Himawari 8 on 7 July 2015. They were geostationary satellites owned and operated by the Japanese Ministry of Land, Infrastructure, Transport and Tourism and the Japan Meteorological Agency (JMA), and provide coverage for the hemisphere centred on 140° East; this includes Japan and Australia who are the principal users of the satellite imagery that MTSAT provides. They replace the GMS-5 satellite, also known as Himawari 5 (“himawari” or “ひまわり” meaning “sunflower”). They can provide imagery in five wavelength bands — visible and four infrared, including the water vapour channel. The visible light camera has a resolution of 1 km; the infrared cameras have 4 km (resolution is lower away from the equator at 140° East). The spacecraft have a planned lifespan of five years. MTSAT-1 and 1R were built by Space Systems/Loral. MTSAT-2 was built by Mitsubishi.Radarsat-2
RADARSAT-2 is an Earth observation satellite that was successfully launched December 14, 2007 for the Canadian Space Agency by Starsem, using a Soyuz FG launch vehicle, from Kazakhstan's Baikonur Cosmodrome. RADARSAT-2 was previously assembled, integrated and tested at the David Florida Laboratory near Ottawa, Ontario before the start of its launch campaign.
The end of the spacecraft and ground segment commissioning period was declared on April 27, 2008 after which routine commercial operation started.
The satellite has a C-band Synthetic Aperture Radar (SAR) with multiple polarization modes, including a fully polarimetric mode in which HH, HV, VV and VH polarized data are acquired. Its highest resolution is 1 m in Spotlight mode (3 m in Ultra Fine mode). In ScanSAR Wide Beam mode the SAR has a nominal swath width of 500 km and an imaging resolution of 100 m. Its left looking capability allows the spacecraft the unique capability to image the Antarctic on a routine basis providing data in support of scientific research.
The prime contractor on the project is MacDonald Dettwiler and Associates (MDA), who have previously built projects such as the Canadarm. Other collaborating companies included EMS Technologies and Alenia. EMS Space & Technology/Montreal division was bought by MDA in 2005. RADARSAT-2 is owned and operated by MDA.
RADARSAT-2 is a follow-on to RADARSAT-1 which mission terminated in April 2013. It has the same orbit (798 km altitude sun-synchronous orbit with 6 p.m. ascending node and 6 a.m. descending node). Some of the orbit characteristics are 24 days repeat cycle (=343 orbits), 14.29 orbits per day, each orbit being 100.75 minutes duration. It is filling a wide variety of application, including sea ice mapping and ship routing, iceberg detection, agricultural crop monitoring, marine surveillance for ship and pollution detection, terrestrial defence surveillance and target identification, geological mapping, mine monitoring, land use mapping, wetlands mapping, topographic mapping.
On 4 July 2009, Canada's Department of National Defence announced their intention to increase RADARSAT-2 usage for surveillance of Canada's coastlines and the Arctic. To carry out this new project, the satellite's owner MacDonald Dettwiler and Associates (MDA) of Richmond, B.C., was awarded $25-million contract to carry out upgrades (called project Polar Epsilon) to enhance the satellites capabilities to detect surface ships. The upgrades consisted of creating new beam mode (OSVN and DVWF) that target improvements in maritime vessels detection over a broad area, as well as upgrading the RADARSAT-2 ground segment to improve conflict resolution with other government users. Two new ground stations for the data reception have been built, one on the east coast at Masstown, N.S., and the other at Aldergrove, B.C. (west coast). These two new stations are mainly used for the Polar Epsilon project.By mid-August 2015, the addition of the Canada Centre for Mapping and Earth Observation (CCMEO) X Band receiving station in Inuvik has significantly increased RADARSAT-2 downlink capacity in Canada. The network of ground receiving station continues to expand with 19 partners organization using 46 antennas at various reception sites.
As of January 2018, RADARSAT-2 is entering its 10th operational service year. Numerous enhancements have been added to the original capabilities both on the ground and on the space segments. The operational performance is well within the specification with an acquisition success rate above 97% (Acquisition successfully executed Vs Acquisition loaded on the Spacecraft for execution) and a percentage of availability of 99.95% (hours of outage Vs total hours in a year). The usage of SAR data have been steadily growing from an average of 3.5 minutes per orbit in 2008 to an average of 11.38 minutes per orbit in 2018.Soil Moisture and Ocean Salinity
Soil Moisture and Ocean Salinity, or SMOS, is a satellite which forms part of ESA's Living Planet Programme. It is intended to provide new insights into Earth's water cycle and climate. In addition, it is intended to provide improved weather forecasting and monitoring of snow and ice accumulation.Space Variable Objects Monitor
The Space Variable Objects Monitor (SVOM) is a planned small X-ray telescope satellite under development by China National Space Administration (CNSA) and the French Space Agency (CNES), to be launched in 2021.SVOM will study the explosions of massive stars by analysing the resulting gamma-ray bursts. The light-weight X-ray mirror for SVOM weighs just 1 kg (2.2 lb). SVOM will add new capabilities to the work of finding gamma-ray bursts currently being done by the multinational satellite Swift.Its anti-solar pointing strategy makes the Earth cross the field of view of its payload every orbit.Spirale
Spirale is a French government programme to develop an early warning system which will use infrared satellite imagery to detect the flights of ballistic missiles during their boost phase, just after launch. SPIRALE is an acronym which stands for "Système Préparatoire Infra-Rouge pour l’ALErte", literally "infrared preparatory system for alert".
The demonstrator system includes two 120 kilograms (260 lb) microsatellites and an alert and monitoring ground segment. The satellites have been launched by Ariane 5 on 12 February 2009.Telespazio VEGA UK
Telespazio VEGA UK Ltd. is a British space company based in Luton, Bedfordshire. Founded in 1978 by a small group of engineers at the European Space Operations Centre (ESOC) in Darmstadt, Germany, VEGA now works with Space agencies, satellite operators and manufacturers around the world. It works with the European Space Agency (ESA) and ESOC in Germany, European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands, ESA Centre for Earth Observation (ESRIN) in Rome, Italy, and European Space Astronomy Centre (ESAC) in Madrid, Spain.
Since 1978, VEGA has worked on almost every ESA mission and many other European and international programmes, including Mars Express, the Automated Transfer Vehicle (ATV) for the International Space Station (ISS), the Eumetsat Polar System, and the Ground Segment Development for ADEN.
On 1 January 2011, VEGA Space Ltd, became a part of Telespazio, the Rome-based space systems services company. It was previously a part of Finmeccanica (now Leonardo, having been originally acquired in 2008 as VEGA Group PLC.
Telespazio VEGA is an active member of UKspace, the trade association for Britain’s space industry, and is heavily involved with the International Space Innovation Centre based in Harwell.TerraSAR-X
TerraSAR-X, an imaging radar Earth observation satellite, is a joint venture being carried out under a public-private-partnership between the German Aerospace Center (DLR) and EADS Astrium. The exclusive commercial exploitation rights are held by the geo-information service provider Astrium. TerraSAR-X was launched on 15 June 2007 and has been in operational service since January 2008. With its twin satellite TanDEM-X, launched 21 June 2010, TerraSAR-X acquires the data basis for the WorldDEM, the worldwide and homogeneous DEM available from 2014.