Ground segment
A ground segment consists of all the ground-based elements of a
- Ground (or Earth) stations, which provide radio interfaces with spacecraft[2]: 142
- Mission control (or operations) centers, from which spacecraft are managed[3]: 20
- Remote terminals, used by support personnel[2]: 142
- Spacecraft integration and test facilities
- Launch facilities[3]: 21
- Ground networks, which allow for communication between the other ground elements[2]: 142 [4]
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.[5][6]: 25 Some elements may support multiple spacecraft simultaneously.[7]: 480, 481
Elements
Ground stations
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.[6]: 4 [8][9] Tracking networks, such as NASA's Near Earth Network and Space Network, handle communications with multiple spacecraft through time-sharing.[3]: 22
Ground station equipment may be monitored and controlled remotely. There are often 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.
Transmission and reception
Signals to be
Received ("downlinked") signals are passed through a
A single spacecraft may make use of multiple RF bands for different telemetry, command, and payload data streams, depending on bandwidth and other requirements.
Passes
The timing of
Tracking and ranging
Ground stations must
Mission control centers
Mission control centers process, analyze, and distribute spacecraft telemetry, and issue commands, data uploads, and software updates to spacecraft. For crewed spacecraft, mission control manages voice and video communications with the crew. Control centers may also be responsible for configuration management and data archival.[7]: 483 As with ground stations, there are often backup control facilities available to support continuity of operations.
Telemetry processing
Control centers use telemetry to determine the status of a spacecraft and its systems.[3]: 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:
- Separation and distribution of virtual channels[3]: 393
- Time-ordering and gap-checking of received frames (gaps may be filled by commanding a retransmission)
- Decommutation of parameter values,[10] and association of these values with parameter names called mnemonics
- Conversion of raw data to calibrated (engineering) values, and calculation of derived parameters[7]: 483
- Limit and constraint checking (which may generate alert notifications)[3]: 479 [7]: 484
- Generation of telemetry displays, which may be take the form of tables, plots of parameters against each other or over time, or synoptic displays (sometimes called mimics) – essentially flow diagrams that present component or subsystem interfaces and their state[7]: 484
A spacecraft database provided by the spacecraft manufacturer 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.[7]: 486 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.[12]: 399
Commanding
Commands sent to spacecraft are formatted according to the spacecraft database, and are
Spacecraft procedures are generally developed and tested against a spacecraft
Analysis and support
Mission control centers may rely on "offline" (i.e., non-real-time) data processing subsystems to handle analytical tasks[3]: 21 [7]: 487 such as:
- Orbit determination and maneuver planning[14]
- Conjunction assessment and collision avoidance planning[7]: 478–479
- Mission planning and scheduling[7]: 489–491
- On-board memory management[15]: 247–249
- Short- and long-term trend analysis[3]: 21
- Path planning, in the case of planetary rovers
Dedicated physical spaces may be provided in the control center for certain mission support roles, such as
Staffing
Control centers may be
Remote terminals
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
Integration and test facilities
Space vehicles and their interfaces are assembled and tested at integration and test (I&T) facilities. Mission-specific I&T provides an opportunity to fully test communications between, and behavior of, both the spacecraft and the ground segment prior to launch.[7]: 480
Launch facilities
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 ground and space segments.[3]: 21
Ground networks
Ground networks handle data transfer and voice communication between different elements of the ground segment.[7]: 481–482 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.[7]: 481 The design of ground networks is driven by requirements on reliability, bandwidth, and security. Delay-tolerant networking protocols may be used.
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.
Costs
Costs associated with the establishment and operation of a ground segment are highly variable,[17] 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.[18] 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%.[19]: 10
Ground segment cost drivers include requirements placed on facilities, hardware, software, network connectivity, security, and staffing.[20] Ground station costs in particular depend largely on the required transmission power, RF band(s), and the suitability of preexisting facilities.[17]: 703 Control centers may be highly automated as a means of controlling staffing costs.[16]
- ^ Based on a model described in Space Mission Analysis and Design, third edition, by James W. Wertz and Wiley J. Larson
Images
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Antenna belonging to theDeep Space Network
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Space Telescope Operations Control Center at Goddard Space Flight Center, during servicing of the Hubble Space Telescope
-
Integration of flight hardware at aTsukuba, Japan
-
Decommissioned launch site at the Guiana Space Centre
See also
- Consultative Committee for Space Data Systems(CCSDS), which maintains standards for telemetry and command formatting
- Radiocommunication service, as defined by ITU Radio Regulations
- On-board data handling subsystem
References
- SKY Perfect JSAT Group International. Archived from the originalon 20 September 2015. Retrieved 5 November 2015.
- ^ ISBN 978-1-60807-673-4.
- ^ ISBN 978-0470742419. Retrieved 30 December 2015.
- ^ "ERS Ground Segment". European Space Agency. Retrieved 5 November 2015.
- ^ "Ground Segment Overview". European Space Agency. Retrieved 5 November 2015.
- ^ a b Reiniger, Klaus; Diedrich, Erhard; Mikusch, Eberhard (August 2006). "Aspects of Ground Segment Design for Earth observation missions" (PDF). Alpbach Summer School.
- ^ ISBN 9780470750124.
- SKY Perfect JSAT GroupInternational. Retrieved 5 November 2015.
- SKY Perfect JSAT GroupInternational. Retrieved 5 November 2015.
- ^ a b c d "Chapter 10: Telecommunications". Basics of Spaceflight. NASA Jet Propulsion Laboratory. Retrieved 28 December 2015.
- ^ Wood, Lloyd (July 2006). Introduction to satellite constellations: Orbital types, uses and related facts (PDF). ISU Summer Session. Retrieved 17 November 2015.
- ISBN 9780470750124.
- ISBN 9780470750124.
- ^ "Chapter 13: Spacecraft Navigation". Basics of Spaceflight. NASA Jet Propulsion Laboratory. Retrieved 28 December 2015.
- ISBN 978-3-7091-1802-3. Retrieved 28 December 2015.
- ^ a b c d e "Operations Staffing". Satellite Operations Best Practice Documents. Space Operations and Support Technical Committee, American Institute of Aeronautics and Astronautics. Retrieved 28 December 2015.
- ^ ISBN 1461530067. Retrieved 8 January 2016.
- ^ Zandbergen, B.T.C., "ROM system cost", Cost Estimation for Space System Elements, v.1.02, archived from the original (Excel spreadsheet) on 26 January 2016, retrieved 8 January 2016
- ^ de Weck, Olivier; de Neufville, Richard; Chang, Darren; Chaize, Mathieu. "Technical Success and Economic Failure". Communications Satellite Constellations (PDF). Massachusetts Institute of Technology. Archived from the original (PDF) on 2005-05-09. Retrieved 2016-01-12.
- .